Catawba County v. Environmental Protection Agency

United States Court of Appeals

FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued April 6, 2009 Decided July 7, 2009

No. 05-1064

CATAWBA COUNTY, NORTH CAROLINA, ET AL.,

PETITIONERS

v.

ENVIRONMENTAL PROTECTION AGENCY,

RESPONDENT

SIERRA CLUB,

INTERVENOR

Consolidated with 05-1065, 05-1067, 05-1068, 05-1069,

05-1071, 05-1072, 05-1073, 05-1075, 05-1076, 05-1077,

05-1078, 05-1184, 05-1190, 05-1196, 05-1200, 05-1202,

06-1049, 06-1052, 06-1083, 06-1088, 06-1102, 06-1172,

07-1412, 07-1417, 07-1418, 07-1428, 07-1465, 07-1467,

07-1530

On Petitions for Review of Final Actions

of the Environmental Protection Agency

Marc D. Machlin argued the cause and filed the briefs for

petitioner Oakland County, Michigan.

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Louis E. Tosi argued the cause for Industry Petitioners.

With him on the briefs were Paul E. Gutermann, Charles L.

Franklin, Douglas A. McWilliams, Allen A. Kacenjar,

Michael E. Born, Cheri Ann Budzynski, Gale Lea Rubrecht,

Kathy G. Beckett, David M. Flannery, and Edward L. Kropp.

Andrew M. Cuomo, Attorney General, Attorney General=s

Office of the State of New York, Michael J. Myers and Jacob

Hollinger, Assistant Attorney Generals, Mark Rudolph,

Senior Counsel, Office of Legal Services, West Virginia,

Steve Carter, Attorney General, Attorney General=s Office of

the State of Indiana, Steve D. Griffin and Valerie Tachtiris,

Deputy Attorneys General, and Thomas M. Fisher, Special

Counsel, were on the briefs of State Petitioners.

Karma Barsam Brown, Phillip L. Conner, Ronald E.

Cardwell, Ethan R. Ware, George William House, S. Kyle

Woosley, and Lewis S. Wiener were on the briefs for County

Petitioners.

Laurel A. Bedig and Monica Derbes Gibson, Attorneys,

and Jon M. Lipshultz, Senior Counsel, U.S. Department of

Justice, argued the cause for respondent. With them on the

brief were John C. Cruden, Deputy Assistant Attorney

General, Jessica O’Donnell, Attorney, and Geoffrey L.

Wilcox, Counsel, U.S. Environmental Protection Agency.

Kenneth C. Amaditz, Attorney, U.S. Department of Justice,

entered an appearance.

David S. Baron and Jennifer C. Chavez were on the brief

for intervenor. Howard I. Fox entered an appearance.

Before: TATEL, GARLAND, and GRIFFITH, Circuit Judges.

Opinion for the Court filed PER CURIAM.

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PER CURIAM: In these consolidated petitions, several

states, counties, and industrial entities challenge the

Environmental Protection Agency’s promulgation of area

designations for the annual national ambient air quality

standard applicable to fine particulate matter, a category of air

pollutants consisting of miniscule airborne particles known

to present adverse health risks. Insisting that EPA’s

methodology for designating areas as “nonattainment” for the

fine particulate matter standard violates section 107(d) of the

Clean Air Act, which governs such designations, and that this

methodology and the individual designations it produced are

otherwise arbitrary and capricious, petitioners ask us to vacate

the nonattainment designations and to send EPA back to the

drawing board. With one minor exception, we deny the

petitions for review. Faced with the complex task of

identifying those geographic areas that contribute to fine

particulate matter pollution, EPA both complied with the

statute and, for all but one of the 225 counties or partial

counties it designated as nonattainment, satisfied—indeed,

quite often surpassed—its basic obligation of reasoned

decisionmaking.

I.

Title I of the Clean Air Act charges EPA with

formulating national ambient air quality standards (NAAQS)

for air pollutants that may reasonably be anticipated to

endanger public health and welfare. 42 U.S.C. §§ 7408–09.

NAAQS set maximum ambient air concentrations for those

pollutants. Id. While each state has “primary responsibility

for assuring air quality” within its borders and, in particular,

for developing a state implementation plan (SIP) for

achieving and maintaining the NAAQS for each air pollutant,

42 U.S.C. § 7407(a), the Act triggers more or less stringent

requirements depending on the quality of an area’s ambient

air. Thus, before a state can design an appropriate SIP, it

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must know which areas within its boundaries comply with the

NAAQS and which do not.

This is where CAA section 107(d) comes in. It requires

EPA to designate areas as “attainment,” “nonattainment,” or

“unclassifiable” depending on their compliance with the

relevant NAAQS. “Attainment” areas are those that meet the

relevant standard; “nonattainment” areas are those that exceed

the standard or that “contribute[] to ambient air quality in a

nearby area” that exceeds the standard; “unclassifiable” areas

are those that permit no determination given existing data.

