Finding of Significant Contribution and Rulemaking for Certain States in the Ozone Transport Assessment Group Region for Purposes of Reducing Regional Transport of Ozone

SUMMARY: In accordance with the Clean Air Act (CAA), today's action is

a proposed rulemaking to require certain States to submit State

implementation plan (SIP) measures to ensure that emission reductions

are achieved as needed to mitigate transport of ozone (smog) pollution

and one of its main precursors--emissions of oxides of nitrogen

(NOX)-- across State boundaries in the eastern half of the

United States. The States affected by today's action are in the Ozone

Transport Assessment Group (OTAG) Region.

Today's action proposes to find that the transport of ozone from

certain States in the OTAG region (the 37 eastern most States and the

District of Columbia) significantly contributes to nonattainment of the

ozone national ambient air quality standards (NAAQS), or interferes

with maintenance of the NAAQS, in downwind States. This proposal

explains the basis for determining significant contribution or

interference with maintenance for the affected States. Further, by

today's action, EPA is proposing the appropriate levels of

NOX emissions that each of the affected States will be

required to achieve.

The EPA is committed to promulgate final action on the proposed

rule within 12 months from the date of publication of today's action.

DATES: The EPA is establishing a 120-day comment period, ending on

March 9, 1998. For additional information on the comment period, please

refer to SUPPLEMENTARY INFORMATION. A public hearing will be held

during the comment period, if requested. If a public hearing is

requested, EPA will make an announcement in the Federal Register.

ADDRESSES: Documents relevant to this matter are available for

inspection at the Air and Radiation Docket and Information Center

(6101), Attention: Docket No. A-96-56, U.S. Environmental Protection

Agency, 401 M Street SW, room M-1500, Washington, DC 20460, telephone

(202) 260-7548, between 8:00 a.m. and 4:00 p.m., Monday through Friday,

excluding legal holidays. A reasonable fee may be charged for copying.

Comments and data may also be submitted electronically by following the

instructions under SUPPLEMENTARY INFORMATION of this document. No

Confidential Business Information (CBI) should be submitted through e-

mail.

FOR FURTHER INFORMATION CONTACT: General questions concerning today's

action should be addressed to Kimber Smith Scavo, Office of Air Quality

Planning and Standards, Air Quality Strategies and Standards Division,

MD-15, Research Triangle Park, NC 27711, telephone (919) 541-3354.

Please refer to SUPPLEMENTARY INFORMATION below for a list of contacts

for specific subjects described in today's action.

SUPPLEMENTARY INFORMATION:

Comment Period

Because commenters may wish to submit technical information that

may require additional time to develop, EPA will accept additional

pertinent information beyond the 120-day time frame and will do what is

possible to take the information into account for the final rulemaking.

The EPA will make every effort to consider this information. However,

due to the time frames associated with this action, EPA cannot

guarantee that information submitted after the close of the comment

period will be considered. The EPA is committed to publish the final

rulemaking within 12 months of the date of today's action.

Electronic Availability

The official record for this rulemaking, as well as the public

version, has been established under docket number A-96-56 (including

comments and data submitted electronically as described below). A

public version of this record, including printed, paper versions of

electronic comments, which does not include any information claimed as

CBI, is available for inspection from 8 a.m. to 4 p.m., Monday through

Friday, excluding legal holidays. The official rulemaking record is

located at the address in ADDRESSES at the beginning of this document.

Electronic comments can be sent directly to EPA at: A-and-R-

D[email protected]. Electronic comments must be submitted as an

ASCII file avoiding the use of special characters and any form of

encryption. Comments and data will also be accepted on disks in

WordPerfect in 5.1 file format or ASCII file format. All comments and

data in electronic form must be identified by the docket number A-96-

56. Electronic comments on this proposed rule may be filed online at

many Federal Depository Libraries.

Availability of Related Information

Documents related to OTAG are available on the Agency's Office of

Air Quality Planning and Standards' (OAQPS) Technology Transfer Network

(TTN) Bulletin Board System (BBS). The telephone number for the TTN BBS

is (919) 541-5742. To access the bulletin board a modem and

communications software are necessary. The following parameters on the

communications software are required: Data Bits-8; Parity-N; and Stop

Bits-1. The documents are located on the OTAG BBS. The TTN can also be

accessed via the web at http://www.epa.gov/ttn. If assistance is needed

in accessing the system, call the help desk at (919) 541-5384 in

Research Triangle Park, NC. Other documents related to OTAG can be

downloaded from OTAG's webpage at http://www.epa.gov/ttn/otag. The

OTAG's technical data are located at http://www.iceis.mcnc.org/OTAGDC.

For Additional Information

For technical questions related to the determination of significant

contribution, please contact Norm Possiel, Office of Air Quality

Planning and Standards, Emissions, Monitoring, and Analysis Division,

MD-13, Research Triangle Park, NC 27711, telephone (919) 541-5692. For

legal questions, please contact Howard Hoffman, Office of General

Counsel, 401 M Street SW, MC-2344, Washington, DC, 20460, telephone

(202) 260-5892. For questions concerning the statewide emission

budgets, please contact Doug Grano, Office of Air Quality Planning and

Standards, Air Quality Strategies and Standards Division, MD-15,

Research Triangle Park, NC 27711, telephone (919) 541-3292. For

questions concerning SIP approvability, please contact Carla Oldham,

Office of Air Quality Planning and Standards, Air Quality Strategies

and Standards Division, MD-15, Research Triangle Park, NC 27711,

telephone (919) 541-3347. For questions concerning the cost analysis,

please contact Sam Napolitano, Office of Atmospheric Programs, MC-

6201J, 401 M Street SW, Washington, DC 20460, telephone (202) 233-9751.

Outline

I. Preamble

[[Page 60319]]

A. Summary of Rulemaking and Affected States

B. General Factual Background

C. Statutory and Regulatory Background

1. Clean Air Act Provisions

a. 1970 and 1977 Clean Air Act Amendments

b. 1990 Clean Air Act Amendments

i. 1-hour Ozone NAAQS

ii. Revised Ozone NAAQS

iii. Provisions Concerning Transport of Ozone and Its Precursors

2. Regulatory Structure

a. March 2, 1995 Policy

b. OTAG

c. EPA's Transport SIP Call Regulatory Efforts

d. Revision of the Ozone NAAQS

e. Impacts of NOX Emissions

D. EPA's Proposed Analytical Approach

1. Process for Requiring Submission of Section 110(a)(2)(D) SIP

Revisions

2. Overview of Elements of Section 110(a)(2)(D)

a. Summary of Section 110(a)(2)(D)

b. Significant Contribution to Nonattainment

c. Interfere with Maintenance

d. Remedying the Significant Contribution

i. Adequate Mitigation

ii. Elimination of Contribution

iii. Comparison of the Two Legal Interpretations of Section

110(a)(2)(D)

iv. Other Issues

e. Control Implementation and Budget Attainment Dates

E. Section 126 Petitions

F. OTAG Process

II. Weight of Evidence Determination of Significant Contribution

A. Introduction

B. Background Technical Information

1. OTAG Modeling Process

2. OTAG Strategy Modeling

3. OTAG Geographic Modeling

4. Other Relevant Analyses

C. Technical Analyses of Significant Contribution

1. Criteria for Determining Significant Contribution

2. Overview of Technical Approach

3. Identification of Ozone ``Problem Areas'

4. Analysis of Air Quality, Trajectory, and Non-OTAG Modeling

Information

5. Approaches for Analyzing Subregional Modeling Data

a. Approaches for 1-Hour Nonattainment

b. Approaches for 8-Hour Nonattainment

c. Methods for Presenting 1-Hour and 8-Hour Assessments

6. Contributions to 1-Hour Nonattainment

7. Contributions to 8-Hour Nonattainment

8. Assessment of State Contributions

D. Comparison of Upwind and Downwind Contributions to

Nonattainment and Costs of Controls

III. Statewide Emissions Budgets

A. General Approach for Calculating Budgets

1. Overview

2. Relationship of Proposed Budget Approach to the OTAG

Recommendations

3. Uniform Application of Control Measures

a. OTAG

b. Collective Contribution and Equity Considerations

c. Modeling Assumptions and Potential Synergistic Effects

d. Electrical Generation and Emissions Shifting

e. Alternative Approaches Based on Non-Uniform Application of

Control Measures

4. Seasonal vs Annual Controls

5. Consideration of Areas with CAA Section 182(f) NOX

Waivers

6. Relation of OTC NOX MOU to Budgets in the Ozone

Transport SIP Rulemaking

B. Budget Development Process

1. Overview

2. Description of and Rationale for Proposed Control Assumptions

a. Considering the Cost Effectiveness of Other Actions

b. Determining the Cost Effectiveness of NOX Controls

c. Summary of Measures Assumed in Proposed Budget Calculation

3. Proposed Assumptions for Electric Utilities

a. Affected Entities

b. Methodology Used to Determine the Proposed Electric Utility

Budget Component

i. Proposed Utility Budget Component Calculation and

Alternatives

ii. Seasonal Utilization

iii. Growth Considerations

c. Summary and Proposed Utility Budget Components

4. Proposed Assumptions for Other Stationary Sources

a. Affected Entities

b. Methodology Used to Determine the Proposed Area and

Nonutility Point Source Budget Components

c. Summary and Proposed Area and Nonutility Point Source Budget

Components

5. Proposed Assumptions for Highway Vehicles

a. Affected Entities

b. Methodology Used to Develop the Proposed Highway Vehicle

Budget Component

i. Budget Component Determination Method and Alternatives

Considered

ii. Activity Level Projections and Growth Considerations

iii. Seasonal/Weekday/Weekend Adjustment

iv. Comparison to OTAG Recommendations

c. Summary and Proposed Highway Vehicles Budget Components

d. Conformity

6. Proposed Assumptions for Nonroad Sources

a. Affected Entities

b. Methodology Used to Determine the Proposed Nonroad Budget

Component

i. Budget Component Determination Method and Alternatives

Considered

ii. Activity Level Projections and Growth Considerations

iii. Seasonal/Weekday/Weekend Adjustment

iv. Comparison to OTAG Recommendations

c. Summary and Proposed Nonroad Budget Components

C. State-by-State Emissions Budgets

D. Recalculation of Budgets

IV. Implementation of Revised Air Quality Standards

A. Introduction

B. Background

C. Implementation Policy

1. Areas Eligible for the Transitional Classification

2. Areas Not Eligible for the Transitional Classification

V. SIP Revisions and Approvability Criteria

A. SIP Revision Requirements and Schedule

B. SIP Approval Criteria

1. Budget Demonstration

2. Control Strategies

a. Enforceable Measures Approach

b. Fixed Tonnage Budgets

3. Control Strategy Implementation

4. Growth Estimates

5. Promoting End-Use Energy Efficiency

C. Review of Compliance

D. 2007 Reassessment of Transport

E. Sanctions

1. Failure to Submit

2. Failure to Implement

F. Federal Implementation Plans (FIPs)

1. Legal Framework

2. Timing of FIP Action

3. Statewide Emissions Budgets

4. FIP Control Measures

5. FIP Trading Program

6. Section 105 Grants

G. Other Consequences

VI. States Not Covered by This Rulemaking

VII. Model Cap-and-Trade Program

VIII. Regulatory Analysis

IX. Air Quality Analyses

X. Nonozone Benefits of NOX Reductions

XI. Impact on Small Entities

XII. Unfunded Mandates Reform Act

Appendix A--References

Appendix B--OTAG Recommendations

Appendix C--Tables for Section II. Weight of Evidence

Determination of Significant Contribution

Appendix D--Figures for Section II. Weight of Evidence

Determination of Significant Contribution

I. Preamble

A. Summary of Rulemaking and Affected States

The CAA has set forth many requirements to address nonattainment of

the ozone NAAQS. Many States have found it difficult to demonstrate

attainment of the NAAQS due to the widespread transport of ozone and

its precursors. The Environmental Council of the States (ECOS)

recommended formation of a national work group to allow for a

thoughtful assessment and development of consensus solutions to the

problem. This work group, OTAG, was established 2 years ago to

undertake an assessment of the regional transport problem in the

Eastern half of the United States. The OTAG was a collaborative process

conducted by representatives from the affected States, EPA, and

interested members of the

[[Page 60320]]

public, including environmental groups and industry, to evaluate the

ozone transport problem and develop solutions. The OTAG region includes

the following 37 States and the District of Columbia: Alabama,

Arkansas, Connecticut, Delaware, District of Columbia, Florida,

Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine,

Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri,

Nebraska, New Hampshire, New Jersey, New York, North Carolina, North

Dakota, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina,

South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia and

Wisconsin. Today's action builds on the work of OTAG.

Through the OTAG process, the States concluded that widespread

NOX reductions are needed in order to enable areas to attain

and maintain the ozone NAAQS. The EPA believes, based on data generated

by OTAG and other data sources, that certain downwind States receive

amounts of transported ozone and ozone precursors that significantly

contribute to nonattainment in the downwind States. Today's action

proposes SIP requirements under section 110(a)(1) and section 110(k)(5)

in order to meet the requirements of section 110(a)(2)(D) to prohibit

ozone precursor emissions from sources or activities in those States

from ``contribut(ing) significantly to nonattainment in, or

interfer(ing) with maintenance by,'' a downwind State of the ozone

NAAQS.

Upon this determination, the EPA is requiring SIP revisions in

order to take steps toward ensuring that the necessary regional

reductions are achieved that will enable current ozone nonattainment

areas in the eastern half of the United States to prepare attainment

demonstrations and that will enable all areas to demonstrate

noninterference with maintenance of the ozone standard.

The OTAG's July 8, 1997 final recommendations (see Section I.F.

OTAG Process and Appendix B) identify control measures for States to

achieve additional reductions in emissions of NOX and do not

identify such measures for volatile organic compounds (VOC) beyond

EPA's promulgation of national VOC measures. The OTAG Regional and

Urban Scale Modeling and Air Quality Analysis Work Groups reached the

following relevant conclusions:

Regional NOX emissions reductions are effective

in producing ozone benefits; the more NOX reduced, the

greater the benefit.

VOC controls are effective in reducing ozone locally and

are most advantageous to urban nonattainment areas. (See Appendix B).

The EPA agrees with these OTAG conclusions and, thus, is not

proposing new SIP requirements for VOC emissions for the purpose of

reducing the interstate transport of ozone. States may, however, need

to consider additional reductions in VOC emissions as they develop

local plans to attain and maintain the ozone standards.

Therefore, this rulemaking is intended to make a finding of

significant contribution to a nonattainment problem, or interference

with a maintenance problem, and to assign, specifically, the emissions

budgets for NOX that each of the identified States must meet

through SIP measures. As indicated, the EPA is proposing to require the

submission of SIP controls to meet the specified budgets. However, this

requirement permits each State to choose for itself what measures to

adopt to meet the necessary emission budget. Consistent with OTAG's

recommendations to achieve NOX emission decreases primarily

from large stationary sources in a trading program, EPA encourages

States to consider electric utility and large boiler controls under a

cap-and-trade program as a cost-effective strategy. This is described

in more detail in section III, Statewide Emission Budgets. The EPA also

recognizes that promotion of energy efficiency can contribute to a

cost-effective strategy. The EPA is working to develop guidance on how

States can integrate energy efficiency into their SIPs to help meet

their NOX budgets at least cost.

The EPA proposes to find, after considering OTAG's recommendations

and other relevant information, that the following 22 States and the

District of Columbia significantly contribute to nonattainment in, or

interfere with maintenance by, a downwind State: Alabama, Connecticut,

Delaware, Georgia, Illinois, Indiana, Kentucky, Massachusetts,

Maryland, Michigan, Missouri, North Carolina, New Jersey, New York,

Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia,

West Virginia, and Wisconsin. These findings proposed today reflect the

air quality modeling and other technical work done by OTAG, as well as

other relevant information.

Under this proposal, these States would be required to adopt and

submit, within 12 months after publication of the notice of final

rulemaking, SIPs containing control measures that will mitigate the

ozone transport problem by meeting the assigned statewide emissions

budget. Section II, Weight of Evidence Determination of Significant

Contribution, describes how EPA determined which States to propose as

significant contributors, and section III, Statewide Emission Budgets,

describes how EPA determined the appropriate statewide emission budgets

and proposes to assign specific emission budgets for the States

identified above. Section V, SIP Revisions and Approvability Criteria,

describes the proposed SIP requirements.

The EPA believes that expedited implementation of regional control

strategies to facilitate attainment is necessary. On July 18, 1997, EPA

published its final rule for strengthening the NAAQS for ozone by

establishing a new, 8-hour NAAQS (62 FR 38856). This results in more

areas and larger areas with monitoring data indicating nonattainment.