§ 7407(d)(1)(A)(i)–(iii). In nonattainment areas, the Act

requires stricter pollution controls. For instance, states must

implement controls that will achieve attainment “as

expeditiously as practicable” in nonattainment areas,

id. § 7502(a), (c)(1), whereas states need only implement

measures that will prevent “significant deterioration of air

quality” for attainment and unclassifiable areas, id. § 7471.

In addition to setting the criteria for attainment and

nonattainment, section 107(d)(1) prescribes the designation

process. Upon promulgation of new or revised NAAQS,

states must submit to EPA their own “initial designations” of

all areas within their borders. § 7407(d)(1)(A). EPA must

then promulgate the submitted designations or modify them as

it deems necessary. § 7407(d)(1)(B). Specifically, CAA

section 107(d)(1)(B)(ii) provides that:

In making the promulgations required . . . , the

Administrator may make such modifications

as the Administrator deems necessary to

the designations of the areas (or portions

thereof) submitted [by the states] under

subparagraph (A) (including to the boundaries

of such areas or portions thereof). Whenever

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the Administrator intends to make a

modification, the Administrator shall notify

the State and provide such State with

an opportunity to demonstrate why any

proposed modification is inappropriate. The

Administrator shall give such notification no

later than 120 days before the date the

Administrator promulgates the designation,

including any modification thereto.

§ 7407(d)(1)(B)(ii).

This case involves the NAAQS for fine particulate

matter. Known as PM2.5, fine particulate matter consists of

airborne particles that are 2.5 micrometers in diameter or

smaller—i.e., less than one-thirtieth the thickness of a human

hair. Air Quality Designations and Classifications for the

Fine Particles (PM2.5) National Ambient Air Quality

Standards (“PM2.5 Designations Rule”), 70 Fed. Reg. 944,

945 (Jan. 5, 2005) (codified at 40 C.F.R. pt. 81). A

“significant association” links elevated levels of PM2.5 with

adverse human health consequences such as premature death,

lung and cardiovascular disease, and asthma. Id. And

significantly for the primary issue before us—EPA’s method

for identifying the geographic origins of elevated ambient

PM2.5 concentrations—PM2.5 can travel hundreds or thousands

of miles.

In 1997, EPA abandoned its practice of regulating all

particulate matter, both coarse and fine, under a unified

standard. Instead it established specific PM2.5 NAAQS for the

first time. National Ambient Air Quality Standards for

Particulate Matter, 62 Fed. Reg. 38,652 (July 18, 1997).

EPA promulgated annual and 24-hour PM2.5 NAAQS, setting

the annual standard—the one at issue here—at 15 micrograms

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per cubic meter. Id. at 38,677; see also 40 C.F.R. § 50.7.

Although section 107(d) required EPA to promulgate area

designations for the new standard “as expeditiously as

possible,” § 7407(d)(1)(B)(i), litigation here and in the

Supreme Court waylaid the designation process until we

finally upheld the standard five years later. See Am. Trucking

Ass’ns v. EPA, 283 F.3d 355 (D.C. Cir. 2002), on remand

from Whitman v. Am. Trucking Ass’ns, 531 U.S. 457 (2001),

aff’g in part and rev’g in part Am. Trucking Ass’ns v. EPA,

175 F.3d 1027 (D.C. Cir. 1999). In the meantime, Congress

had passed legislation requiring the deployment of a

nationwide PM2.5 monitoring network and extending the

deadline for the designations until three years of monitoring

data had been collected. See Transportation Equity Act for

the 21st Century (“TEA-21”), Pub. L. No. 105-178, §§ 6101–

02, 112 Stat. 107, 463–65 (1998). Then, following our

decision upholding the PM2.5 NAAQS and EPA’s initiation of

the designation process, Congress amended the Clean Air Act

to add section 107(d)(6), which set a firm deadline for the

PM2.5 area designations. See Pub. L. No. 108-199, § 425(a),

118 Stat. 3, 417 (2004) (codified at § 7407(d)(6)). Thus,

amended section 107(d)(6)(A) now provides:

Notwithstanding any other provision of law,

not later than February 15, 2004, the Governor

of each State shall submit designations referred

in paragraph (1) for the July 1997 PM2.5

national ambient air quality standards for each

area within the State, based on air quality

monitoring data collected in accordance with

any applicable Federal reference methods for

the relevant area.

§ 7407(d)(6)(A). And section 107(d)(6)(B) provides:

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Notwithstanding any other provision of law,

not later than December 31, 2005, the

Administrator shall, consistent with paragraph

(1), promulgate the designations referred to in

subparagraph (A) for each area of each State

for the July 1997 PM2.5 national ambient air

quality standards.

§ 7407(d)(6)(B).