Thus, it will be even more critical to implement regional control

strategies which will mitigate transport into areas in violation of the

new standard and thus enable these areas to demonstrate attainment. The

regional NOX reduction strategy proposed in today's action

will provide a mechanism to achieve reductions that will be necessary

for States to enable them to attain and maintain this revised standard.

The proposed regional reductions alone should be enough to allow most

of the new nonattainment counties in States covered by this rulemaking

to be able to comply with the new standard. States that are not

required to comply with the requirements set forth in today's action

would also benefit from the NOX strategy EPA is proposing if

they adopt similar measures. On July 16, 1997, President Clinton issued

a directive on the implementation of the revised air quality standards.

This implementation policy is described in section IV, Implementation

of Revised Air Quality Standards.

Many of the States that EPA is not proposing to find as significant

contributors to the ozone nonattainment problem, and, therefore, do not

have a proposed NOX statewide emissions budget to mitigate

ozone transport, still may need, as recommended by OTAG, to cooperate

and coordinate SIP development activities with other States. States

with local interstate nonattainment areas for the 1-hour standard and/

or the new 8-hour standard are expected to work together to reduce

emissions to mitigate local scale interstate transport problems in

order to provide for attainment in the nonattainment area as a whole.

In addition, areas in these States (those covered by OTAG modeling

but

[[Page 60321]]

not covered by this proposal) may be able to receive the transitional

classification as described in section IV, Implementation of Revised

Air Quality Standards. An area in the State would satisfy one of the

eligibility requirements for the transitional area classification by

attaining the 1-hour standard and submitting a SIP attainment

demonstration by 2000 for the 8-hour standard. The OTAG's modeling (in

particular, OTAG strategy Run 5 described in section II.B.2, OTAG

Strategy Modeling) shows that a strategy in which a State adopted

NOX emission decreases similar to those EPA proposes to

establish in this rulemaking would be helpful in achieving attainment

in most of these areas. The EPA strongly suggests that these States

(those covered by OTAG modeling but not covered by this proposal) with

new nonattainment counties for the 8-hour standard should consider the

option of this strategy since our analysis indicates that nearly all

new nonattainment counties are projected to come into attainment as a

result of this strategy. The benefits of this regional strategy for

States not required to implement the proposed strategy under this

rulemaking are described below in section VI, States Not Covered by

this Rulemaking.

The EPA plans to publish a supplemental notice of proposed

rulemaking (SNPR) in early 1998. The Agency intends to include in the

SNPR a proposed model cap-and-trade rule, air quality analyses of the

proposed statewide emission budgets, emissions reporting and State

reporting requirements, a discussion of the interaction with the Title

IV NOX rule (including EPA's plans to proceed with

rulemaking on remanded elements of that rule relating to flexible

implementation where an appropriate cap-and-trade system is in place),

and proposed rule language for the rulemaking discussed in today's

action. There will be another public comment period following

publication of the SNPR. All comments received regarding either today's

action or the proposed rule language in the SNPR will be considered

before promulgation of a final rule.

B. General Factual Background

In today's proposal, EPA takes a significant step in order to

reduce ozone in the eastern half of the country. Ground-level ozone,

the main harmful ingredient in smog, is produced in complex chemical

reactions when its precursors, VOC and NOX, react in the

presence of sunlight. The chemical reactions that create ozone take

place while the pollutants are being blown through the air by the wind,

which means that ozone can be more severe many miles away from the

source of emissions than it is at the source.

At ground level, ozone can cause a variety of ill effects to human

health, crops and trees. Specifically, ground-level ozone induces the

following health effects:

Decreased lung function, primarily in children active

outdoors.

Increased respiratory symptoms, particularly in highly

sensitive individuals.

Hospital admissions and emergency room visits for

respiratory causes, among children and adults with pre-existing

respiratory disease such as asthma.

Inflammation of the lung.

Possible long-term damage to the lungs.

The new 8-hour primary ambient air quality standard will provide

increased protection to the public from these health effects.

Each year, ground-level ozone above background is also responsible

for several hundred million dollars worth of agricultural crop yield

loss. It is estimated that full compliance of the newly promulgated

ozone NAAQS will result in about $500 million of prevented crop yield

loss. Ozone also causes noticeable foliar damage in many crops, trees,

and ornamental plants (i.e., grass, flowers, shrubs, and trees) and

causes reduced growth in plants. Studies indicate that current ambient

levels of ozone are responsible for damage to forests and ecosystems

(including habitat for native animal species).

The science of ozone formation, transport, and accumulation is

complex. Ozone is produced and destroyed in a cyclical set of chemical

reactions involving NOX, VOC and sunlight. Emissions of

NOX and VOC are necessary for the formation of ozone in the

lower atmosphere. In part of the cycle of reactions, ozone

concentrations in an area can be lowered by the reaction of nitric

oxide with ozone, forming nitrogen dioxide; as the air moves downwind

and the cycle continues, the nitrogen dioxide forms additional ozone.

The importance of this reaction depends, in part, on the relative

concentrations of NOX, VOC and ozone, all of which change

with time and location.

As part of the efforts to reduce harmful levels of smog, EPA today

proposes to require certain States to revise their SIPs in order to

implement the regional reductions in transported ozone and its

precursors that are needed to enable areas in the Eastern United States

to attain and maintain the NAAQS. Since air pollution travels across

county and State lines, it is essential for State governments and air

pollution control agencies to cooperate to solve the problem.

C. Statutory and Regulatory Background

1. Clean Air Act Provisions

a. 1970 and 1977 Clean Air Act Amendments. For almost 30 years,

Congress has focused major efforts on curbing tropospheric ozone. In

1970, Congress amended title I of the CAA to require, among other

things, that EPA issue, and periodically review and if necessary

revise, NAAQS for ubiquitous air pollutants (sections 108 and 109).

Congress required the States to submit SIPs to attain those NAAQS, and

Congress included, in section 110, a list of minimum requirements that

SIPs must meet. Congress anticipated that areas would attain the NAAQS

by 1975.

In 1977, Congress amended the CAA to provide, among other things,

additional time for areas to attain the ozone NAAQS, as well as to

impose specific SIP requirements for those nonattainment areas. These

provisions first required the designation of areas as attainment,

nonattainment, or unclassified, under section 107; and then required

that SIPs for ozone nonattainment areas include the additional

provisions set out in part D of title I, as well as demonstrations of

attainment of the ozone NAAQS by either 1982 or 1987 (section 172).

In addition, the 1977 Amendments included two provisions focused on

interstate transport of air pollutants: the predecessor to current

section 110(a)(2)(D), which requires SIPs for all areas to constrain

emissions with certain adverse downwind effects; and section 126, which

authorizes a downwind State (or political subdivision) to petition for

EPA to impose limits directly on upwind sources found to adversely

affect that State. Section 110(a)(2)(D), which is key to the present

action, is described in more detail below.

b. 1990 Clean Air Act Amendments. In 1990, Congress amended the CAA

to better address, among other things, continued nonattainment of the

1-hour ozone NAAQS, the requirements that would apply if EPA revised

the 1-hour standard, and transport of air pollutants across State

boundaries (Pub. L. 101-549, Nov. 15, 1990, 104 Stat. 2399, codified at

42 U.S.C. 7401-7671q). Numerous provisions added, or revised, by the

1990 Amendments are relevant to today's proposal.

[[Page 60322]]

i. 1-hour Ozone NAAQS. In the 1990 Amendments, Congress required

the States and EPA to review and, if necessary, revise the designation

of areas as attainment, nonattainment, and unclassifiable under the

ozone NAAQS in effect at that time, which was the 1-hour standard

(section 107(d)(4)). Areas designated as nonattainment were divided

into, primarily, five classifications based on air quality design value

(section 181(a)(1)). Each classification carries specific requirements,

including new attainment dates (sections 181-182). In increasing

severity of the air quality problem, these classifications are

marginal, moderate, serious, severe and extreme. The OTAG region

includes all classifications except extreme.

As amended in 1990, the CAA requires States containing ozone

nonattainment areas classified as serious, severe, or extreme to submit

several SIP revisions at various times. One set of SIP revisions

included specified control measures, such as reasonably available

control technology (RACT) for existing VOC and NOX sources

(section 182(b)(2), 182(f)). In addition, the CAA requires the

reduction of VOC in the amount of 15 percent by 1996 from a 1990

baseline (section 182(b)(1)). Further, the CAA requires the reduction

of VOC or NOX emissions in the amount of 9 percent over each

3-year period from 1996 through the attainment date (the rate-of-

progress (ROP) SIP submittals) under section 182(c)(2)(B). In addition,

the CAA requires a demonstration of attainment (including air quality

modeling) for the nonattainment area (the attainment demonstration), as

well as SIP measures containing any additional reductions that may be

necessary to attain by the applicable attainment date (section 182(c)-

(e)). The CAA established November 15, 1994 as the required date for

the ROP and attainment demonstration SIP submittals.1

---------------------------------------------------------------------------

\1\ For moderate ozone nonattainment areas, the attainment

demonstration was due November 15, 1993 (section 182(b)(1)(A),

except that if the State elected to conduct an urban airshed model,

EPA allowed an extension to November 15, 1994.

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ii. Revised Ozone NAAQS. Section 109(d) of the CAA requires

periodic review and, if appropriate, revision of the NAAQS. As amended

in 1990, the CAA further requires designating areas as attainment,

nonattainment, and unclassifiable under a revised NAAQS (section

107(d)(1)). The CAA authorizes EPA to classify areas that are

designated nonattainment under a new NAAQS, and to establish for those

areas attainment dates not to exceed 10 years from the date of

designation (section 172(a)).

The CAA continues, in revised form, certain requirements, dating

from the 1970 Amendments, which pertain to all areas, regardless of

their designation. All areas are required to submit SIPs within certain

time frames (section 110(a)(1)), and those SIPs must include specified

provisions, under section 110(a)(2). In addition, SIPs for

nonattainment areas are generally required to include additional

specified control requirements, as well as controls providing for

attainment of the revised NAAQS and periodic reductions providing

``reasonable further progress'' in the interim (section 172(c)).

iii. Provisions Concerning Transport of Ozone and Its Precursors.

The 1990 Amendments reflect general awareness by Congress that ozone is

a regional, and not merely a local, problem. As described above, ozone

and its precursors may be transported long distances across State lines

to combine with ozone and precursors downwind, thereby exacerbating the

ozone problems downwind. In the case of ozone, this transport

phenomenon was not generally recognized until relatively recently. Yet,

ozone transport is a major reason for the persistence of the ozone

problem, notwithstanding the imposition of numerous controls, both

Federal and State, across the country.

Section 110(a)(2)(D) provides one of the most important tools for

addressing the problem of transport. This provision, which applies by

its terms to all SIPs for each pollutant covered by a NAAQS, and for

all areas regardless of their attainment designation, provides that a

SIP must contain provisions preventing its sources from contributing

significantly to nonattainment problems or interfering with maintenance

in downwind States.

Section 110(k)(5) authorizes EPA to find that a SIP is

substantially inadequate to meet any CAA requirement, as well as to

mitigate interstate transport of the type described in section 184

(concerning ozone transport in the northeast) or section 176A

(concerning interstate transport in general) and thereby require the

State to submit, within a specified period, a SIP revision to correct

the inadequacy. The CAA further addresses interstate transport of

pollution in section 126, which Congress clarified in 1990.

Subparagraph (b) of that provision authorizes each State (or political

subdivision) to petition EPA for a finding that emissions from ``any

major source or group of stationary sources'' in an upwind State

contribute significantly to nonattainment in, or interfere with

maintenance by, the downwind State. If EPA makes such a finding in

support of a section 126 petition, EPA would impose limits on the

affected source or group of sources (section 126(c)).2

---------------------------------------------------------------------------

\2\ In addition, section 115 authorizes EPA to require a SIP

revision when a State's emitters ``cause or contribute to air

pollution which may reasonably be anticipated to endanger public

health or welfare in a foreign country.''

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In addition, the 1990 Amendments included specific provisions

focused on the interstate transport of ozone. Section 184 delineates a

multistate ozone transport region (OTR) in the Northeast, requires

specific additional controls for all areas (not only nonattainment

areas) in that region, and establishes the Ozone Transport Commission

(OTC) for the purpose of recommending to EPA regionwide controls

affecting all areas in that region.

2. Regulatory Structure

a. March 2, 1995 Policy. Notwithstanding significant efforts, the

States generally were not able to meet the November 15, 1994 statutory

deadline for the attainment demonstration and other SIP submissions

required under section 182(c). The major reason for this failure was

that States were not able to address or control transport. As a result,

in a memorandum from Mary D. Nichols, Assistant Administrator for Air

and Radiation, dated March 2, 1995, entitled ``Ozone Attainment

Demonstrations,'' (March 2, 1995 Memorandum or the Memorandum), EPA

recognized the efforts made by States and the remaining difficulties in

making the ROP and attainment demonstration submittals. The EPA

recognized that development of the necessary technical information, as

well as the control measures necessary to achieve the large level of

reductions likely to be required, had been particularly difficult for

the States affected by ozone transport.

Accordingly, as an administrative remedial matter, the Memorandum

indicated that EPA would establish new time frames for SIP submittals.

The Memorandum indicated that EPA would divide the required SIP

submittals into two phases. Phase I generally consisted of: SIP

measures providing for ROP reductions due by the end of 1999, an

enforceable SIP commitment to submit any remaining required ROP

reductions on a specified schedule after 1996, and an enforceable SIP

commitment to submit the additional SIP measures needed for attainment.

Phase II consists of the remaining submittals, beginning in 1997.

Ten States and the District of Columbia failed to submit Phase I

[[Page 60323]]

elements within the specified time. By notice dated July 10, 1996 (61

FR 36292), EPA issued findings and thereby started sanctions clocks for

these areas for those Phase I submittals.

The Phase II submittals primarily consisted of the remaining ROP

SIP measures, the attainment demonstration and additional local rules

needed to attain, and any regional controls needed for attainment by

all areas in the region. The March 2, 1995 Memorandum indicated that

the attainment demonstration, target calculations for the post-1999 ROP

milestones, and identification of rules needed to attain and for post-

1999 ROP were due in mid-1997. To allow time for States to incorporate

the results of the OTAG modeling into their local plans, EPA, in its

Final Policy for Implementation of the 1-hour and Pre-Existing PM-10

Standards, is extending the mid-1997 submittal date to April 1998.

b. OTAG. In addition, the March 2 1995 Memorandum called for an

assessment of the ozone transport phenomenon. The Environmental Council

of States (ECOS) had recommended formation of a national work group to

allow for a thoughtful assessment and development of consensus

solutions to the problem. The OTAG has been a partnership between EPA,

the 37 easternmost States and the District of Columbia, industry

representatives and environmental groups. This effort has created an

opportunity for the development of an Eastern United States ozone

strategy to address transport and to assist in attainment of the 1-hour

ambient ozone standard.

The EPA believes that the OTAG process has been invaluable in

demonstrating the types of regional ozone precursor reductions that are

needed to enable areas in the Eastern United States to attain and

maintain the ambient air quality standard for ozone. Indeed, today's

action to propose to mandate SIP revisions under section 110(a)(2)(D)

is a first step directed at providing the regulatory structure to

implement the kinds of broad regional precursor reductions recommended

by OTAG.

c. EPA's Transport SIP Call Regulatory Efforts. Shortly after OTAG

began its work, EPA began to indicate that it intended to issue a SIP

call to require States to implement the reductions necessary to address

the ozone transport problem. On January 10, 1997 (62 FR 1420), EPA

published a Notice of Intent that articulated this goal and indicated

that before taking final action, EPA would carefully consider the

technical work and any recommendations of OTAG.

By a letter to Mary Gade, Chair of OTAG, dated April 16, 1997, EPA

Assistant Administrator Mary D. Nichols stated that on the basis of

technical work performed by EPA staff, it appeared that EPA would issue

a SIP call to specified States and the District of Columbia. The EPA

staff issued a technical support document, ``Preliminary Assessment of

States Making a Significant Contribution to Downwind Ozone

Nonattainment,'' dated April, 1997, which explained EPA's technical

basis for those tentative conclusions. Please refer to section II,

Weight of Evidence Determination of Significant Contribution, for EPA's

revised conclusions.

As described below in section I.F., OTAG Process, OTAG completed

its work in June 1997 and issued its final recommendations to EPA on

July 8, 1997. The OTAG's technical work and recommendations form part

of the basis of today's proposal.

d. Revision of the Ozone NAAQS. On July 18, 1997 (62 FR 38856), EPA

issued its final action to revise the NAAQS for ozone. The EPA's

decision to revise the standard was based on the Agency's review of the

available scientific evidence linking exposures to ambient ozone to

adverse health and welfare effects at levels allowed by the pre-

existing 1-hour ozone standards. The 1-hour primary standard was

replaced by an 8-hour standard at a level of 0.08 parts per million

(ppm), with a form based on the 3-year average of the annual fourth-

highest daily maximum 8-hour average ozone concentration measured at

each monitor within an area. The new primary standard will provide

increased protection to the public, especially children and other at-

risk populations, against a wide range of ozone-induced health effects.

Health effects are described in section I.B, General Factual

Background. The EPA retained the applicability of the 1-hour NAAQS for

certain areas to ensure adequate health protection during the

transition to full implementation of the 8-hour NAAQS.

The pre-existing 1-hour secondary ozone standard was replaced by an

8-hour standard identical to the new primary standard. The new

secondary standard will provide increased protection to the public

welfare against ozone-induced effects on vegetation as described in

section I.B, General Factual Background.

e. Impacts of NOX Emissions. At the August 7, 1997 Clean

Air Act Advisory Committee meeting, EPA announced the availability of a

document (``Nitrogen Oxides: Impacts on Public Health and the

Environment,'' EPA-452/R-97-002, August 1997) that describes the

multiple impacts of NOX emissions on public health and the

environment and the consequent implications for national policy. In

addition to helping attain public health standards for ozone, decreases

in emissions of NOX are helpful to reducing acid deposition,

greenhouse gases, nitrates in drinking water, stratospheric ozone

depletion, excessive nitrogen loadings to aquatic and terrestrial

ecosystems, and ambient concentrations of nitrogen dioxide, particulate

matter and toxics. These impacts are described in more detail in

section X, Nonozone Benefits of NOX Reductions.

D. EPA's Proposed Analytical Approach

1. Process for Requiring Submission of Section 110(a)(2)(D) SIP

Revisions

As described above, SIPs for all areas must meet the requirements

of section 110(a)(2), including section 110(a)(2)(D), which imposes

limits on sources that affect the ability of downwind areas to attain

and maintain the NAAQS. Because many areas are currently required to

attain two ozone NAAQS--the 1-hour standard and the 8-hour standard--

with different SIP planning requirements, EPA proposes that section

110(a)(2)(D) be applied in different ways with respect to each of the

ozone NAAQS.

Under the 1-hour ozone NAAQS, each area is currently required to

have a SIP in place. Moreover, EPA has determined that the 1-hour

standard will continue to apply to areas designated nonattainment for

the 1-hour NAAQS until EPA determines that the area has air quality

meeting this standard (40 CFR 50.9(a) (62 FR 38894 (July 18, 1997)).

Accordingly, each area is under a current obligation to include in its

SIP, provisions that meet the requirements of section 110(a)(2)(D) for

the 1-hour NAAQS.

This obligation to meet section 110(a)(2)(D) under the 1-hour

standard applies even after EPA determines that an upwind area has

attained the 1-hour standard, and the applicability of that standard

thereby terminates for the upwind area. Regardless of the status of the

1-hour standard with respect to the upwind area's air quality, a

downwind area may continue to have a nonattainment problem under the 1-

hour standard, and the upwind area's sources may continue to impact

that downwind nonattainment problem. Under these circumstances, the

upwind area would be required to retain or adopt SIP provisions that

meet the requirements of section 110(a)(2)(D).

[[Page 60324]]

To assure that SIPs include required controls, section 110(k)(5)

authorizes EPA to find that a SIP is substantially inadequate to meet

an CAA requirement, and to require (``call for'') the State to submit,

within a specified period, a SIP revision to correct the inadequacy.

This EPA requirement for a SIP revision is known as a ``SIP call.''

Specifically, section 110(k)(5) provides, in relevant part:

Whenever the Administrator finds that the applicable

implementation plan for any area is substantially inadequate to

attain or maintain the relevant [NAAQS], to mitigate adequately the

interstate pollutant transport described in section 176A or section

184, or to otherwise comply with any requirement of this Act, the

Administrator shall require the State to revise the plan as

necessary to correct such inadequacies. The Administrator shall

notify the State of the inadequacies, and may establish reasonable

deadlines (not to exceed 18 months after the date of such notice)

for the submission of such plan revisions.

By today's action, EPA is proposing to determine that the SIPs

under the 1-hour ozone NAAQS for the States identified in today's

action are substantially inadequate to comply with the requirements of

section 110(a)(2)(D) and to mitigate adequately the regional,

interstate ozone transport described in section 184, because ozone

precursor emissions and transported ozone from those States contribute

significantly to nonattainment downwind. Based on these findings, EPA

today proposes a SIP call to require the identified States to reduce

emissions to mitigate their contribution.

If a State fails to submit the required SIP provisions in response

to this SIP call, EPA is required to issue a finding that the State

failed to make a required SIP submittal under section 179(a). This

finding has implications for sanctions as well as EPA's promulgation of

a Federal implementation plan (FIP). Sanctions and a FIP are discussed

in section V., SIP Revisions and Approvability Criteria.

Under the 8-hour ozone NAAQS, areas have not yet been designated as

attainment, nonattainment, or unclassifiable, and are not yet required

to have SIPs in place. When those SIPs become due, they must meet the

applicable requirements of section 110, which apply to all areas, and

SIPs for areas designated nonattainment must also meet the additional

requirements in subpart 1 of part D applicable to nonattainment areas.

Section 110(a)(1) provides, in relevant part--

Each State shall * * * adopt and submit to the Administrator,

within 3 years (or such shorter period as the Administrator may

prescribe) after the promulgation of a national primary ambient air

quality standard (or any revision thereof) * * * a plan which provides

for implementation, maintenance, and enforcement of such primary

standard in each (area) within such State.

Section 110(a)(2) provides, in relevant part--

Each implementation plan submitted by a State under this CAA

shall be adopted by the State after reasonable notice and public

hearing. Each such plan shall (meet certain requirements, including

those found in section 110(a)(2)(D)).

These two provisions, read together, require SIP revisions under

the revised NAAQS within 3 years of the date of the revision, or

earlier if EPA so requires, and require that those SIP revisions meet

the requirements of section 110(a)(2), including subparagraph (D). It

should be noted that the schedule for these section 110(a)(2) SIP

submissions for all ozone areas differs from the schedule for the SIP

submissions required under section 172(b) for part D SIP submissions

for ozone nonattainment areas. These part D SIP submissions are

required for all areas that are designated nonattainment under the 8-

hour NAAQS and must be submitted within 3 years of the date of

designation. The submission of SIP revisions containing the regional

NOX reductions proposed under this rulemaking earlier than

the part D nonattainment submissions will assist the downwind

nonattainment areas in their attainment planning.

The EPA believes it has the authority to establish different

submittal schedules for different parts of the section 110(a)(1) SIP

revision. Specifically, EPA proposes to require first the portion of

the section 110(a)(1) SIP revision that contains the controls required

under section 110(a)(2)(D). The EPA proposes to require the section

110(a)(2)(D) submittal first for the purpose of securing upwind

reductions at an earlier stage in the regional SIP planning process.

This information on controls in upwind States is essential to the

downwind States in the latter States' attainment planning.

In summary, EPA is proposing to determine, under section 110(k),

that the 1-hour ozone NAAQS SIPs for certain States are deficient

because the SIPs do not impose sufficient controls on their sources to

meet the requirements of section 110(a)(2)(D), and EPA is proposing to

require those States to submit SIP revisions containing adequate

controls. The EPA is proposing to require, under section 110(a)(1),

that certain States must submit SIP revisions under the 8-hour ozone

NAAQS to meet the requirements of section 110(a)(2)(D). For simplicity,

today's rulemaking occasionally uses the term ``SIP call'' to describe

both EPA actions.

2. Overview of Elements of Section 110(a)(2)(D)

a. Summary of Section 110(a)(2)(D). As noted above, section

110(a)(2)(D) is the operative provision for determining whether

additional controls are required to mitigate the impact of upwind

sources on downwind air quality, with respect to both the 1-hour and 8-

hour ozone NAAQS. Separate determinations must be made for each NAAQS.

Section 110(a)(2)(D) provides, in relevant part, that each SIP

must:

* * * contain adequate provisions * * * prohibiting, consistent with

the provisions of this title, any source or other type of emissions

activity within the State from emitting any air pollutant in amounts

which will * * * contribute significantly to nonattainment in, or

interfere with maintenance by, any other State with respect to any

such national primary or secondary ambient air quality standard * *

*.

According to section 110(a)(2)(D), the SIP for each area,

regardless of its designation as nonattainment or attainment (including

unclassifiable), must prohibit sources within the area from emitting

emissions that: ``contribute significantly'' to ``nonattainment'' in a

downwind State, or that ``interfere with maintenance'' in a downwind

State.

b. Significant Contribution to Nonattainment. The initial prong

under section 110(a)(2)(D) is whether sources ``contribute

significantly'' to ``nonattainment in * * * any other State'' with

respect to the NAAQS. The initial inquiry for this prong is to identify

and determine the geographic scope of ``nonattainment'' downwind. The

EPA proposes to interpret this term to refer to air quality and not to

be limited to currently-designated nonattainment areas. Section

110(a)(2)(D) does not refer to ``nonattainment areas,'' which is a

phrase that EPA interprets to refer to areas that are designated

nonattainment under section 107 (section 107(d)(1)(A)(I)). Rather, the

provision includes only the term ``nonattainment'' and does not define

that term. Under these circumstances, EPA has discretion to give the

term a reasonable definition, and EPA proposes to define it to include

areas whose air quality currently violates the NAAQS, and will likely

continue for some time to violate,

[[Page 60325]]

regardless of the designation of those areas (compare section

181(b)(2)(A) (referring to ozone ``nonattainment area'' which EPA

interprets as an area designated nonattainment) and section

211(k)(10)(D)).

For present purposes, EPA is examining the air quality for the

1993-1995 years, but EPA expects to refer to 1996 (and perhaps 1997)

data as the rulemaking proceeds.

As discussed below, to determine whether emissions from sources in

an upwind area significantly contribute to nonattainment downwind, EPA

proposes to compare NOX emissions reductions upwind with

ozone reductions downwind. For this purpose, EPA assumes that areas

with current air quality indicating nonattainment for the 1-hour

standard will be required to implement certain controls under the CAA,

through the year 2007, which is the attainment date for ozone

nonattainment areas classified as severe-17. Accordingly, EPA proposes

to determine, through air quality modeling, which areas with current

air quality indicating nonattainment for both the 1-hour and 8-hour

standards will continue to be in nonattainment in the year 2007, even

after implementation of controls specifically required under the CAA.

Because this projection is occurring through the year 2007, it is also

necessary to take into account growth in emissions, generally due to

economic growth and greater use of vehicles, to that time. If an area

with air quality currently indicating nonattainment is modeled to

continue to be in nonattainment as of the year 2007, then emissions

from sources in upwind areas may be considered to ``contribute

significantly'' to the current nonattainment problem, depending on the

factors described below. On the other hand, if an area the current air

quality of which measures nonattainment is modeled to be in attainment

in the year 2007 due to imposition of required CAA controls, then EPA

proposes not to consider emissions from sources in upwind areas to

``contribute significantly'' to that downwind area.

The EPA's decision is explained below for choosing the year 2007 as

the date for assuming the implementation of controls and for modeling

air quality.

The EPA proposes a similar analysis for purposes of the 8-hour

NAAQS. The EPA will consider as ``nonattainment'' any area that has

monitored nonattainment air quality currently, and for which modeling

shows is likely to continue to be in nonattainment in the year 2007

after application of controls specifically required under the CAA.

After determining the scope of the downwind nonattainment problem,

EPA must next analyze whether the emissions from sources in the upwind

area ``contribute significantly'' to the nonattainment problem. As

described below, EPA analyzed all NOX emissions in specified

upwind areas, made proposed determinations as to significant

contributions based on the entire inventory of the area's

NOX emissions and is requiring SIP revisions that address

overall levels of NOX emissions. By contrast, EPA is not, in

this rulemaking, determining whether particular sectors of the

NOX inventory ``contribute significantly'' and is not

mandating controls on particular sectors of that inventory.

Neither the CAA nor its legislative history provides meaningful

guidance for interpreting the term, ``contribute significantly''

(H.Rept. 101-491, 101st Cong., 2d sess., 1990, 218). The simpler part

of the analysis concerns the term, ``contribute.'' In EPA's view, if

emissions have an impact on downwind nonattainment, those emissions

should be considered to contribute to the nonattainment problem.

Generally, because ozone is a secondary pollutant formed as a result of

complex chemical reactions, it is not possible to determine downwind

impact on a source-by-source basis. However, if air quality modeling

shows that the aggregation of emissions from a particular geographic

region affect a nonattainment problem, then all of the emissions in

that region should be considered as contributors to that nonattainment

problem.

Whether a contribution from sources in a particular upwind area is

``significant'' depends on the overall air quality context. The EPA is

proposing a ``weight of evidence'' test under which several factors are

considered together, but none of them individually constitutes a

bright-line determination.

The EPA is proposing and soliciting comment on two alternative

interpretations of section 110(a)(2)(D). Each of the two

interpretations relies on a set of factors to make the determinations

required under section 110(a)(2)(D). In addition, each of the two

relies on the same factors. However, each relies on different factors

in different parts of the analysis.

Under the first interpretation of section 110(a)(2)(D), the weight

of evidence test for determining significant contribution focuses on

factors concerning amounts of emissions and their ambient impact,

including the nature of how the pollutant is formed, the level of

emissions and emissions density (defined as amount of emissions per

square mile) in the particular upwind area, the level of emissions in

other upwind areas, the amount of contribution to ozone in the downwind

area from upwind areas, and the distance between the upwind sources and

the downwind nonattainment problem. Under this approach, when emissions

and ambient impact reach a certain level, as assessed by reference to

the factors identified above, those emissions would be considered to

``contribute significantly'' to nonattainment. The EPA would then

determine what emissions reductions must be required in order to

adequately mitigate these contributions. Evaluation of the costs of

available measures for reducing upwind emissions enters into this

determination, as well as to the extent known (at least qualitatively),

the relative costs of, amounts of emission reductions from, and ambient

impact of, measures available in the downwind areas. The EPA proposes

to require upwind areas to implement a NOX budget reflecting

cost-effective controls that compare favorably, at least qualitatively,

with the costs of controls downwind and that reduces ozone levels

downwind.

Under the second interpretation of section 110(a)(2)(D), the weight

of evidence test for determining significant contribution includes all

of the factors identified immediately above, including the factors that

comprise the adequate mitigation test. That is, the relevant factors

concern upwind emissions and ambient impact therefrom, as well as the

costs of the available measures for reducing upwind emissions and, to

the extent known (at least qualitatively), the relative costs of,

amounts of emissions reductions from, and ambient impact of measures

available in the downwind areas. Thus, under this second

interpretation, the cost effectiveness of controlling upwind emissions

would be an important, but not necessarily a controlling factor in

evaluating whether emissions meet the significant contribution test. As

a result, EPA may conclude that a certain amount of the upwind

emissions contributes significantly to downwind problems because, among

other things, that amount may be eliminated through controls that are

relatively more cost effective. However, EPA would not conclude that

the remaining emissions contribute significantly because the additional

available controls that might be implemented are not as cost effective.

Under this second interpretation, once EPA determines what amount of

emissions contribute significantly to problems downwind, the remedy

would be for EPA to require the elimination of

[[Page 60326]]

that amount of upwind emissions and to determine the NOX

budgets accordingly.

Under either the first or second interpretation of section

110(a)(2)(D), EPA would be considering the relative costs and cost

effectiveness of various controls in deciding how much each State would

need to reduce its emissions. The methodology EPA would employ to reach

this result under either interpretation is set forth more fully in

sections II and III of today's action.

As discussed above, unhealthful levels of ozone result from

emissions of NOX and VOC from thousands of stationary

sources and millions of mobile sources across a broad geographic area.

Each source's contribution is a small percentage of the overall

problem; indeed, it is rare for emissions from even the largest single

sources to exceed 1 percent of the inventory of ozone precursors for a

single metropolitan area. Under these circumstances, even complete

elimination of any given source's emissions may well have no measurable

impact in ameliorating the nonattainment problem. Rather, attainment

requires controls on numerous sources across a broad area. Ozone is a

regional scale problem that requires regional scale reductions.