In April 2003, EPA issued a guidance document initiating

the PM2.5 designation process. Known as the Holmstead

Memo, the document explains the timeline for state

submissions and, more importantly, the criteria EPA would

employ in reviewing those submissions. Memorandum from

Jeffrey R. Holmstead, Assistant Administrator, to Regional

Administrators, Regions I–X (Apr. 1, 2003) (“Holmstead

Memo”). Noting “recent evidence that violations of the PM2.5

air quality standards generally include a significant urban-

scale contribution,” the Holmstead Memo explains EPA’s

“inten[t] to apply a presumption that the boundaries for urban

nonattainment areas should be based on Metropolitan Area

boundaries.” Id. at 2. In other words, the Memo announces

EPA’s view that if any area within a metropolitan area

exceeds the annual PM2.5 NAAQS, then all areas within the

metropolitan area presumptively “contribute” to that violation

within the meaning of section 107(d)(1)(A) and therefore

warrant “nonattainment” designations. The Holmstead Memo

further explains that EPA would define metropolitan

boundaries by reference to Office of Management and Budget

definitions of metropolitan statistical areas (MSAs) and

consolidated metropolitan statistical areas (CMSAs)

(interchangeably, “C/MSAs”). Id. Thus, under this approach,

a violation of the PM2.5 NAAQS in the District of Columbia,

for instance, would trigger the presumption that seventeen

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counties in northern Virginia and five counties in Maryland—

all inside the applicable MSA, though only some are

contiguous with the District—contribute to elevated PM2.5

levels in the city and warrant “nonattainment” designations.

An attachment to the Holmstead Memo elaborates on

EPA’s basis for adopting the presumption, as well as the

circumstances that would warrant a departure. As to the

rationale for the presumption, the Holmstead Memo explains

that after “examin[ing] the geographic distribution of total

PM2.5 concentrations in and near many metropolitan areas,”

the agency had “found an association of higher PM2.5

concentrations with greater levels of urban activity” such as

“motor vehicle use and home heating[,] as well as industrial

activities.” Holmstead Memo, Attach. 2, Guidance on

Nonattainment Area Designations for PM2.5, at 4–5

(“Holmstead Memo Guidance”). Thus, “[the] presumption

reflects EPA’s view that, in the absence of evidence to the

contrary, violations of the PM2.5 NAAQS in urban areas may

be presumed attributable at least in part to contributions from

sources distributed throughout the Metropolitan Area.” Id. at

5. That said, the Holmstead Memo also recognizes that

appropriate boundaries of urban nonattainment areas may

well be smaller or larger than the applicable C/MSA. EPA

would therefore “consider requests for urban nonattainment

area definitions that deviate from OMB’s metropolitan area

definitions on a case-by-case basis.” Id. at 6. The Holmstead

Memo lists nine factors to guide that case-by-case analysis:

(1) emissions in the potentially contributing areas; (2) air

quality in those areas; (3) population density and degree of

urbanization in those areas; (4) traffic and commuting

patterns; (5) expected growth; (6) meteorology; (7) geography

and topography; (8) jurisdictional boundaries; and (9) level of

control of emissions sources. Id. at 7. The Memo encourages

states submitting designations that depart from the

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metropolitan presumption to justify such designations by

reference to all nine factors. Id.

With that, the designation process was underway. The

states submitted their initial designations; EPA responded

with its proposed modifications, as well as explanations of its

analysis under the nine-factor test; the states then submitted

any responses; and EPA promulgated the final area

designations in December 2004. See PM2.5 Designations

Rule, 70 Fed. Reg. at 946. In a technical support document

accompanying the Rule, EPA explained the basis for the

designations and the analytical tools that it had developed and

applied to assess the nine factors. See EPA, Office of Air

Quality Planning and Standards, Technical Support Document

for State and Tribal Air Quality Fine Particle (PM2.5)

Designations (2004) (“Technical Support Document”).

Recognizing that 2004 monitoring data would soon become

available, EPA also invited states to submit any new data that

might support an amended designation. PM2.5 Designations

Rule, 70 Fed. Reg. at 948. Based on the new data, EPA then

revised designations for eight areas from nonattainment to

attainment and four areas from unclassifiable to attainment.

See Air Quality Designations for the Fine Particles (PM2.5)

National Ambient Air Quality Standards—Supplemental

Amendments, 70 Fed. Reg. 19,844, 19,844 (Apr. 14, 2005)

(codified at 40 C.F.R. pt. 81).

In the end, EPA applied the C/MSA presumption so that

nonattainment boundaries were coextensive with metropolitan

boundaries (and unchanged by the nine-factor analysis) in

only seven of thirty-nine metropolitan areas. See EPA Br. 54

(citing relevant portions of the Technical Support Document).

In every other metropolitan area, applying the nine-factor

analysis and finding that the presumption misjudged the

nature of the PM2.5 problem, EPA designated the urban

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nonattainment area as either an area larger than the OMB-

defined metropolitan area (for instance, in Chattanooga,

Tennessee) or smaller (for instance, in Washington, DC).

Several states, local governments, and industrial entities

petitioned EPA for reconsideration of the designations; others

filed petitions for review directly in this court. We stayed

proceedings in this court while EPA considered the petitions

for reconsideration. Once EPA resolved the petitions for

reconsideration, we consolidated all petitions for review.

Petitioners’ challenges fall into four broad categories.