The National Academy of Sciences (NAS) study, ``Rethinking the

Ozone Problem in Urban and Regional Air Pollution'' (2) emphasized this

aspect of ozone formation. According to this report, high

concentrations of ozone occur concurrently in the Eastern United States

in urban, suburban and rural areas on scales of over 1000 kilometers.

The NAS report describes a ``persistent blanket of high ozone in the

Eastern United States'' that can last for several days. Since rural

ozone values commonly exceed 90 parts per billion (ppb) on these

occasions, an urban area needs an ozone increment of only 30 ppb to

cause an exceedance of the 1-hour ozone standard in a downwind area.

Clearly, attainment strategies must include controls on numerous

sources across broad areas.

In light of this ``collective contribution'' characteristic of

ozone formation and control, EPA proposes that if contributions from an

upwind area's emissions, taken together, are considered to be an

important portion of the downwind area's nonattainment problem, then

this factor tends to indicate that the upwind emissions as a whole, as

well as each of the upwind emitters, make a ``significant''

contribution. The fact that emissions from any particular source, or

even a group of sources, may in-and-of-themselves be small, does not

mean those sources' emissions are not ``significant'' within the

meaning of section 110(a)(2)(D). Those sources' emissions are generally

``significant'' if, when they are combined with emissions from other

sources in the same upwind area, they total upwind emissions that are

``significant.'' Even so, it should be noted that the collective

contribution factor is only one of various factors that EPA proposes to

consider in determining whether emissions from an area constitute a

``significant'' contribution to a downwind problem. The amounts of

emissions from the area and, in certain cases, emissions density,

remain important factors. Depending on all the facts and circumstances,

these other factors may tend to indicate that emissions from a

particular area should not be considered to contribute significantly,

notwithstanding the fact that those emissions may be linked in some

manner with emissions from other upwind areas that are considered to be

significant contributors.

In several rulemakings promulgated and court decisions handed down,

in the 1980's, EPA interpreted and applied the predecessors to sections

110(a)(2)(D) and 126 (e.g., State of New York v. EPA, 852 F.2d 574

(D.C. Cir. 1988); Air Pollution Control District of Jefferson County,

Kentucky v. EPA, 739 F.2d 1071 (6th Cir. 1984); Connecticut v. EPA, 696

F.2d 147 (2d Cir. 1982)). Although these rulemakings and court

decisions generally employed multifactor formulas for the ``significant

contribution'' test that bear some similarity to the formula EPA is

proposing today, they have limited relevance to the issues in the

present rulemaking because of the numerous differences in the relevant

factors. For example, in the earlier rulemakings compared to the

present rulemaking, the pollutants and precursors are different, and

the inventories of emissions and number of emitters in the upwind and

downwind areas are different. The significant contribution test is a

facts-and-circumstances analysis that depends on these factors, and

differences among these factors may yield different results under this

test. Accordingly, the differences in the key factors between the

earlier decisions and today's proposal means that those earlier

decisions are not determinative for today's proposed action.

For purposes of today's rulemaking, EPA determined the amount of

contribution to downwind air quality, under both the 1-hour NAAQS and

the 8-hour NAAQS, by employing an air quality model that assumed a zero

level of anthropogenic emissions from the various upwind areas. The

results of those model runs, as well as their other assumptions and

characteristics, are described in detail below.

As described below, EPA made separate determinations as to which

upwind areas ``contribute significantly'' to nonattainment under the 1-

hour NAAQS and under the 8-hour NAAQS. Those separate determinations

resulted in identifying the same States for both the 1-hour and the 8-

hour NAAQS.

c. Interfere with Maintenance. Section 110(a)(2)(D) also prohibits

emissions that ``interfere with maintenance'' of the NAAQS in a

downwind State. An area is obligated to maintain the NAAQS after the

area has reached attainment. This requirement of section 110(a)(2)(D)

does not, by its terms, incorporate the qualifier of ``significantly.''

Even so, EPA believes that for present purposes, the term ``interfere''

should be interpreted much the same as the term ``contribute

significantly,'' that is, through the same weight of evidence approach.

With respect to the 1-hour NAAQS, the ``interfere-with-

maintenance'' prong appears to be inapplicable. The EPA has determined

that the 1-hour NAAQS will no longer apply to an area after EPA has

determined that the area has attained that NAAQS. Under these

circumstances, emissions from an upwind area cannot interfere with

maintenance of the 1-hour NAAQS.

With respect to the 8-hour NAAQS, the ``interfere-with-

maintenance'' prong remains important. After an area has reached

attainment of the 8-hour NAAQS, that area is obligated to maintain that

NAAQS (sections 110(a)(1) and 175A). Emissions from sources in an

upwind area may interfere with that maintenance.

The EPA proposes to apply much the same approach in analyzing the

first component of the ``interfere-with-maintenance'' issue, which is

identifying the downwind areas whose maintenance of the NAAQS may

suffer interference due to upwind emissions. The EPA has analyzed the

``interfere-with-maintenance'' issue for the 8-hour NAAQS by examining

areas whose current air quality is monitored as attaining the 8-hour

NAAQS, but for which air quality modeling shows nonattainment in the

year 2007. This result is projected to occur, notwithstanding the

imposition of certain controls required under the CAA, because of

projected increases in emissions due to growth in emissions generating

activity. Under these circumstances, emissions from upwind areas may

interfere with the downwind area's ability to maintain the 8-hour

NAAQS. Ascertaining the impact on the

[[Page 60327]]

downwind area's air quality of the upwind area's emissions aids in

determining whether the upwind emissions interfere with maintenance.

d. Remedying the Significant Contribution. After identifying States

whose sources do ``contribute significantly'' to a nonattainment

problem or interfere with maintenance downwind, it is necessary to

determine the appropriate limit on emissions required in each upwind

SIP. The EPA is proposing, in the alternative, two different analyses

for the remedies which are tied to the two alternatives for the

``weight of evidence'' test.

i. Adequate Mitigation. Under the first interpretation of section

110(a)(2)(D), EPA does not consider costs in determining whether upwind

emissions contribute significantly to nonattainment or interfere with

maintenance. Instead, once EPA determines, on the basis of factors

generally related to emissions, that those emissions do contribute

significantly to nonattainment (or interfere with maintenance), EPA

then determines what emissions reductions must be required in order to

adequately mitigate these contributions. Evaluation of relative costs

enters into this determination.

Adequate mitigation would amount to eliminating a sufficient

portion of the upwind emissions so that they no longer contribute

significantly to nonattainment or interfere with maintenance.

In the present case, EPA proposes to determine an allowable level

of NOX emissions for each of the 23 jurisdictions with

sources that trigger the requirements of section 110(a)(2)(D). Given

the need to reduce this overall regional level of ozone, as discussed

earlier, EPA determined this ``budget'' of emissions by, in the first

instance, calculating the emissions achievable by applying the most

reasonable, cost-effective controls on NOX emissions in the

23 jurisdictions. The control measures considered and those determined

to be the most reasonable and cost-effective are detailed below. In

selecting those control measures determined to be the most reasonable

and cost-effective, EPA carefully considered the recommendations made

by OTAG on July 8, 1997. (The OTAG process is described in section I.F.

of this rulemaking.) The budget calculations described below generally

fall within the range of OTAG's recommendations.

The statewide emissions budgets proposed in this rulemaking were

not modeled directly to determine their air quality benefits. The EPA

believes, however, that the air quality impact of implementing these

reductions would be very similar to results previously modeled by OTAG.

This modeling is identified in section IX, Air Quality Analyses. The

downwind air quality benefits from these reductions are sufficient for

EPA to conclude that they would adequately mitigate the contribution

from the upwind sources.

ii. Elimination of Contribution. Under the second interpretation of

section 110(a)(2)(D), costs are considered as part of the calculation

as to what (if any) amount of emissions contribute significantly to

nonattainment or interfere with maintenance. The EPA proposes to

determine those amounts for each State by considering the factors

described above and the extent to which the State's emissions can be

reduced through the most cost-effective controls that reduce ozone

levels downwind. Once EPA makes this determination, EPA would conclude

that requiring those cost-effective controls is mandated under the

provisions of section 110(a)(2)(D) that require SIP provisions

``prohibiting'' that amount of emissions. Thus, under this alternative

interpretation, a SIP meets the requirement for ``prohibiting''

emissions that contribute significantly to nonattainment, or interfere

with maintenance, downwind, by implementing cost-effective controls

determined to improve air quality downwind.

iii. Comparison of the Two Legal Interpretations of Section

110(a)(2)(D). The EPA solicits comments on which of the two legal

interpretations of section 110(a)(2)(D), as described above, should be

used. Each interpretation relies on the same factors (although certain

factors enter into different parts of the analysis under the two

interpretations). Because each relies on the same factors, there is

little technical difference between the two interpretations. Each

requires the same determinations as to, for example, the ambient impact

of upwind emissions and the cost effectiveness of controls.

Moreover, as proposed in today's action, each interpretation leads

to the same conclusion as to which States are considered to have

emissions that significantly contribute to downwind problems, and as to

the amounts of NOX budgets that those States should meet.

However, the two interpretations have different legal

justifications. As noted above, section 110(a)(2)(D) provides that the

SIP for the upwind area must ``contain adequate provisions * * *

prohibiting * * * [sources] from emitting any air pollutant in amounts

which will * * * contribute significantly to nonattainment in, or

interfere with maintenance by, any other State * * *'' Under the first

interpretation, EPA may determine that a relatively larger inventory of

emissions contributes significantly to nonattainment (or interferes

with maintenance) in light of the fact that the costs of controlling

those emissions are not considered in determining significant

contribution. The EPA would then require adequate mitigation of the

full set of emissions that contribute to nonattainment or interfere

with maintenance.

Other relevant provisions indicate that the CAA could be construed

to require mitigation, and not necessarily complete elimination, of

emissions that contribute to air quality problems downwind. Section

110(k)(5) authorizes the Administrator to promulgate a SIP call

whenever she finds that a SIP is ``substantially inadequate to attain

or maintain the relevant [NAAQS], to mitigate adequately the interstate

pollutant transport described in section 176A or 184, or to otherwise

comply with any requirement of this Act'' (emphasis added). Section

176A describes interstate transport of air pollutants generally, and

section 184 describes ozone transport in the northeast region in

particular, which constitutes part of the transport phenomenon at issue

in today's proposal. Section 176A authorizes the creation of a

transport region when emissions from one or more States contribute

significantly to a NAAQS violation in another State and further

authorizes a transport commission to, among other things, assess

strategies for mitigating the interstate pollution. These provisions,

read together, indicate that adequate mitigation of transport is an

appropriate response to a SIP call. Arguably, this interpretation

should hold when EPA issues a SIP call based on section 110(a)(2)(D),

and when EPA mandates a SIP revision under section 110(a)(1), based on

section 110(a)(2)(D).

The second interpretation focuses on the provisions of section

110(a)(2)(D) that the SIP must include provisions to ``prohibit'' any

emitting activity from emitting in ``amounts'' that contribute

significantly to downwind nonattainment or interfere with maintenance.

The EPA has determined the States whose full set of NOX

emissions contribute markedly to downwind problems. The term

``prohibit'' could be interpreted to require EPA, upon finding that a

State's full set of emissions ``contribute significantly'' to

nonattainment, must then require the SIP to eliminate that full set of

emissions. This construction

[[Page 60328]]

could mean that EPA must require the State to shut down all of the

emission-generating activities. It is doubtful Congress would have

intended this result.

The EPA's second interpretation avoids this possible result by

taking into account the relative cost effectiveness of the upwind and

downwind controls in defining the ``amounts'' of emissions in each

State that contribute significantly to the downwind problem. Once EPA

has set those ``amounts'' in light of its consideration of the cost

factors, the SIPs for the affected States would then need to prohibit

only those amounts.

iv. Other Issues. States will have the flexibility to choose their

own mix of control measures to meet the proposed statewide emissions

budgets. That is, States are not constrained to adopt measures that

mirror the measures EPA used in calculating the budgets. In fact, EPA

believes that many control measures not on the list relied upon to

develop EPA's proposed budgets are reasonable--especially those like

enhanced vehicle inspection and maintenance programs that yield both

NOX and VOC emissions reductions. Thus, one State may choose

to primarily achieve emissions reductions from stationary sources while

another State may focus emission reductions from the mobile source

sector. Furthermore, States may choose to pursue cost-effective energy

efficiency opportunities as a means to reduce the control measures

necessary to meet their statewide emission budgets.

e. Control Implementation and Budget Attainment Dates. The EPA

proposes to require that the SIP revisions impose an implementation

date for the required controls of 3 years from the date of the required

SIP submission, which would result in compliance by those sources by no

later than September 2002. However, the EPA is soliciting comments on

the range of implementation dates from between September 2002 and

September 2004. The EPA seeks comment on which date within this 2-year

range is appropriate, in light of the feasibility of implementing

controls and the need to provide air quality benefits as expeditiously

as practicable. The EPA is proposing an implementation date of

September 2002 in order to allow coordination of this rulemaking with

its response to 8 section 126 petitions which are discussed below in

section I.E, Section 126 Petitions. Although the EPA's actual proposed

compliance date is September 2002, because the Agency is seeking

comment on a range from September 2002 to September 2004, the Agency

refers to the range of implementation dates throughout this rulemaking.

The EPA further proposes that States be required to meet the mandated

budgets by the end of the year 2007, by which time additional

reductions from various Federal measures will also be achieved.

The EPA believes that requiring implementation of the upwind

controls, and thereby mandating upwind reductions, by no later than

these 2002-4 dates, is consistent with the attainment schedule for the

downwind areas. Because the downwind areas depend on upwind reductions

to reach attainment, mandating upwind controls on a schedule consistent

with downwind attainment requirements is appropriate.

A review of the attainment schedule under the 1-hour NAAQS would be

useful. Under the attainment schedule, serious areas are required to

attain by the end of 1999, severe-15 areas are required to attain by

the end of 2005, and severe-17 areas are required to attain by the end

of 2007 (section 181(a)(1)). If a serious area fails to meet its 1999

attainment date, it is to be reclassified (``bumped up'') to severe-15

(section 181(b)(2)). However, an area may fail to reach attainment by

its attainment date, but avoid bump up, if EPA grants a 1-year

extension. An area is eligible for a 1-year extension if, among other

things, it has no more than one exceedance of the NAAQS in the

attainment-date year. The EPA may grant another extension for the next

year under the same conditions (section 181(a)(5)). If an area receives

two 1-year extensions, it may reach attainment in the following year

(the second year after the attainment-date year) if, again, it has no

more than one exceedance of the NAAQS. Under these circumstances, the

area will have had no more than three exceedances over a 3-year period

(the attainment-date year and the 2 next years), which would qualify it

for attainment under the 1-hour NAAQS. The EPA has indicated that once

it determines that an area has achieved air quality that satisfies the

1-hour NAAQS, the NAAQS will be rescinded with respect to that area.

Although controls on upwind emissions are designed to assist

downwind nonattainment areas in reaching the NAAQS, EPA is aware that

at this point, it is not possible for EPA to mandate controls on upwind

areas within the OTAG region in sufficient time to help serious areas

reach attainment by their end-of-1999 attainment date. The amount of

time that is necessary to assure that the rulemaking proposed today is

well considered by all affected parties, added to the amount of time

necessary for the States to adopt the required SIP revisions, and the

amount of lead-time necessary to implement the required controls, means

that those controls cannot be expected to be in place in time to assist

the serious areas in reaching their attainment date.

The next attainment date is 2005, which applies to severe-15 areas,

such as the Baltimore area, and which would apply to any serious area

that is bumped up. The EPA's proposal to require upwind controls to be

implemented by no later than September 2004--in time for the beginning

of the ozone season for the affected States--is sensible in light of

this 2005 attainment date. Implementing controls earlier than September

2004, or at least phasing in some controls, if not all of them, prior

to that date, would improve the chance for minimizing exceedances

during the 3-year period up to, and including, 2005, which will

facilitate reaching attainment as of this date. In particular, to the

extent that the State chooses controls on major stationary sources of

NOx, EPA believes it would be feasible to implement some of those

controls earlier than September 2004. However, EPA is aware that

implementation of controls for other sources may be more problematic.

The EPA solicits comments on what dates within the range of 3 to 5

years of the required SIP submission would be appropriate for

implementation of the controls.

Full implementation by no later than September 2004 would mean that

all of the upwind controls required under the rulemaking proposed today

would be in place as of the November 15, 2005 attainment date for the

downwind severe-15 areas. Failure to implement those controls prior to

September 2004 may mean that the downwind area may record too many

exceedances in the 3-year period prior to the end of 2005, so that it

would not be possible to reach attainment as of that time. However,

implementation of these reductions by September 2004, coupled with any

necessary additional reductions from the downwind sources, may result

in no more than one exceedance in the downwind area during the

attainment year and during each of the next 2 years thereafter. Under

these circumstances, the downwind area would be eligible for the 1-year

extensions described above and would reach attainment by the year 2007.