First, they raise procedural challenges to the Holmstead

Memo and to the Designations Rule, arguing that EPA

illegally bypassed notice and comment for each. Second, they

raise various objections to EPA’s statutory authority to adopt

and implement the C/MSA presumption and the nine-factor

test. Third, they argue that even if section 107(d) permits

EPA to adopt the C/MSA presumption and the nine-factor

test, EPA’s analysis nonetheless suffers from such serious

methodological deficiencies and inconsistencies as to render

the entire Designations Rule arbitrary and capricious. Finally,

as a last resort, petitioners request that we vacate certain area

designations that affect them, claiming that EPA at least acted

arbitrarily and capriciously in making these particular

nonattainment and unclassifiable designations. We review

petitioners’ challenges under section 307(d)(9) of the Clean

Air Act, which requires the court to set aside EPA’s final

actions when they are in excess of the agency’s statutory

authority or otherwise arbitrary and capricious. 42 U.S.C. §

7607(d)(9)(a).

II.

Before addressing petitioners’ arguments, however, we

think it helpful to review some technical background.

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Fine particulate matter includes both “primary” particles

(e.g., carbonaceous particles and so-called “crustal” particles

like dust) that pollution sources emit directly into the

atmosphere, as well as “secondary” particles (e.g., sulfate and

nitrate particles) that form in the atmosphere as a result of

chemical reactions between PM2.5 precursors that sources

emit. PM2.5 Designations Rule, 70 Fed. Reg. at 945. Power

plants, diesel and gasoline powered engines in mobile sources

like cars and trucks, and other industrial sources produce most

carbonaceous particles; agriculture, mining, and other

activities that cause soil or metals to be suspended in the

atmosphere account for the crustal component. See Technical

Support Document § 3.1; EPA, Office of Air Quality and

Planning Standards, The Particle Pollution Report 6 (2004),

available at http://www.epa.gov/air/airtrends/aqtrnd04/pm.

html. The chemical precursors to secondary PM2.5 include

sulfur dioxide (SO2), emitted in substantial part by power

plants; nitrogen oxides (NOx), emitted in substantial part by

mobile sources, power plants, and other industrial sources;

and ammonia, emitted from agricultural sources, mobile

sources, and power plants. See PM2.5 Designations Rule, 70

Fed. Reg. at 945; Technical Support Document § 3.1.

Atmospheric chemical reactions between these gases yield

secondary PM2.5 in the form of sulfate and nitrate particles.

PM2.5 Designations Rule, 70 Fed. Reg. at 945. The PM2.5

NAAQS set a 15µg/m3 annual limit for all fine particulate

matter without distinguishing among the various kinds (or

“species”) of PM2.5. Even so, “speciation data” that breaks

the total PM2.5 concentration into its constituent components

is quite useful for the area designation process. Because such

data reveals the kinds of particles (carbon, sulfate, nitrate,

crustal particles, etc.) that most account for an area’s PM2.5

problem, it suggests, by extrapolation, the kinds of sources

most responsible for the problem as well.

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While the Holmstead Memo announced EPA’s

methodology for determining whether an area with passable

PM2.5 concentrations nonetheless deserves a “nonattainment”

designation, EPA regulations set forth the technical

procedures for measuring ambient PM2.5 concentrations in the

first place. Exhaustive technical specifications regulate the

states’ operation of a network of air monitors that collect air

quality data for any given area. See 40 C.F.R. pt. 50, Apps.

L, N. These monitors measure ambient PM2.5 concentration,

what’s called the “design value,” on any given day. The

annual design value—which determines whether an area

complies with the PM2.5 standard—is then computed by

averaging every quarter’s worth of daily design value samples

(typically collected every third or sixth day), averaging those

quarterly numbers to obtain an annual average, and then

averaging three years of annual numbers to yield the final

annual design value. See 40 C.F.R. pt. 50, App. N. Samples

from these monitors can be further analyzed to yield the

speciation data described above.

The majority of the PM2.5 designations at issue here drew

on monitoring data collected from 2001 to 2003. Based on a

judgment that no petitioner challenges, EPA decided that “the

county boundary . . . [would] determin[e] the extent of the

area reflected by [a violating] PM2.5 monitor.” PM2.5

Designations Rule, 70 Fed. Reg. at 946; see also id. at 946–47

(“[I]f a PM2.5 monitor was violating the standard based on

the 2001–2003 data, at a minimum we designated the county

where that monitor is located as nonattainment. We made

exceptions . . . in a few very large western counties where a

significant geographic feature such as a mountain range

divided a county. . . .”). Thus, for instance, if a monitor in an

industrial area of downtown Detroit registered a violation, all

of Wayne County would be designated as nonattainment—

including even its more idyllic corners like the town of

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Grosse Pointe. Cf. id. at 980 (designating Wayne County

nonattainment). To be clear, this reflects quite a separate

judgment from that underlying the C/MSA presumption.

EPA’s selection of the county as the unit of analysis resolved

a problem inherent in the monitoring process, namely, that a

monitor only measures air quality in its immediate vicinity.

Because of this, EPA had to determine how much compass to

give any monitored measurement, which it did by choosing

the county as the unit of analysis. The C/MSA presumption,

by contrast, addresses a different problem, namely, how to

identify those areas that, although deemed to be meeting the

standard themselves, are contributing to nearby violations.