Similarly, full implementation by September 2004 would mean that

severe-17 areas would receive the benefit of reduced upwind emissions

during the 3-year period up to, and including, their 2007 attainment

year. In the OTAG region, the severe-17 areas

[[Page 60329]]

include the Philadelphia, New York, Milwaukee, and Chicago areas. These

reductions should greatly assist the downwind areas in reaching

attainment by the end of 2007.

An implementation date of between September 2002 September 2004 is

also consistent with the attainment date scheme for the 8-hour NAAQS.

The EPA intends to promulgate designations for areas under the 8-hour

NAAQS by the year 2000. The CAA provides for attainment dates of up to

5 years or 10 years after designation. Therefore, the first attainment

date for many areas under the 8-hour standard could be 2005. Section

172(a)(2)(C) has a two, 1-year extension scheme applicable for areas

under the 8-hour NAAQS that is similar to that described above, under

section 181(a)(5), applicable to areas under the 1-hour NAAQS.

Accordingly, full implementation of mandated SIP controls in the upwind

areas by no later than September 2004 may allow downwind areas to reach

attainment of the 8-hour NAAQS by 2007, counting the two 1-year

extensions in the same manner as for severe-15 areas under the 1-hour

NAAQS. In addition, the EPA believes that compliance no later than

September 2004 by the utility and nonutility sector, with the emission

limits assumed in setting the emission budgets or application of

controls to other source categories, is feasible.

Further, EPA notes that the September 27, 1994 OTC NOX

Memorandum of Understanding (MOU) provides that large utility and

nonutility NOx sources should comply with the Phase III controls by the

year 2003. The levels of control in the MOU are 75 percent or 0.15 lb/

106 btu in the inner and outer zones, levels comparable to

the controls assumed in setting the budget for this rulemaking. In

addition, in comments to EPA's proposed Phase II NOx reduction program

under the Acid Rain provisions of the CAA 3, the Institute

of Clean Air Companies (ICAC) stated that more than sufficient vendor

capacity existed to supply retrofit of selective catalytic control to

the boilers affected by the proposed rule. The ICAC in fact indicated

that additional catalyst capacity could be added if needed.

---------------------------------------------------------------------------

\3\ Letter of January 29, 1997 from Jeffrey C. Smith, Executive

Director, Institute of Clean Air Companies, to Docket No. A-95-28:

Acid Rain Program, Nitrogen Oxides Emission Reduction.

---------------------------------------------------------------------------

Although EPA is proposing today that SIPs mandate implementation of

the required SIP controls by a date within a range of September 2002

and September 2004, EPA is also proposing that the affected States

demonstrate achievement of their NOX budgets as of the end

of the year 2007. In addition, EPA used the 2007 date to analyze for

modeling purposes the impact of upwind emissions on nonattainment air

quality. Using the 2007 date means that the States will be able to

account for the additional reductions from Federal measures occurring

between the date that SIP controls are implemented and the end of 2007,

although the State must also account for growth in emissions during

this time. Using the 2007 date is sensible in part because OTAG used

this date for these purposes and compiled substantial technical

information--such as information concerning inventories--based on this

date. It is, therefore, efficient for EPA to use this same information.

Developing comparable information for an earlier date would be time

consuming and resource intensive. In addition, it is uncertain that

there would be significant differences in amounts of emissions and

impact on ambient air quality between an earlier date and 2007, in

light of the fact that during this period, emissions would generally

increase somewhat as a result of growth in activities that generate

emissions, but would also decrease due to continued application of

federally mandated controls. Accordingly, requiring accounting for a

budget as of the 2007 date is both practicably indicated and is a

reasonable surrogate for requiring this accounting as of September

2004.

E. Section 126 Petitions

The EPA has received section 126 petitions from eight States:

Connecticut, Maine, Massachusetts, New Hampshire, New York,

Pennsylvania, Rhode Island and Vermont. The petitions vary as to the

type and geographic location of sources they identify as meriting a

finding of significant contribution. The petitions also vary as to the

levels of controls they recommend. In addition, EPA has received a

petition from the State of Wisconsin asking EPA to promulgate a SIP

call under section 110(k)(5) requiring the States of Illinois, Indiana,

Iowa, Kentucky and Missouri to submit SIP revisions addressing the

purported impact of their emissions on Wisconsin. By letter dated

August 8, 1997, from Mary D. Nichols, Assistant Administrator for Air

and Radiation, to Michael J. Walls, Chief, Environmental Protection

Bureau, Office of the Attorney General, State of New Hampshire, EPA

provided technical guidance concerning section 126 petitions. The EPA

is now studying the petitions and will prepare a notice(s) of proposed

rulemaking to grant or deny them.

The EPA's response to a section 126 petition differs from today's

action in several ways. Today's action is a proposed SIP call under

section 110(k)(5) for SIP provisions meeting the requirements of

section 110(a)(2)(D) for the 1-hour ozone NAAQS, coupled with a

proposed requirement under section 110(a)(1) for submission of SIP

provisions meeting the requirements of section 110(a)(2)(D) for the 8-

hour ozone NAAQS. The EPA bases this action on a technical analysis as

to whether the entire NOX emissions inventory of an

individual upwind State contributes significantly to an ozone

nonattainment problem downwind. If EPA concludes that the

NOX emissions from that State make such a significant

contribution, EPA will require the State to submit SIP provisions that

limit the State's NOX emissions to the level mandated by

EPA, but through any combination of measures affecting any sector of

the inventory chosen by the State. If the State does not make the

required submission, EPA may, among other things, promulgate a FIP in

accordance with section 110(c).

By comparison, a section 126 petition, by the terms of section

126(b)-(c), is limited to upwind major stationary sources and not other

sectors of the upwind emissions inventory. Moreover, a section 126

petition may seek a finding concerning upwind sources in more than one

State. Further, if EPA grants the petition, it is EPA, and not the

States, that promulgates direct controls for the major sources.

The EPA's response to section 126 petitions would bear relevance to

today's action. The section 126 petitions and section 110(k)(5)/

110(a)(1) action both require technical analysis of whether upwind

sources contribute significantly to a downwind nonattainment or

maintenance problem. However, EPA's section 110(k)(5)/110(a)(1) action

results in a mandate for the States to submit SIP revisions that

conform to only minimum guidance provided by EPA. On the other hand,

the section 126 petitions, if granted, would result in EPA selection

and imposition of controls directly on major stationary sources. These

controls could provide a template for the SIP provisions the States

must include in their rulemaking response to EPA's section 110(k)(5)/

110(a)(1) rulemaking or, if necessary, a FIP.

EPA believes that both the 110 process as outlined and 126 petition

processes are aimed at addressing regional transport of ozone forming

pollutants and can be fully coordinated. The 110 process outlined

provides the potential to deal comprehensively with

[[Page 60330]]

transported pollutants that contribute significantly to downwind

nonattainment, and importantly, allows individual States to make

choices about cost-effective source controls best fitting their unique

State situations. The 126 petition process provides assurance to

petitioning States that upwind sources of air pollution will be

addressed in a timely manner. Thus, each of these processes may provide

important and complementary tools to address the regional ozone

transport problem.

Over the next several months, EPA will be working with the affected

States to ensure these two processes are fully coordinated. This will

provide maximum certainty for State and business planning requirements.

The EPA's goal in this effort will be to ensure that States achieve the

air quality reductions EPA determines through rulemaking are necessary

to address regional transport while providing the maximum flexibility

to those States in identifying the appropriate means to meet those

goals.

F. OTAG Process

The OTAG has completed the most comprehensive analysis of ozone

transport ever conducted. The process has resulted in more technical

information being gathered and more modeling and monitoring analyses on

regional ozone transport than ever before. The OTAG process was

fundamentally different from previous efforts undertaken by the Federal

Government and the States to assess and solve air pollution problems.

What was unique about the multistate, multistakeholder OTAG process is

that for the first time, the Federal Government has looked to the

States involved to provide the necessary technical information and to

aid in determining an outcome which has local, regional and national

implications.

The OTAG was organized into a number of subgroups and work groups

that included members from the States, EPA, industry and environmental

groups. The OTAG's Policy Group, comprised of the State Environmental

Commissioners, provided overall direction to its subgroups for the

assessment of ozone formation and transport, as well as the development

of control strategies that will reduce concentrations of ozone and its

precursors. The subgroups within OTAG addressed issues relating to

emissions inventories, monitoring, modeling, and evaluated the

availability, effectiveness, and costs of potential national, regional

and local air pollution control strategies. Specific issues such as

trading and market-based incentives were also addressed.

The OTAG's initial meetings were on May 18, 1995, in Reston, VA,

and June 19, 1995, in Washington, DC. The OTAG continued to meet

regularly for 2 years until their final meeting in Washington, DC on

June 19, 1997. The goal of OTAG was to:

* * * identify and recommend a strategy to reduce transported ozone

and its precursors which, in combination with other measures, will

enable attainment and maintenance of the national ambient ozone

standard in the OTAG region. A number of criteria will be used to

select the strategy including, but not limited to, cost

effectiveness, feasibility, and impacts on ozone levels. (1)

To meet its goal, OTAG used technical information from air quality

analyses and photochemical modeling. The OTAG modeled three rounds of

emission reduction scenarios and strategies, including varying control

measures geographically. The first round of modeling was performed

during September and October 1996 and provided an initial evaluation of

possible OTAG emission reduction scenarios. The second round was

performed during November and December 1996 and refined the emission

reduction level for the strategies. The third round was performed

during January through March 1997 and evaluated the geographic

applicability of the OTAG strategies. These geographic modeling runs

provided information on applying different levels of controls on

utilities and nonutility point sources at incremental steps. Round-3

also included a limited number of additional modeling runs needed to

address comments made by a number of States related to the geographical

boundaries of the zones defined for round-3 modeling. The OTAG modeling

results are discussed in section II, Weight of Evidence Determination

of Significant Contribution, and are also available on the OTAG

webpage. This modeling, along with other OTAG-generated information,

provided the technical information necessary to make recommendations to

the Policy Group and to EPA on what is needed to meet the OTAG goal.

The EPA received OTAG's final recommendations on July 8, 1997. These

recommendations are included in Appendix B.

II. Weight of Evidence Determination of Significant Contribution

A. Introduction

This section documents the technical information and analyses for

the factors concerning emissions and contributions to ambient air

quality that EPA uses to determine which States in the OTAG domain make

a significant contribution to nonattainment in downwind

States.4 To a large extent, this assessment is based upon

the results of OTAG modeling and air quality analyses as well as

information from other non-OTAG modeling studies. The OTAG modeling

available for this analysis includes a set of initial emissions

sensitivity runs, the regional strategy runs in rounds 1, 2, and 3, and

the geographic sensitivity runs performed to support the design of

strategies in round-3.

---------------------------------------------------------------------------

\4\ Under the two alternative interpretations of section

110(a)(2)(D) that EPA is proposing today, if upwind emissions meet

the factors related to emissions and contribution to ambient air

quality, EPA would conclude either that the emissions significantly

contribute to a nonattainment problem, or the emissions may

significantly contribute, depending on further analysis of other

factors, including costs.

---------------------------------------------------------------------------

B. Background Technical Information

The importance of interstate transport to the regional ozone

problem and contributions from upwind States to downwind States is

supported by numerous studies of air quality measurements and modeling

analyses. In general, ozone episodes can occur on many spatial and

temporal scales ranging from localized subregional events lasting a day

or 2, up to regionwide episodes lasting as long as 10-14 days. The

frequency of localized versus regional episodes depends on the

characteristics of the large-scale meteorological patterns which

control the weather in a particular summer season. Local controls alone

are not sufficient to reduce ozone during regionwide episodes since a

substantial amount of ozone may be transported into the area from

upwind sources. The National Research Council report, ``Rethinking the

Ozone Problem in Urban and Regional Air Pollution'', (2) cites numerous

studies of widespread ozone episodes during summertime meteorological

conditions in the East. These episodes typically occur when a large,

slow-moving, high pressure system envelopes all, or a large portion of,

the Eastern United States. The relatively clear skies normally

associated with such weather systems favor high temperatures and strong

sunlight, which enhances the formation of high ozone concentrations. In

addition, the wind flow patterns can lead to a build up of ozone

concentrations and the potential for long-range ozone transport.

Specifically, winds are generally light in the center of high pressure

systems so that areas

[[Page 60331]]

under the center may have near-stagnation conditions resulting in the

formation of high ozone levels. As the high pressure system moves

eastward, winds become stronger on the ``backside'' which increases the

potential for these high ozone levels to be transported to more distant

downwind locations. Over several days, the emissions from numerous

small, medium and large cities, major stationary sources in rural

areas, as well as natural sources, combine to form a ``background'' of

moderate ozone levels ranging from 80 to 100 ppb (2) of which 30 to 40

ppb may be due to natural sources. Concentration levels in the range of

80 to 100 ppb and higher have also been measured by aircraft aloft,

upwind of the Lake Michigan area (3), as well as the Northeast Corridor

(4). Because this level of background ozone is so close to the NAAQS,

even a small amount of locally-generated ozone will result in an

exceedance.

The importance of the episodic meteorological conditions is

heightened by the spatial distribution of emissions across the region.

The EPA has examined the State total emissions and emissions density

projected by OTAG to 2007, as described in section B.2, OTAG Strategy

Modeling. Both of these measures of emissions (i.e., total and density)

are important considerations for ozone formation. Total emissions

indicate the amount of mass emitted by a State while emissions density

indicates the degree to which those emissions are concentrated within

the State and provides a way to compare emissions between

geographically large and small States on a more equivalent basis. The

State total emissions in Table II-1 indicate that there is no single

State or group of adjacent States that stand out as the major

contributors to the total manmade emissions in the OTAG region. Rather,

many States in the Midwest, Northeast and Southeast have high levels of

emissions. For example, Illinois, Indiana, Ohio, Kentucky, Michigan,

Pennsylvania, New York, Alabama, Georgia, Florida, North Carolina and

Tennessee each have total NOX emissions exceeding 1000 tons

per day. Even some other smaller States like Connecticut, Delaware,

Maryland, Massachusetts, and Rhode Island, along with the District of

Columbia, have a high spatial density of NOX emissions as

indicated in Table II-2. Thus, considering the distribution of

emissions, a broad range of emissions from many States contribute to

the regional background ozone during episodic meteorological

conditions. In this situation, there is a cumulative effect in that the

thousands of stationary sources and millions of motor vehicles

throughout the OTAG region collectively cause downwind contributions as

they generate emissions and those emissions interact over multiple

days.

1. OTAG Modeling Process

As described in the OTAG Modeling Protocol (5), state-of-the-

science models and data bases were used in OTAG for simulating the

physical and chemical processes involved in the formation and transport

of ozone and precursor species over multiday episodes and regional

scales. As such, the OTAG modeling system provides the most complete,

scientifically-credible tools and data available for the assessment of

interstate transport. All of the OTAG model runs were made for an area

covering a large portion of the Eastern United States, as shown in

Figure II-1. This area includes all or portions of 37 States, the

District of Columbia and southern Canada. In general, the OTAG

``modeling domain'' (i.e., OTAG region) was set large enough to

encompass the widespread spatial extent of high ozone levels measured

during multiday episodes in the eastern half of the United States. As

such, the domain is designed to handle the synoptic (i.e., large) scale

meteorological conditions associated with regional transport and to

include the major emissions source areas in the East. The horizontal

grid configuration used by OTAG (see Figure II-1) includes a ``Fine

Grid'' at 12 km resolution ``nested'' within a ``Coarse Grid'' at 36 km

resolution. The size and location of the ``Fine Grid'' was determined

based on the location of areas with high ozone concentrations, the

geographic variations in emissions density, the meaningful resolution

of some model inputs, computer hardware limitations, and model run

times. As described in section B.3, OTAG Geographic Modeling, OTAG

applied different levels of controls in the ``Fine Grid'' versus the

``Coarse Grid'' as part of the round-3 modeling.

Four specific episodes were selected by OTAG for model simulations

in order to provide information on a range of meteorological conditions

which occur during periods of elevated ozone levels. These episodes

are: July 1-11, 1988; July 13-21, 1991; July 20-30, 1993 and July 7-18,

1995. Each of these episodes represents somewhat different episodic

characteristics in terms of transport patterns and the spatial extent

of high ozone concentrations in the East (6). The 1988 and 1995

episodes featured high ozone concentrations in the Northeast, Midwest,

and Southeast with wind regimes that provided the meteorological

potential for intra- and inter-regional transport. During the 1991

episode, high ozone was confined mainly to the northern portion of the

OTAG domain, whereas the 1993 episode was a ``Southeast'' episode with

relatively low ozone levels outside this region. It should be noted

that none of the OTAG episodes include extensive periods of high ozone

in the far western portions of the domain nor in areas along the gulf

coast.

As part of OTAG, an objective evaluation of model predictions was

conducted for each of these four episodes in order to determine the

performance of the modeling system for representing regional ozone

concentration levels. This evaluation focused on a number of

statistical metrics comparing predicted ozone to ground-level ozone

measurements (7). The results indicate generally good agreement between

simulated and observed values. Most importantly, areas of predicted

high ozone correspond to areas of observed high ozone. However, a few

relatively minor concerns were found, such as:

A tendency to underestimate concentrations in the North

and overestimate concentrations in the South;

Concentrations at night are somewhat underestimated

relative to daytime predictions;

Low observed concentrations tend to be overestimated and

higher observed values tend to be underestimated; and

Concentrations at the start of the episode tend to be

underestimated with a tendency for concentrations at the end of the

episode to be overestimated.

The success of the model for predicting pollutant concentrations

aloft is also important from a transport perspective. During the day,

when the atmosphere is ``well mixed,'' ground-level ozone values can

serve as a good measure of both local formation and transport. However,

at night, ozone is depleted in a very shallow layer near the ground due

to deposition and nighttime chemical reactions. Thus, during the

overnight and early morning, ground-level measurements and predictions

do not adequately reflect pollutant transport. Aircraft-measured

pollutant data and model predictions during these periods indicate

moderate to high levels of ozone aloft which can then mix down during

the day and further elevate ground-level concentrations. A limited

amount of measured data aloft are available from non-OTAG field studies

for several of the days in the 1991 and 1995 episodes. An initial

comparison of these data to

[[Page 60332]]

the model predictions (6) indicates that model performance aloft is not

as good as for ground-level ozone. In general, the model tends to

underestimate ozone aloft. This suggests that the model may somewhat

underestimate the amount of ozone transport aloft, especially overnight

into the early morning hours. Thus, the contribution of upwind source

regions to ozone levels in downwind areas may actually be greater than

estimated by the model.

2. OTAG Strategy Modeling

The OTAG strategy modeling was conducted in several phases. In each

phase, the effects on ozone 5 of various changes in

emissions were examined relative to a future-year baseline. This

baseline reflects the projection of emissions from 1990 to 2007.

Included in the 2007 baseline are the net effects of growth and

specific control programs prescribed in the 1990 Amendments. The

control measures included in the 2007 baseline are listed in Table II-

3. Overall, domainwide emissions of NOX in the 2007 baseline

are approximately 12 percent lower than 1990 while emissions of VOC are

approximately 20 percent lower. The procedures for developing the 1990

base inventory and the 2007 baseline are described by Pechan (8). The

key findings (6) from comparing the model predictions for the 2007

baseline to the 1990 base case scenario are:

---------------------------------------------------------------------------

\5\ Although the OTAG assessments focussed on 1-hour

concentrations, the impacts on 8-hr average concentrations were

found to be similar to these for 1-hour values.

---------------------------------------------------------------------------

Ozone levels are generally reduced across most of the

region, including nonattainment areas;

Some increases in ozone are predicted in areas where

higher economic growth is expected to occur, especially in the South;

Ozone levels aloft along regional ``boundaries'' are

reduced, but average concentrations above 100 ppb and peak

concentrations above 120 ppb are still predicted on several days; and

Ozone concentrations above the 1-hr and/or 8-hr NAAQS may

still occur in the future under similar meteorological conditions in

many of the counties currently violating either or both of these NAAQS.

The 2007 baseline emissions were reduced in an initial set of

sensitivity modeling performed to assess several broad strategy-

relevant issues. All of these model runs involved ``across-the-board''

emissions reductions (i.e., no source category-specific reductions).

The results (6) of these simulations are as follows:

Regional reductions in NOX emissions decrease

ozone across broad portions of the region including ozone in areas

violating the NAAQS;

Regional reductions in VOC emissions decrease ozone in and

near the core portions of urban areas with relatively small regional

benefits;

Both elevated and low-level NOX reductions

decrease ozone concentrations;

NOX reductions can produce localized, transient

increases in ozone (mostly due to low-level, urban NOX

reductions) in some areas on some days; most increases occur on days

and in areas where ozone is low (i.e., below the NAAQS);

NOX plus VOC reductions lessen ozone increases

in urban areas, but provide little additional regional benefits

compared to NOX-only reductions; and

The magnitude and spatial extent of changes in 8-hour

ozone concentrations are consistent with the changes predicted in 1-

hour concentrations.

Based upon the findings of the sensitivity runs, OTAG subsequently

developed and simulated source-specific regionwide control strategies

in two rounds of modeling. These strategies were derived from a range

of control measures applied to individual source categories of VOC and

NOX (8). The controls were grouped into various levels of

relative ``stringency'' as listed in Tables II-4a and II-4b. The round-

1 and round-2 modeling consisted of strategies that contained various

combinations of controls from the least (level ``0'') to most stringent

(level ``3'') for each source category. The control levels and

domainwide emissions associated with these strategies are given in

Tables II-5a and II-5b.

The round-1 modeling was a ``bounding analysis'' with runs that

ranged from the lowest level of control on all source categories (Run

1) to the highest level of control on all sources (Run 2). Runs 3 and

4b were included to isolate the effects of the most stringent OTAG

controls on utilities only, versus this level of control on the other

source categories. In the round-2 modeling, eight runs were simulated

to examine the relative benefits of progressively increasing the level

of control on utilities, under two alternative levels of control

applied to area, nonroad and mobile sources. The results (6) of the

round-1 and round-2 modeling are given in Table II-6.

The findings from the round-1 and round-2 OTAG strategy modeling

which are particularly relevant to this analysis are:

Clean Air Act programs will likely provide a reduction in

ozone concentrations in many nonattainment areas; however, some areas

currently in nonattainment will likely remain nonattainment in the

future and new 8-hr nonattainment and/or maintenance problem areas may

develop as a result of economic growth in some areas;

NOX reductions from elevated and low-level

sources are both beneficial when considered on a regional basis; and

Further mitigation of the ozone problem will require

regional NOX-oriented control strategies in addition to

local VOC and/or NOX controls necessary for attainment in

individual areas.

3. OTAG Geographic Modeling

In the round-1 and round-2 strategy modeling, controls were applied

across the entire domain. In round-3, controls were applied on a

geographic basis in order to assess the relative effects of different

strategies in various portions of the region. Prior to developing these

strategies, a series of sensitivity tests was conducted by OTAG to

provide information on the spatial scales of transport in order to help

determine where to apply various levels of control. The most relevant

tests are the ``subregional'' modeling and the ``rollout'' modeling.

The base case for these tests was the 2007 baseline scenario. In the

subregional modeling, the domain was divided into the 12 subregions

shown in Figure II-2. For one set of subregional modeling, all

anthropogenic emissions were eliminated from each subregion,

individually in separate model runs. These runs, called the ``zero-

out'' subregional scenarios, were performed for the 1988 and 1995

episodes. In a second set of subregional modeling, emissions were

reduced, but not eliminated in each subregion. The level of reductions

were 60 percent for elevated point-source NOX emissions, 30

percent from all other sources of NOX, and 30 percent from

all sources of VOC. These runs are referred to as the ``5c''

subregional scenarios. The ``5c'' scenarios were run for most, but not

all, subregions for the 1988, 1991 and 1995 episodes. In addition to

looking at individual subregions, there were runs for 1988 and 1991

which applied the ``5c'' reductions in subregions 5, 6, and 9 (Figure

II-2) combined in order to determine the relative impacts of expanding

the size of the area of emissions reductions.

In the rollout modeling, the ``5c'' emissions reductions were

applied first within selected areas and, then, outward

[[Page 60333]]

in incremental steps (rollouts) of approximately 200 km from these

areas, in subsequent runs. Three major nonattainment areas in the

region (Atlanta, the Lake Michigan Area, and New York City) were

selected by OTAG for this type of modeling.

The results (6) of the OTAG geographic modeling indicate the

following:

Emissions reductions in a given multistate region/

subregion have the most effect on ozone in that same region/subregion;

Emission reductions in a given multistate region/subregion

also affect ozone in downwind multistate regions/subregions;

Downwind ozone benefits decrease with distance from the

source region/subregion (i.e., farther away, less effect);

Downwind ozone benefits increase as the size of the upwind

area being controlled increases, indicating that there is a cumulative

benefit to extending controls over a larger area; and

Downwind ozone benefits increase as upwind emission

reductions increase (the larger the upwind reduction, the greater the

downwind benefits).

The round-3 strategies were based in large part on the results of

the geographical sensitivity runs. The cornerstone of round-3 was a set

of geographic ``zones'' (see Figure II-3) which was used to vary the

level of control across the OTAG region. For the most part, OTAG

focussed the round-3 controls on zones in the ``Fine Grid.'' This was

based upon an analysis indicating that, in general, the greatest

potential for regional transport leading to inter-state impacts of

concern occurs within the ``Fine Grid'' portion of the OTAG region. The

individual zones were used to differentiate the impacts of controls in

and close to the three major 1-hour nonattainment areas of the ``Fine

Grid'' (i.e., the Northeast Corridor, Atlanta, and Chicago/Milwaukee)

versus controls in zones farther upwind of these areas. Specifically,

in round-3 various levels of utility and nonutility controls were

applied by zone in different runs. The level of control for each

strategy is given in Table II-7. In general (except for Run F), the

round-3 runs progressively increase the level and spatial extent of

utility and nonutility controls starting with the reference run (Run A)

through the most stringent run (Run I). In addition, there were a

number of supplemental round-3 runs (6) performed using a modified

version of the zones. The most relevant of these were Runs CA and CB

which altered the configuration of zones II, III, and IV to correspond

more closely to the borders of the OTR.

The results (6) of the OTAG round-3 runs indicate the following:

The greater the emissions reductions the greater the ozone

benefits (Run I was the most effective strategy and Run A the least);

There was no bright-line between the incremental

application of controls nor any leveling off of benefits with the more

stringent controls;

Increasing the spatial extent of emissions reductions

increases the amount and spatial extent of ozone benefits downwind;

areas farther upwind may need a higher level of control to have a given

effect in a particular downwind area;

In general, emissions reductions in a given zone have the

greatest effects within that zone; but there are also impacts on high

ozone concentrations in other zones downwind;

Emissions reductions in zones I, III, and V are

``effective and necessary'' (6) to reduce ozone in the Lake Michigan

area, the Northeast Corridor, and Atlanta, respectively which are the

closest downwind areas to each of these zones;

Emissions reductions in more distant zones also help

reduce ozone in these three major nonattainment areas; emissions

reductions in zone II benefit the Northeast Corridor and the Lake

Michigan area; emissions reductions in zone IV benefit Atlanta and the

Lake Michigan area;

Emissions reductions in zones II and IV are also

``effective and necessary'' (6) to reduce ozone in ``problem areas''

within these zones (e.g., Birmingham, Nashville, Charlotte, Richmond,

Louisville, and Cincinnati);

When viewed on a regional basis, it may be ``difficult to

geographically distinguish between control levels'' (6) because there

are ozone problem areas in every zone within the ``Fine Grid'' and

there are clearly interzonal impacts;

Additional emissions reductions in ``Coarse Grid'' States

``are not very effective'' (6) in reducing high ozone levels downwind

in problem areas of the ``Fine Grid''; and

Although the OTAG assessments focused on 1-hour

concentrations, the impacts on 8-hour average concentrations were found

to be similar to those for 1-hour peak values, suggesting that ``a

regional strategy designed to help meet'' the 1-hour NAAQS ``will also

help meet'' the 8-hour NAAQS (6).

Overall, the findings from the OTAG sensitivity and strategy

modeling indicate that:

Areas of high ozone, both measured and predicted for the

future, occur, or will occur, in most portions of the modeling domain;

Several different scales of transport (i.e., inter-city,

intra-state, inter-state, and inter-regional) are important to the

formation of high ozone in many areas of the East;

The greatest potential for inter-state and inter-regional

impacts associated with transport occurs between States within the

multistate ``Fine Grid'' area;

A regional strategy focussing on NOX reductions

across a broad portion of the region will help mitigate the ozone

problem in many areas of the East;

There are ozone benefits across the range of controls

considered by OTAG; the greatest benefits occur with the most emissions

reductions; there was no ``bright line'' beyond which the benefits of

emissions reductions diminish significantly;

Even with the large ozone reductions that would occur if

the most stringent controls considered by OTAG were implemented, there

may still remain high concentrations in some portions of the OTAG

region;

A regional NOX emissions reduction strategy

coupled with local NOX and/or VOC reductions may be needed

to enable attainment and maintenance of the NAAQS in this region.

It should be noted that urban-scale analyses will be necessary in

order for States to develop local attainment plans. These analyses will

take into account more geographically refined emissions and local

meteorological factors, such as lake and sea breezes and/or topography.

Urban-scale modeling is also necessary to more precisely evaluate the

degree and extent of any NOX disbenefit.

4. Other Relevant Analyses

In addition to the OTAG modeling described above, the potential for

regional ozone transport has been examined by the OTAG Air Quality

Assessment Work Group using trajectory analyses, wind vector

characterization, and statistical analyses of ozone measurements. The

trajectory analyses (9) were used to identify a ``distance scale''

indicative of the 1- to 2-day transport distance of ozone and

precursors. The results suggest that ozone-laden air may travel

distances of 150 miles to 500 miles or more into and across the Midwest

and Northeast. Analyses, as part of the Southern Oxidants Study (10),

indicate that most southern episodes may be more closely linked to

near-stagnation conditions and thus, shorter transport distances might

[[Page 60334]]

be expected within the Southeast. Additional information on regional

transport patterns comes from an analysis conducted by OTAG to

characterize the regional wind flow patterns typically associated with

high ozone in the Northeast, Southeast, and Midwest (9). These wind

vectors (Figure II-4) indicate that regional episodes are typically

associated with broad-scale anticyclonic (i.e., clockwise) flow regimes

centered over the Ohio-Tennessee Valley area. Under these conditions,

there are typically lighter winds and weaker transport within the South

compared to other regions. However, the information also indicates the

potential for transport from the South to other portions of the region.

For example, in the Midwest, high ozone is generally associated with

wind flows from States located to the south and southwest. For the

Northeast, the data suggest a strong westerly flow favoring transport

from States farther to the west.

Another method for estimating the potential range of transport was

developed by Rao (11) based on correlating daily ambient ozone

measurements between monitoring sites for the period 1985 through 1994

for several nonattainment areas (i.e., Atlanta, Washington DC,

Cincinnati, Pittsburgh and Chicago). The analysis indicates the

presence of ``ozone clouds'' surrounding these areas which are likely

the result of pollutant transport, spatial patterns in emissions, and

weather conditions conducive to ozone formation. The spatial extent of

these ``ozone clouds'' is on the order of 300 miles or more, extending

from the central portion of the nonattainment area along the axis of

the major transport direction.

The importance of mitigating transported ozone for solving the

nonattainment problem for many cities in the East has been examined as

part of ongoing urban scale modeling analyses by various State

agencies. In urban scale modeling, transport into the nonattainment

area is represented by specifying pollutant concentrations along the

sides and top of the modeling domain. These ``boundary condition''

concentrations reflect ozone transport into the urban area at the

surface and aloft. As such, incoming ozone (as well as precursor

chemical species) moves into the urban area and mixes with local

emissions to increase the formation of ozone. The available urban scale

modeling work is summarized in a report commissioned by OTAG (12). It

should be noted that these modeling analyses were conducted to address

1-hour attainment problems. Still, the information is expected to be

generally applicable to 8-hour ozone concentrations as well. The

findings from this report which are relevant include:

New York City--a reduction in transport into the New York

area associated with upwind emissions reductions on the order of 75

percent for NOX and 25 percent for VOC along with local VOC

and NOX reductions may be needed for attainment in New York;

Philadelphia--transport appears to be a major component in

peak ozone concentrations in the Philadelphia domain, contributing 90

percent to the peak in one of the scenarios modeled;

Lake Michigan--transported ozone levels coming into the

Lake Michigan area contribute 40-60 percent to the peak concentration

downwind of urban centers in this area; background concentrations in

the range of 80-100 ppb may need to be reduced to around 60 ppb for

attainment in this region;

Southeast Michigan--ozone transport into this area

``contributed significantly to the simulated peak ozone concentrations

on many of the episode days;

St. Louis--predicted ozone concentrations in this area are

sensitive to incoming levels of ozone/precursor transport;

Atlanta--the amount of ozone transported into the area was

found to be one of the factors contributing to the difficulty for this

area to demonstrate attainment;

Richmond--transported ozone contributes to predicted high

ozone on certain episode days, and regional controls on upwind sources

may be necessary to reduce ozone in this area during some of the

episode days modeled;

Charlotte--transported ozone appears to be a ``significant

component'' of ozone in the area during some episodes, particularly

with winds from a northerly direction; and

Nashville--transported ozone was predicted to be a major

contributor to ozone in this area on 1 of the 2 high ozone days

modeled.