We’ve already described the nine factors that EPA

evaluated to determine whether to depart from the C/MSA

presumption, see supra at 8, and in the hundreds of pages that

comprise the Technical Support Document, EPA explained its

findings for each metropolitan area on each of the nine

factors. EPA assessed these factors with the help of several

analytical tools and models it had developed. See Technical

Support Document §§ 3.0–5.9 (explaining analytical tools).

We describe the most important ones here in general fashion,

reserving additional elaboration for those portions of the

opinion that require it.

To start, given the hundreds of miles that PM2.5 can travel

in the atmosphere, EPA thought it important to isolate the

portion of urban PM2.5 that originates from a metropolitan

area’s local sources as opposed to regional sources much

farther away. Thus, under its “urban excess” analysis, EPA

paired an urban monitoring site with an upwind rural

monitoring site—i.e., a rural site where prevailing winds

move in the direction of the metropolitan area—and

“subtract[ed] the rural concentration from the measured

urban concentration.” Id. § 3.1. True to name, this simple

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arithmetic allowed EPA to estimate the portion of urban PM2.5

levels that arises from urban activities by cancelling out the

“rural background” that would exist regardless of those

activities. Id. EPA calculated the urban excess for each

PM2.5 species and then summed those numbers to yield a total

urban excess measure. Id. § 3.2.

EPA next used the urban excess calculations to develop

“weighted emissions scores” for each county in a C/MSA. Id.

§ 4.0. The notion underlying these scores is intuitive: if the

urban excess numbers for the District of Columbia, for

instance, reveal that all local PM2.5 pollution is in the form of

carbon, it would make little sense to think that a C/MSA

county plays a significant part in the District’s monitored

violation if the county has zero carbon emissions. Thus, for

purposes of evaluating the first of the nine factors—the

“emissions in areas potentially included versus excluded,”

Holmstead Memo Guidance at 7—EPA determined that raw

emissions data is usually less suggestive of contribution than

data adjusted to account for the PM2.5 species that actually

comprise the urban excess.

Calculating weighted emissions scores required a number

of steps. See Technical Support Document §§ 4.1–4.3. First,

EPA determined the total metropolitan emissions of carbon,

SO2, NOx, and crustal particles by summing the counties’

individual emissions of each pollutant. For those pollutants,

EPA then divided each county’s emissions by total C/MSA

emissions, calculating each county’s percentage share of total

metropolitan emissions. For example, if County A emits 50

tons of carbon and total C/MSA carbon emissions equal 100

tons, then the ratio would be fifty percent. Next EPA

“weighted” these percentages by multiplying them by the

proportion of urban excess attributable to the relevant

pollutant. To continue with our hypothetical, then, if carbon

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accounted for forty percent of urban excess, EPA would

multiply fifty percent by four-tenths, and County A’s

weighted carbon score would be twenty. Having calculated a

county’s weighted scores for each PM2.5 species, EPA then

added these scores together to derive a county’s total

weighted emissions score. Importantly, because these scores

scale a county’s raw emissions based on attributes specific to

an individual C/MSA—i.e., the urban excess number and the

total level of metropolitan emissions—they only provide a

measure for comparing counties within the same C/MSA.

Finally, EPA developed so-called “pollution roses”

that depict 2001–2003 monitoring and meteorological data

for each PM2.5 air monitor. See, e.g., Technical Support

Document 6-11 to -12. Each pollution rose consists of

concentric circles, with the circles’ center representing the

location of the air monitor. EPA then plotted dots around the

circles, with each dot representing one monitored reading, the

dot’s size representing the magnitude of the reading, the dot’s

spatial location representing the prevailing wind direction on

the day of the reading, and the dot’s distance from the center

of the circle representing the average wind speed on that day.

With this technical background in mind, we turn to

petitioners’ four primary arguments.

III.

Petitioners first lodge procedural challenges against

EPA’s promulgation of the final designations rule and the

Holmstead Memo. Petitioners argue that EPA violated the

Administrative Procedure Act, 5 U.S.C. § 553, by failing to

publish both the Rule and the Holmstead Memo for notice and

comment. They are in error as to both.

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A. Final Designations Rule

Designation of nonattainment areas is governed by

section 107(d) of the Clean Air Act. § 7407(d). The parties

disagree as to which subsection of section 107(d) provides

EPA’s authority to promulgate designations. Industry

petitioners argue that designations are promulgated under

section 107(d)(6), which states: “Notwithstanding any other

provision of law, not later than December 31, 2004, the

Administrator shall, consistent with paragraph (1), promulgate

the designations referred to in subparagraph (A) for each area

of each State for the July 1997 PM2.5 national ambient air

quality standards.” § 7407(d)(6)(B). By contrast, EPA argues

that the source of its authority is a provision of section

107(d)(1), entitled “Promulgation by EPA of designations,”

which states in relevant part:

Upon promulgation or revision of a national

ambient air quality standard, the Administrator

shall promulgate the designations of all areas

(or portions thereof) submitted under

subparagraph (A) as expeditiously as

practicable, but in no case later than 2 years

from the date of promulgation of the new or

revised national ambient air quality standard.