In addition to the preceding qualitative analyses, there are

several non-OTAG regional modeling analyses which provide information

on interstate contributions due to transport. First, modeling by EPA

for the OTC, using the Regional Oxidant Model (ROM), examined the

impact of controls outside the OTR on ozone within this region (13).

The results indicate that a 0.15 lb/MMBtu NOX emissions

limit on certain stationary sources outside the OTR, together with

other controls, would likely have the following effects within the OTR:

Reductions of up to 15-18 ppb in daily maximum 1-hour

ozone in the western part of the OTR, and

Reductions of up to 6-9 ppb along the Northeast Corridor

from Washington, DC to northern New Jersey.

Second, a new modeling technique, the ``Comprehensive Air-quality

Model with extensions'' (CAMx), has been developed (14) in an attempt

to identify the contribution of upwind source areas to specific

downwind locations. The Ozone Source Apportionment Technology (OSAT) in

CAMx was used by the Midwest Ozone Group (MOG) to quantify the

contributions of emissions from upwind sources on high ozone

concentrations in the Northeast Corridor and the Lake Michigan area.

The CAMx analysis modeled the OTAG July 1991 episode only and

considered 1-hour ozone predictions above two cut-points: 100 ppb and

120 ppb. Also, the MOG CAMx report (14) did not examine the

contributions from emissions in individual upwind States, but rather,

the analysis examined the impacts of emissions from concentric

geographic ``rings'' upwind of the Northeast Corridor and Lake Michigan

areas. In general, the results are consistent with the OTAG geographic

sensitivity modeling in that much of the contribution to ozone in a

particular multistate area comes from sources within that same

multistate area, considerable contributions also come from sources

outside the multistate area, and anthropogenic NOX emissions

in upwind areas contribute much more to transport than upwind VOC

emissions. Some of the findings from the CAMx analysis relative to the

contributions to high ozone in the Northeast Corridor and Lake Michigan

area are as follows:

On average, nearly 50 percent of the high ozone levels in

these two areas come from upwind (mostly NOx) sources;

On average, for the Northeast Corridor a large portion (90

percent) of the contribution from upwind sources comes from States to

the west and south within approximately 390 km of the Corridor (this

may include all or portions of States as far upwind as Ohio, North

Carolina, and West Virginia); nearly all (95 percent) of the

contribution comes from upwind sources within approximately 570 km of

the Corridor (this may add portions of Kentucky, Tennessee, and South

Carolina as potential upwind contributors);

On average, for the Lake Michigan area a large portion (90

percent) of the contribution from upwind sources

[[Page 60335]]

comes from States to the west and southwest within approximately 650 km

of this area (this may include all or portions of States as far as

Iowa, Minnesota, Missouri, and Tennessee); nearly all (95 percent) of

the contribution comes from upwind sources within approximately 770 km

of the Lake Michigan area (this adds portions of Arkansas, Kansas,

Nebraska, North Dakota, and South Dakota); and

Transport distances for individual high ozone days are

even longer, in some cases, than the episode averages indicated above.

A third non-OTAG modeling study that is relevant to this assessment

was performed by a group of northwest OTAG States (Iowa, Minnesota,

Nebraska, North Dakota, and South Dakota) (15). One part of this study

included modeling similar to the OTAG subregional modeling, except that

``zero-out'' and ``5c'' emissions reductions were applied in various

combinations in these States only, using the OTAG July 1995 episode. In

these runs, emissions in all other States in the OTAG region were

simulated with the 2007 baseline emissions. The modeling results were

analyzed in terms of the contributions of emissions in these five

States to daily maximum 1-hour ozone above 100 ppb in downwind areas.

The results indicate the following:

Emissions in Minnesota, Nebraska, North Dakota, South

Dakota, and the ``Coarse Grid'' portion of Iowa (see Figure II-1)

collectively contribute less than 2 ppb to downwind ozone above 100

ppb; and

Emissions from these States including the ``Fine Grid''

portion of Iowa, contribute in the range of 2 to 6 ppb to ozone above

100 ppb in grid cells downwind near Lake Michigan, Detroit, and

Cincinnati.

Collectively, the studies cited here indicate that:

The meteorological conditions and air trajectories during

regional-scale, high ozone episodes provide the potential for

multistate ozone transport;

Ambient measurements indicate that ozone episodes can have

a large multistate spatial extent within which 1-to 2-day transport may

occur;

Examination of emissions data indicates that numerous

sources of NOX may be contributing to high regional

background ozone concentrations;

State urban-scale modeling analyses for areas in various

portions of the OTAG region indicate that transport from upwind areas

is an impediment to attainment of the NAAQS;

Regional modeling studies indicate contributions to high

ozone in the Northeast Corridor and the Lake Michigan area may come

from States as far away as 570 km and 770 km, respectively; and

Non-OTAG multistate modeling indicates that emissions from

States in the northwest portion of the ``Coarse Grid'' may not make

large contributions to high ozone in downwind States elsewhere in the

OTAG region.

C. Technical Analysis of Significant Contribution

1. Criteria for Determining Significant Contribution

Whether a contribution is ``significant'' depends on the overall

context. There may be no single amount of contribution which could be

considered as a bright line indicator of ``significant'' that would be

applicable and appropriate in all circumstances. As described above,

under one interpretation of the CAA's section 110(a)(2)(D), factors to

be considered in determining whether a contribution is significant

include:

The level of emissions in the area upwind of a

nonattainment area;

The amount of the contribution (ppb above the level of the

standard) made to the downwind nonattainment area;

The transport distance between the upwind source area and

the downwind problem area; and

The geographic extent of the contribution downwind. For

example, ozone is generally the result of emissions of NOX

and VOC from hundreds of stationary sources and millions of vehicles,

each of which is likely to be responsible for much less than 1 percent

of the overall inventory of precursor emissions. A source or group of

sources should not be exempted from treatment as a significant

contributor merely because it may be a small part, in terms of total

emissions, of the overall problem when all or most other contributors,

individually, are also relatively small parts of the overall problem.

This situation, in which a number of individual (and sometimes small)

sources collectively cause a significant impact, is a major aspect of

the contribution issue. The moderate-to-high ozone levels which cover

broad regions are the result of emissions from millions of individual

sources interacting over multiple days. The contribution to downwind

nonattainment results from the cumulative contribution from all sources

involved in this process. Given these issues, it is not appropriate to

define a bright line test for ``significant contribution.'' Rather, EPA

is using a ``weight of evidence'' approach, based on a range of

information, for determining whether a State makes a significant

contribution to downwind nonattainment. The EPA is also proposing a

second, alternative interpretation to section 110(a)(2)(D), under which

the weight of evidence approach incorporates other factors, including

the relative costs of controlling downwind emissions, as described in

section I.D.2.b., Significant Contribution to Nonattainment.

2. Overview of Technical Approach

The findings from the relevant background studies and the OTAG

modeling results provide a basis for concluding that ozone transport

results in interstate contributions to high ozone levels during

multiday episodic conditions within portions of the OTAG region. An

overview of the approach for analyzing this information in an

assessment of States that make a significant contribution to downwind

nonattainment is as follows:

The air quality and modeling analyses cited in section

B.4, Other Relevant Analyses, were considered in a qualitative manner

to identify, from a regional perspective, States which may contribute

to multistate transport;

The results of the OTAG subregional modeling runs were

used to quantify the extent that each subregion contributes to downwind

nonattainment for the 1-hour and/or 8-hour NAAQS; and

State NOX emissions data were used to translate

the findings from the subregional modeling to a State-by-State basis.

The specific model runs used in this analysis include the ``zero-

out'' runs in which all anthropogenic emissions from individual

subregions (comprised of portions of small groups of States) are

removed, and the contributions to downwind ozone are predicted. This

set of model runs was chosen since it provides an appropriate way to

quantify the contribution of the full set of anthropogenic emissions in

one area to ozone concentrations in another. As described in section

B.2, OTAG Strategy Modeling, zero-out runs were made for the 1988 and

1995 episodes only. The results for both episodes were combined in this

assessment. Also, the analysis of emissions data focussed on

NOX since the OTAG and non-OTAG modeling results indicate

that NOX emissions reductions lower ozone transport across

broad portions of the OTAG region, whereas, VOC emissions reductions

have primarily local benefits.

The air quality, modeling, and emissions information was used

[[Page 60336]]

collectively to determine, based on the weight of evidence, which

States make a significant contribution to downwind nonattainment.

3. Identification of Ozone ``Problem Areas''

As described above, in order to quantify the contribution from

upwind States to nonattainment downwind, EPA identified areas which

currently have a 1-hour and/or 8-hour ozone nonattainment problem and

are expected to continue to have a nonattainment problem in the future,

based on modeling. In addition, EPA considered areas which may have a

future maintenance problem for the 8-hour NAAQS. For current

nonattainment areas, EPA used air quality data for the period 1993

through 1995 to determine which counties are violating the 1-hour and/

or 8-hour NAAQS. These are the most recent 3 years of fully quality-

assured data which were available in time for this assessment. A list

of these counties is provided in Tables II-8a and II-8b. The EPA is

reviewing more recent air quality data for 1996 and 1997. In the event

that these data alter the results of this assessment in any meaningful

way, EPA will make the appropriate adjustments to the findings.

Concerning projected future nonattainment areas, EPA used the OTAG

model predictions for the 2007 baseline, as described in section

II.C.5, Approaches for Analyzing Subregional Modeling Data. For ease of

communication, the technical discussions frequently use the term

``nonattainment'' to refer to these areas. It should be noted that this

use of the term ``nonattainment'' in reference to a specific area is

not meant as an official designation or determination as to the

attainment status of the area.

4. Analysis of Air Quality, Trajectory, and Non-OTAG Modeling

Information

The EPA examined the findings from the air quality, trajectory, and

non-OTAG modeling analyses in section B.4. to identify certain States

which may potentially contribute to nonattainment in downwind areas.

First, EPA applied both the lower and upper ends of the OTAG transport

distance scale (i.e., 150 miles and 500 miles (9)) to 1-hour

nonattainment areas in the northern half of the OTAG region. Using the

lower end of the transport scale indicates that the following States

and Washington DC may potentially contribute to ozone in downwind

nonattainment areas: Connecticut, Delaware, Illinois, Indiana,

Kentucky, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New

Jersey, New York, Ohio, Pennsylvania, Rhode Island, Tennessee,

Virginia, West Virginia, Wisconsin and Vermont. Using the upper limit

of transport distance indicates that the following additional States

may potentially contribute to downwind nonattainment areas: Alabama,

Arkansas, Georgia, Iowa, Kansas, Minnesota, Mississippi, Missouri,

Nebraska, North Carolina, Oklahoma and South Carolina. Also, examining

the findings from the non-OTAG regional modeling results (13, 14, 15)

indicates that collectively, a large portion of the contributions to

high ozone in the Northeast Corridor and/or the Lake Michigan area may

come from States as far upwind as: Missouri, North Carolina, Ohio,

Tennessee and West Virginia.

5. Approaches for Analyzing Subregional Modeling Data

The subregional modeling runs provide a method to quantify the

amount of contribution by upwind States to downwind nonattainment. Four

approaches were included in the analysis of subregional modeling

results. Approaches 1 and 2 were designed to address the contribution

to 1-hour nonattainment and Approaches 3 and 4 the contribution to 8-

hour nonattainment. Approaches 1 and 3 examine the contributions in

areas which have both monitored and modeled nonattainment. Approaches 2

and 4 examine the contributions in areas with modeled nonattainment.

The rationale for each approach is described below.

a. Approaches for 1-Hour Nonattainment. Approach 1 was designed to

focus on contributions to areas that have an observed 1-hour ozone

problem and in which the model predicts an ozone problem. In this

regard, the analysis was restricted to those grid cells in the domain

that had 1-hour daily maximum ozone predictions 125 ppb

6 in the 2007 baseline, and were within one of the counties

currently violating the 1-hour NAAQS. However, the requirement that

high ozone predictions spatially coincide with violating counties may

be overly restrictive given the uncertainties in the modeled wind

regimes associated with the regional nature of the meteorological

inputs. Also, the analysis was limited to only two episodes, only one

of which, July 1995, actually occurred during the 3-year period used to

identify the violating counties. Another limitation of Approach 1 was

that it excludes all grid cells that are over water and not touching

any State land areas. This may be too restrictive since, in the real

atmosphere, sea breeze and lake breeze wind flows can transport high

ozone levels that occur over water back on-shore to affect coastal land

areas. This meteorological process, often associated with high ozone

along the shoreline of Lake Michigan and along the New England coast,

is not adequately treated by the regional scale meteorological inputs

used in OTAG. Thus, high concentrations predicted just offshore may be

inappropriately excluded from the analysis. Approach 2 was designed to

address these concerns. In this approach, all grid cells over land that

had a 1-hour daily maximum ozone prediction 125 ppb in the

baseline were included. Also included were grid cells with predictions

125 ppb over each of the Great Lakes and in a band 60 km (5

grid cells) wide along the East Coast.

---------------------------------------------------------------------------

\6\ Values above 124 ppb are considered to be exceedances of the

0.12 ppm 1-hour ozone NAAQS in view of the rounding convention

established for monitoring data whereby ozone concentrations between

125 ppb and 129 ppb are rounded up to 0.13 ppm.

---------------------------------------------------------------------------

b. Approaches for 8-Hour Nonattainment. The two approaches for

assessing contribution for 8-hour nonattainment were similar in design

to those used for 1-hour nonattainment. However, the inconsistency

between the form of the 8-hour NAAQS, which considers 3 years of data,

and the limited predictions available from the OTAG episodes introduced

a complication to the analysis. Basically, it was not possible to use

the model predictions in a way that explicitly matches the 3-year

average of the 4th highest 8-hour form of the NAAQS. Instead, an

analysis was performed to link the model predictions to the NAAQS as

closely as possible. This analysis consisted of comparing the average

4th highest 8-hour concentrations, based on 3 years of ambient data, to

the average 1st, 2nd, 3rd, and 4th highest 8-hour values using ambient

data limited to the three most recent OTAG episodes (i.e., 1991, 1993,

and 1995). The results of this analysis indicate that the average of

the episodic 2nd highest 8-hour ozone concentration corresponds best,

overall, to the average of the 4th highest 8-hour NAAQS.

Approach 3 is intended to focus on the contributions to areas that

have an observed 8-hour ozone problem and where the model predicts an

8-hour ozone problem. The analysis for this approach was restricted to

those grid cells in the domain that had an average (over the 1988 and

1995 episodes) 2nd high 8-hour ozone prediction 85 ppb in

the 2007 baseline, and were within one of the counties currently

violating the 8-

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hour NAAQS. The same technical concerns and limitations discussed above

for Approach 1 are also applicable to Approach 3. To address these

concerns for the 8-hour analysis, Approach 4 was constructed to include

all grid cells that had an average 2nd high 8-hour ozone prediction

85 ppb over land areas, the Great Lakes, and in the offshore

waters, as in Approach 2 for the 1-hour NAAQS. In addition, by

including all grid cells with predicted nonattainment in 2007, Approach

4 provides a way to consider areas which are currently measuring

attainment, but which may become nonattainment for the 8-hour NAAQS in

the future.

c. Methods for Presenting 1-Hour and 8-Hour Assessments. All of the

approaches for both 1-hour and 8-hour nonattainment quantify the

impacts of emissions in each subregion on ozone concentrations in

downwind States (i.e., States outside the particular subregion). It

should be noted that the calculated contributions represent the impacts

from individual upwind subregions and not the cumulative impacts from

multiple subregions, which would be even greater in magnitude. In

Approaches 2 (1-hour) and 4 (8-hour), grid cells off the East Coast

were added to the totals of the adjacent States, whereas the impacts

for areas over each of the Great Lakes were tabulated separately. In

all cases, the ozone impacts were quantified by calculating the

difference in predicted ozone between each subregional zero-out run and

the 2007 baseline scenario. The contributions from emissions in each

subregion to nonattainment in downwind States are summarized for all

approaches in Tables II-9a and II-9b. This summary shows the

contributions in terms of both the frequency of impacts and the number

of downwind States impacted for specific concentration ranges, as

described below. More detailed information including the contributions

to individual States is provided in Tables II-10 through II-13, for

Approaches 1 through 4, respectively. The contributions are grouped

into one of six ranges: >2 to 5 ppb, >5 to 10, >10 to 15, >15 to 20,

>20 to 25, and >25 ppb. A value of 2 ppb was chosen as the minimum

level for this analysis following the convention generally used by OTAG

for evaluating the impacts of emissions changes. As an example, Table

II-10 shows the frequency of contributions from each subregion to

nonattainment in downwind States for Approach 1. Note that the

frequency of contributions for the 1-hour NAAQS is determined by

tallying the total ``number of days and grid cells'' with impacts

within the specified range. However, the frequency of contributions for

the 8-hour NAAQS includes the total ``number of grid cells'' only. That

is, the averaging procedure used to reflect the form of the 8-hour

NAAQS results in a single ``average'' value for each grid cell, instead

of values for each day modeled. In the following sections, Approach 1

and Approach 3 are referred to as the ``violating-county'' approaches,

whereas Approach 2 and Approach 4 are referred to as the ``all grid-

cell'' approaches for the 1-hour and 8-hour NAAQS, respectively. Also,

as mentioned previously, the term ``nonattainment'' is used to refer to

those areas (grid cells) which meet the criteria for a given approach.