§ 7407(d)(1)(B)(i). The distinction between these provisions

is important because the statute exempts designations

under section 107(d)(1), among others, from the APA’s

section 553 notice-and-comment requirements; it does not,

however, exempt designations under section 107(d)(6). See

§ 7407(d)(2)(B) (“Promulgation or announcement of a

designation under paragraph (1), (4) or (5) shall not be subject

to the provisions of sections 553 through 557 of title 5 of the

United States Code (relating to notice and comment), except

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nothing herein shall be construed as precluding such public

notice and comment whenever possible.”).

EPA is entrusted with administering the Clean Air Act, of

which section 107 is a part, and thus we review the agency’s

construction of the statutory provisions under the familiar

two-step framework set out in Chevron U.S.A. Inc. v. Natural

Resources Defense Council, 467 U.S. 837 (1984). Under

Chevron step one, we ask “whether Congress has directly

spoken to the precise question at issue.” Id. at 842. If at that

point we determine that “the intent of Congress is clear, that is

the end of the matter; for the court, as well as the agency,

must give effect to the unambiguously expressed intent of

Congress.” Id. at 842–43. We proceed to Chevron’s second

step only “if the statute is silent or ambiguous with respect

to the specific issue.” Id. at 843. At the second step, we

determine “whether the agency’s answer is based on a

permissible construction of the statute.” Id.

Here we need go no further than the first step because

the intent of Congress is clear. Petitioners’ reliance

on section 107(d)(6) is misplaced. Subparagraph (B) of

section 107(d)(6) requires that, “not later than December 31,

2004, the Administrator shall . . . promulgate the designations

referred to in subparagraph (A).” § 7407(d)(6)(B).

Subparagraph (A), in turn, states: “Notwithstanding any other

provision of law, not later than February 15, 2004, the

Governor of each State shall submit designations referred to

in paragraph (1) [of § 7407(d)] for the July 1997 PM2.5

national ambient air quality standards . . . .” § 7407(d)(6)(A)

(emphasis added). Thus, contrary to petitioners’ claim,

section 107(d)(6)(B), when read in conjunction with section

107(d)(6)(A), shows that section 107(d)(6) does not itself

authorize the promulgation of designations. Rather, section

107(d)(6) merely governs the timing of PM2.5 designations,

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which are made under the authority contained in section

107(d)(1)—a provision that the statute expressly exempts

from notice-and-comment requirements. See § 7407(d)(2)(B).

B. Holmstead Memo

Petitioners’ argument that the Holmstead Memo had to

undergo notice and comment stems, in part, from their

erroneous belief that the final designations were subject to

notice and comment. Our determination above, that the

statute exempts the nonattainment designations from notice-

and-comment procedures, suggests that the Holmstead

Memo—which was simply the first step in the promulgation

of designations—is also exempt.

Petitioners’ further argument, that the Holmstead Memo

is a legislative rule that must undergo notice and comment

independent of the final rule to which it relates, is also

unavailing. For support, petitioners point to General Electric

Co. v. EPA, 290 F.3d 377 (D.C. Cir. 2002), in which we

explained that whether an agency action is the type of action

that must undergo notice and comment depends on “whether

the agency action binds private parties or the agency itself

with the ‘force of law,’” id. at 382—that is, whether “a

document expresses a change in substantive law or policy

(that is not an interpretation) which the agency intends to

make binding, or administers with binding effect,” id. at 382–

83 (quoting Robert A. Anthony, Interpretive Rules, Policy

Statements, Guidances, Manuals, and the Like—Should

Federal Agencies Use Them to Bind the Public?, 41 DUKE

L.J. 1311, 1355 (1992)). General Electric further explained

that “an agency pronouncement will be considered binding as

a practical matter if it either appears on its face to be

binding . . . or is applied by the agency in a way that indicates

it is binding.” Id. at 383 (internal citation omitted).

19

In response, EPA argues that the Holmstead Memo is

merely a policy statement, not a legislative rule, because it

does not create or modify legally binding rights or

obligations. As EPA correctly notes, the APA expressly

exempts policy statements from notice-and-comment

requirements. See 5 U.S.C. § 553(b)(A) (specifying that,

except when required by statute, the section 553 requirements

for notice and comment do not apply “to interpretative rules,

general statements of policy, or rules of agency organization,

procedure, or practice”).

EPA has the better of this dispute. First, the Holmstead

Memo is not binding on its face. It specifies that it merely

“provides guidance to State and local air pollution control

agencies . . . on the process for designating areas for the

purpose of implementing the fine particle national ambient air

quality standards.” Holmstead Memo at 1. It then explicitly

states that it is “not binding” on the states or EPA and notes

that it provides only EPA’s “current views” on the

designation process, suggesting that those views are open to

revision. Id. at 2. Unlike the agency documents at issue in

General Electric and CropLife America v. EPA, 329 F.3d 876

(D.C. Cir. 2003), which petitioners also cite, the Holmstead

Memo does not impose binding duties on states or the agency.

It merely clarifies the states’ existing duties under the Clean

Air Act and explains the process EPA suggests for states to

follow in providing their initial designations. As we

explained above, see supra at 7–8, the Memo establishes a

rebuttable C/MSA presumption and outlines nine factors for

EPA to consider in its final designations, see Holmstead

Memo Guidance at 5–7.

Petitioners point to language in the Holmstead Memo that

they view as evidence of its binding character vis-à-vis the

states: “A demonstration supporting the designation of

20

boundaries that are less than the full metropolitan area must

show both that violations are not occurring in the excluded

portions of the metropolitan area and that the excluded

portions are not source areas that contribute to the observed

violations.” Id. at 7. But this language does not create a new

burden on the states; it merely reiterates the statutory

requirements. See § 7407(d)(1)(A)(i) (requiring Governors to

designate as nonattainment “any area that does not meet (or

that contributes to ambient air quality in a nearby area that

does not meet)” the NAAQS).

Nor does the Holmstead Memo bind EPA. The Memo

announces the C/MSA presumption as a rebuttable

presumption, which preserves the agency’s discretion to

deviate from the boundaries of a C/MSA in the final

designations. See Panhandle Producers & Royalty Owners

Ass’n v. Econ. Regulatory Admin., 822 F.2d 1105, 1110 (D.C.

Cir. 1987) (“‘An agency pronouncement is not deemed a

binding regulation merely because it may have some

substantive impact, as long as it leave[s] the administrator free

to exercise his informed discretion.’ . . . Presumptions, so

long as rebuttable, leave such freedom.” (quoting Brock v.

Cathedral Bluffs Shale Oil Co., 796 F.2d 533, 537 (D.C. Cir.

1986) (internal quotation marks omitted))).

Further, EPA has not applied the Holmstead Memo in a

binding manner. Petitioners again cite General Electric for

the proposition that an agency document will be considered

binding if “the affected private parties are reasonably led to

believe that failure to conform will bring adverse

consequences.” Gen. Elec., 290 F.3d at 383 (quoting

Anthony, supra, at 1328). The Memo “encouraged” states to

address all nine factors EPA identified, but did not require

them to do so. Holmstead Memo Guidance at 7. Some states

did not address all or even any of the factors. See, e.g., Letter

21

from Robert G. Burnley, Dep’t of Envtl. Quality,

Commonwealth of Virginia, to Donald S. Welsh, U.S. EPA

Region III (Feb. 13, 2004) (recommending that all of Virginia

be designated attainment without addressing any of the nine

factors); Letter from Stephanie R. Timmermeyer, West

Virginia Dep’t of Envtl. Prot., to Donald S. Welsh, U.S.

EPA Region III (Feb. 13, 2004) (recommending PM2.5

nonattainment areas to match the existing ozone

nonattainment areas without addressing any of EPA’s other

eight factors). EPA considered such submissions and did not

impose “adverse consequences,” notwithstanding the states’

failure to address the factors listed in the Holmstead Memo.

Compare State of West Virginia PM2.5 Designations—

Preliminary Recommendations, with PM2.5 Designations Rule,

70 Fed. Reg. at 1014–15 (showing that EPA designated as

attainment an area that West Virginia had proposed be

designated nonattainment, despite the fact that West Virginia

did not address eight of EPA’s nine factors).

In sum, we deny petitioners’ procedural claims because

EPA was not required to submit either the final designations

rule or the Holmstead Memo for notice and comment.

IV.

Petitioners next claim that EPA violated section 107(d) of

the Clean Air Act by applying the C/MSA presumption and

nine-factor test to identify areas that contribute to nearby

PM2.5 violations. As we explained above, we review EPA’s

interpretation of the Clean Air Act under Chevron, asking

whether Congress has “directly spoken to the precise

question at issue,” 467 U.S. at 842, and if so, whether

it has unambiguously foreclosed the agency’s statutory

interpretation, e.g., Sierra Club v. EPA, 536 F.3d 673, 677

(D.C. Cir. 2008). But if the statute is either silent or

22

ambiguous on the specific question at issue, we defer to

EPA’s statutory interpretation so long as it is reasonable. Id.

At the outset we observe that section 107(d) is replete

with the kinds of words that suggest a congressional intent to

leave unanswered questions to an agency’s discretion and

expertise, see Nat’l Cable & Telecomms. Ass’n v. Brand X

Internet Servs., 545 U.S. 967, 980 (2005) (statutory ambiguity

is delegation to the agency “to fill the statutory gap in

reasonable fashion”). Section 107(d) requires EPA to

designate an area as nonattainment if it “contributes to

ambient air quality in a nearby area” that exceeds the relevant

standard, § 7407(d)(1)(A)(i), yet the statute defines neither

“contributes” nor “nearby”—words that we have expressly

found ambiguous as used in other sections of the Act. See

Envtl. Def. Fund v. EPA, 82 F.3d 451, 459 (D.C. Cir. 1996)

(“contributes to” ambiguous in another section of the Clean

Air Act); Sierra Club v. EPA, 719 F.2d 436, 443–44 (D.C.