For example, in the analysis of Approach 1, ``nonattainment'' refers to

those areas which have both measured violations and model predictions

of 1-hour ozone 125 ppb.

6. Contributions to 1-Hour Nonattainment

The information from the subregional modeling analyses provided in

Tables II-10 and II-11 were examined from both a ``receptor'' and

``source'' perspective. The results for the ``county-violation''

approach (Approach 1--Table II-10) and the ``all grid-cell'' approach

(Approach 2--Table II-11) are both considered. Examining the data in

Table II-10 indicates that many nonattainment areas are affected by

multiple source areas. Considering the impacts on violating counties

indicates, for example, that:

Nonattainment areas in Pennsylvania receive contributions

of more than 2 ppb from Midwest and Southeast States located in five

subregions (2, 5, 6, 7, and 8) with contributions over 25 ppb from

States in subregions 6 and 7;

Nonattainment areas in New Jersey receive contributions of

more than 2 ppb from Midwest States as well as adjacent States in six

subregions (1, 2, 3, 5, 6, and 7) with contributions over 25 ppb from

subregions 3 and 7;

Nonattainment areas in Maryland receive contributions of

more than 2 ppb from Midwest States and adjacent States in six

subregions (1, 2, 3, 4, 5, and 6) with contributions in the range of 15

to 20 ppb from subregions 3 and 6;

Nonattainment areas in Illinois receive contributions of 5

to 10 ppb from Southeast States in subregion 9; and

Nonattainment areas in Georgia and Alabama receive

contributions of 15 to 20 ppb from Midwest States in subregion 5 as

well as from adjacent Southeast States in subregion 8.

Considering the ``all grid cell'' approach increases the frequency

and magnitude of impacts, as would be expected. For example, the

contributions from States in subregion 2 to nonattainment in

Pennsylvania increase to the range of 10 to 15 ppb; contributions from

Southeast States in subregion 9 in the range of 2 to 5 ppb are evident

in nonattainment in Maryland; and Midwest States in subregions 1 and 5

contribute 5 to 10 ppb to nonattainment in Ohio.

As indicated above, the subregional modeling results were also

examined in terms of the impact of each subregion on ozone in downwind

States outside the particular subregion. The following results

highlight the contributions of each subregion to downwind nonattainment

(see Tables II-10 and II-11). Results are presented for the ``violating

county'' approach (Approach 1) and supplemented with results from the

``all grid-cell'' approach (Approach 2) to the extent that this later

approach adds key information to the findings.

Subregion 1 (portions of Illinois, Wisconsin, Indiana, and Iowa):

emissions in this subregion contribute 2 to 5 ppb on numerous occasions

to nonattainment in violating counties in four States along the

Northeast Corridor having serious or severe nonattainment (i.e.,

Connecticut, Maryland, New Jersey, and New York); downwind

contributions as high as 5 to 10 ppb are evident near Detroit over Lake

St. Clair, as well as over Lakes Erie and Ontario based on the ``all

grid-cell'' approach.

Subregion 2 (portions of Michigan, Indiana, and Ohio): emissions in

this subregion contribute 5 to 10 ppb to nonattainment in violating

counties in five downwind States; contributions over 10 ppb are evident

in seven downwind States from the ``all grid-cell approach.''

Subregion 3 (portions of Pennsylvania, New York and Delaware):

emissions in this subregion contribute over 2 ppb to violating counties

in nine downwind States with contributions of 15 ppb or more in three

States.

Subregion 4 (New Jersey, Connecticut and portions of New York,

Pennsylvania and Delaware): emissions from this subregion contribute

more than 25 ppb on numerous occasions to three downwind States along

the Northeast Corridor.

Subregion 5 (portions of Illinois, Indiana, Kentucky, Missouri, and

Tennessee): emissions from this subregion contribute 2 to 5 ppb to

violating counties in three downwind States along the Northeast

Corridor with contributions of over 10 ppb in three other downwind

States in the region;

[[Page 60338]]

considering the ``all grid-cell'' approach shows contributions of over

20 ppb to the south in Alabama and 5 to 10 ppb over Lakes Erie and St.

Clair.

Subregion 6 (portions of Ohio, Indiana, Kentucky, Tennessee, West

Virginia and Virginia): emissions in this subregion contribute over 5

ppb to violations in eight States (and as far downwind as Massachusetts

with the ``all grid-cell'' approach); contributions over 15 ppb are

predicted in two of the eight States.

Subregion 7 (Maryland, Washington, DC, and portions of Delaware,

North Carolina, Virginia and West Virginia): emissions in this

subregion contribute more than 15 ppb to violating counties in downwind

States along the Northeast Corridor with over 25 ppb contribution on

numerous occasions to two of these States; the ``all grid-cell''

approach indicates contributions from this subregion to South Carolina

as well as to Kentucky and Ohio.

Subregion 8 (portions of North Carolina, South Carolina and

Georgia): emissions in this subregion contribute 2 to 5 ppb to

violating counties in four States including several which are

relatively far downwind (i.e., Missouri and Illinois) with

contributions over 15 ppb to one other State; considering the ``all

grid-cell'' approach indicates contributions of over 10 ppb to two

States along the Northeast Corridor.

Subregion 9 (portions of Tennessee, Georgia, Alabama, Mississippi,

North and South Carolina and Arkansas): emissions in this subregion

contribute over 2 ppb to violating counties in four downwind States

with contributions over 10 ppb in Indiana; contributions over 10 ppb

are evident in three downwind States and far away as Lakes Michigan

from the ``all grid-cell'' approach.

Subregion 10 (Florida and portions of Mississippi, Alabama, Georgia

and Louisiana): emissions in this subregion do not contribute above 2

ppb to violating counties in any other States; considering the ``all

grid-cell'' approach indicates one occurrence of a contribution in the

range of 2-5 ppb.

Subregion 11 (portions of Texas, Louisiana, Arkansas and Oklahoma):

emissions in this subregion contribute 2 to 5 ppb to violating counties

in two downwind States.

Subregion 12 (portions of Missouri, Iowa, Wisconsin, Minnesota,

North Dakota, South Dakota, Nebraska, Kansas and Oklahoma): emissions

in this subregion contribute 2 to 5 ppb in violating counties in two

downwind States with 5 to 10 ppb contributions also evident in one of

these States (i.e., Michigan, including Lake Michigan).

The results presented in Tables II-10 and II-11, and discussed

above, indicate that in general, large contributions to downwind

nonattainment occur on numerous occasions even though the analysis was

limited to only two episodes. Although the level of contribution varies

from subregion to subregion, a consistent pattern is apparent. In view

of the relatively high magnitude of the contributions, and/or the

relatively high frequency of the contributions, and/or the distance

downwind to which the contributions occur, and/or the geographic extent

of the downwind contributions, EPA believes that emissions from

subregions 1 through 9 make a marked contribution to 1-hour

nonattainment in numerous downwind States. Contributions to downwind

nonattainment were also evident from subregions 10, 11, and 12,

although to a lesser magnitude and extent.

7. Contributions to 8-Hour Nonattainment

In general, the downwind contributions to 8-hour nonattainment are

more geographically extensive than those for 1-hour nonattainment. This

is not unexpected because there are many more violating counties for

the 8-hour NAAQS and, likewise, the model predicts ``nonattainment''

over a much broader portion of the region. The following examples

illustrate the extent and magnitude of contributions to violating

counties (Approach 3--Table II-12) that are beyond what was found for

the 1-hour assessment:

Contributions to nonattainment areas in Pennsylvania from

States in subregion 2 are over 25 ppb rather than 2 to 5 ppb;

In addition to the contributions from States in subregions

1, 2, 3, 5, 6, and 7 (ranging up to 15 to 20 ppb from subregion 3),

nonattainment areas in New Jersey also receive a 2 to 5 ppb impact from

southeastern States in subregion 8;

Nonattainment areas in Illinois receive contributions of 5

to 10 ppb from States to the east in subregion 6 and south in subregion

9;

Nonattainment areas in Ohio receive contributions of 5 to

10 ppb from States in five subregions in the Midwest, Northeast, and

Southeast (1, 3, 5, 7, 8, 9) with contributions over 10 ppb from States

in subregion 5;

Nonattainment areas in North Carolina receive

contributions of 5 to 10 ppb from two subregions (7 and 9) with

contributions of over 25 ppb from Midwest States in subregion 6; and

Nonattainment areas in Tennessee receive contributions of

10 to 15 ppb from three subregions (5, 6, and 8) with 15 to 20 ppb

contributed by Midwest States in subregion 6.

Highlights of the 8-hour contributions from a ``source''

perspective are given below based on the information in Tables II-12

and II-13. The following discussion is structured similar to that for

the 1-hour nonattainment analysis in that results are presented for the

``violating county'' approach and supplemented with results from the

``all grid-cell'' approach.

Subregion 1 (portions of Illinois, Wisconsin, Indiana, and Iowa):

emissions in this subregion contribute over 25 ppb to nonattainment in

Michigan with contributions of 5 to 10 ppb in Ohio as well as

contributions of 2 to 5 ppb to six other States.

Subregion 2 (portions of Michigan, Indiana, and Ohio): emissions in

this subregion contribute 2 to 5 ppb to 16 States as far downwind as

New Hampshire and Maine with contributions of 5 to 10 ppb or more in

five States.

Subregion 3 (portions of Pennsylvania, New York and Delaware):

emissions in this subregion contribute 10 to 15 ppb to three States

along the Northeast Corridor with contributions of 5 to 10 ppb in

Massachusetts and New Hampshire.

Subregion 4 (New Jersey, Connecticut and portions of New York,

Pennsylvania and Delaware): emissions from this subregion contribute

over 25 ppb to Rhode Island and Massachusetts with contributions of 15

to 20 ppb in Maine.

Subregion 5 (portions of Illinois, Indiana, Kentucky, Missouri, and

Tennessee): emissions from this subregion contribute 2 ppb or more to

13 States with contributions of 10 to 15 ppb in two States.

Subregion 6 (portions of Ohio, Indiana, Kentucky, Tennessee, West

Virginia and Virginia): emissions in this subregion contribute 5 to 10

ppb or more to 10 States with contributions of 15 ppb or more in two

States.

Subregion 7 (Maryland, Washington, DC, and portions of Delaware,

North Carolina, Virginia and West Virginia): emissions in this

subregion contribute 10 to 15 ppb or more to four States with

contributions of 5 to 10 ppb as far downwind as Rhode Island and

Massachusetts and 2 to 5 ppb in Maine.

Subregion 8 (portions of North Carolina, South Carolina and

Georgia): emissions in this subregion contribute 10 to 15 ppb to three

States and 15 to 20 ppb to one of these States; multiple contributions

of 2 to 5 ppb are predicted as far downwind as New Jersey.

Subregion 9 (portions of Tennessee, Georgia, Alabama, Mississippi,

North

[[Page 60339]]

and South Carolina and Arkansas): emissions in this subregion

contribute 5 to 10 ppb to six States with contributions of 10 to 15 ppb

in two States.

Subregion 10 (Florida and portions of Mississippi, Alabama, Georgia

and Louisiana): emissions in this subregion contribute 2 to 5 ppb in

two States and 5 to 10 ppb in one State.

Subregion 11 (portions of Texas, Louisiana, Arkansas and Oklahoma):

emissions in this subregion contribute 2 to 5 ppb in six States.

Subregion 12 (portions of Missouri, Iowa, Wisconsin, Minnesota,

North Dakota, South Dakota, Nebraska, Kansas and Oklahoma): emissions

in this subregion contribute 2 to 5 ppb in three States; considering

the ``all grid-cell'' approach indicates multiple contributions of 2 to

5 ppb downwind over Lake Michigan and Lake Erie.

The results indicate that the contributions to 8-hour nonattainment

are very consistent with those for 1-hour nonattainment. Subregions 1

through 9 have a much greater magnitude, frequency, and geographic

extent of contribution compared to the other subregions. Thus, based on

this assessment, EPA believes that emissions from subregions 1 through

9 make a marked contribution to downwind nonattainment for the 8-hour

NAAQS. In fact, the extent of contributions from most of these

subregions (i.e., 1 through 9) is even larger for 8-hour nonattainment

while the contribution from the other subregions (i.e., 10, 11, and 12)

still remains relatively low by comparison.

8. Assessment of State Contributions

The preceding air quality, trajectory, emissions, and modeling

analyses provide a number of pieces of information for determining,

based on the weight of evidence, which States make a significant

contribution to downwind nonattainment. The assessment of the State

contributions is divided into three parts. States which are wholly or

partially contained within subregions 1-9 are considered first since

emissions from these States make a marked contribution to downwind

nonattainment for both the 1-hour and 8-hour NAAQS, based upon the

subregional modeling. States which were not included in any of the OTAG

subregions (i.e., some of the New England States) are considered

second. States located in subregions 10, 11 and 12, which did not have

a marked contribution to downwind nonattainment for either the 1-hour

or 8-hour NAAQS, are discussed last.

The subregional modeling results indicate that emissions from

States in subregions 1 through 9 produce large downwind contributions

in terms of the magnitude, frequency, and geographic extent of the

downwind impacts. In addition, nonattainment areas within many States

in the OTAG region receive large and/or frequent contributions from

emissions in these subregions. The EPA believes that the following

States whose emissions are wholly or partially contained within one or

more of these subregions (i.e., Alabama, Connecticut, Delaware,

Washington DC, Georgia, Illinois, Indiana, Kentucky, Maryland,

Michigan, Missouri, New Jersey, New York, North Carolina, Ohio,

Pennsylvania, South Carolina, Tennessee, Virginia, West Virginia, and

Wisconsin) is making a significant contribution to downwind

nonattainment. In addition to the marked levels of contributions

described above, this finding is based on:

OTAG strategy modeling and non-OTAG modeling indicates

that NOX emissions reductions across these States would

produce large reductions in 1-hour and 8-hour ozone concentrations

across broad portions of the region including 1-hour and 8-hour

nonattainment areas;

The air quality, trajectory, and wind vector analyses

indicate that these States are upwind from nonattainment areas within

the 1- to 2-day distance scale of transport;

These States form a contiguous area of manmade emissions

covering most of the core portion of the OTAG region;

11 of the States that are wholly within these nine

subregions (i.e., Illinois, Indiana, Kentucky, New Jersey, North

Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Virginia and

West Virginia) have a relatively high level of NOX emissions

from sources in their States; these States are ranked in the top 50

percent of all States in the region in terms of total NOX

emissions and/or have NOX emissions exceeding 1000 tons per

day, as indicated in Table II-1;

States wholly within subregions 1 through 9 with lesser

emissions (i.e., Connecticut, Delaware, Maryland) and Washington, DC

have a relatively high density of NOX emissions, as

indicated in Table II-2;

For the nine States that are only partially contained in

one of subregions 1 through 9 (i.e., Arkansas, Iowa, Michigan,

Mississippi, Missouri, Alabama, Georgia, Wisconsin, and New York) the

State total NOX emissions in Table II-1 as well as each

State's contribution to NOX emissions in the subregions (see

Tables II-14a and II-14b) indicate that six o

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