Cir. 1983) (same, as to “nearby”). It authorizes EPA

to revise state-submitted designations whenever it “deems”

such modifications “necessary,” yet it says nothing of

what precisely will render a modification “necessary.”

§ 7407(d)(1)(B)(ii). And section 107(d) requires states to

submit PM2.5 designations “based on air quality monitoring

data collected in accordance with any applicable Federal

reference methods,” § 7407(d)(6)(A), yet it fails to define

“based on” and “[t]here is no question that the phrase ‘based

on’ is ambiguous,” Sierra Club v. EPA, 356 F.3d 296, 305–06

(D.C. Cir. 2004); accord. Nuclear Energy Inst., Inc. v. EPA,

373 F.3d 1251, 1269 (D.C. Cir. 2004). “[A]mbiguities in

statutes within an agency’s jurisdiction to administer are

delegations of authority to the agency to fill the statutory gap

in reasonable fashion.” Brand X, 545 U.S. at 980. Because it

conveys no clear-cut approach for determining whether an

23

area contributes to a nearby PM2.5 violation, section 107(d)’s

text is consistent with such a delegation.

To be sure, a statute may foreclose an agency’s preferred

interpretation despite such textual ambiguities if its structure,

legislative history, or purpose makes clear what its text leaves

opaque. Cf. Ariz. Pub. Serv. Co. v. EPA, 211 F.3d 1280,

1287 (D.C. Cir. 2000) (court must “exhaust[] traditional tools

of statutory construction” at Chevron step one).

Notwithstanding petitioners’ torrent of arguments to the

contrary, this is not such a case—indeed, it isn’t even close.

We start with the argument that petitioners judge to be

their best. See Oral Arg. at 1:16–3:00. Pointing to section

107(d)(4), petitioners insist that the statute’s express mandate

that EPA apply the C/MSA presumption in other contexts

conclusively proves that Congress intended to preclude its use

here. Enacted as part of the 1990 Amendments to the Clean

Air Act, section 107(d)(4) “revise[s] . . . by operation of law”

the boundaries of certain urban ozone or carbon monoxide

nonattainment areas “to include the entire metropolitan

statistical or consolidated metropolitan statistical area,” unless

EPA determined that some portions “do not contribute

significantly to the violation of the national ambient air

quality standard.” § 7407(d)(4)(A)(iv)–(v). In contrast,

section 107(d)(6) says nothing about the C/MSA presumption.

Instead it provides that the PM2.5 area designations must be

“based on air quality monitoring data” and promulgated in

accordance with section 107(d)(1)’s general provisions for

area designations. § 7407(d)(6)(A). Citing the familiar canon

of statutory interpretation that “[w]here Congress includes

particular language in one section of a statute but omits it

from another section of the same Act, it is generally presumed

that Congress acts intentionally and purposely in the disparate

inclusion or exclusion,” Russello v. United States, 464 U.S.

24

16, 23 (1983) (internal quotation marks and brackets omitted),

petitioners insist that the statute’s exclusive inclusion of the

C/MSA presumption for the ozone and carbon monoxide

designations demonstrates Congress’ unambiguous intent to

preclude EPA from adopting the presumption here.

Although petitioners are correct that we construe statutes

to give meaning to the disparate inclusion of particular

language, that principle hardly compels the interpretation they

favor. When interpreting statutes that govern agency action,

we have consistently recognized that a congressional mandate

in one section and silence in another often “suggests not a

prohibition but simply a decision not to mandate any solution

in the second context, i.e., to leave the question to agency

discretion.” Cheney R. Co. v. ICC, 902 F.2d 66, 69 (D.C. Cir.

1990); see also Clinchfield Coal Co. v. Fed. Mine Safety &

Health Review Comm’n, 895 F.2d 773, 779 (D.C. Cir. 1990)

(“[W]here an agency is empowered to administer the statute,

Congress may have meant that in the second context the

choice should be up to the agency.”). Silence, in other words,

may signal permission rather than proscription. For that

reason, that Congress spoke in one place but remained silent

in another, as it did here, “rarely if ever” suffices for the

“direct answer” that Chevron step one requires. Cheney, 902

F.2d at 69 (internal quotation marks omitted); see also Am.

Forest & Paper Ass’n v. FERC, 550 F.3d 1179, 1181 (D.C.

Cir. 2008) (statute’s discrepant inclusion of the modifier

“competitive” to describe “markets” renders statutory

provision lacking the modifier ambiguous).

Undaunted, petitioners insist that the silence here is

unambiguously prohibitive. They point out that Congress not

only refused to treat PM2.5 like ozone and carbon monoxide

but chose an altogether different scheme in subsection

(d)(6)—one “based on air quality monitoring data,”

25

§ 7407(d)(6)(A), rather than OMB-drawn metropolitan

boundaries and a multi-factor test. As indicated above,

however, Congress’s mere choice of different standards in

subsections (d)(4) and (d)(6) tells us nothing about whether

Congress wanted to mandate different approaches or to permit

them. Thus, for this argument to succeed, subsection (d)(6)

must itself preclude EPA from adopting a test for PM2.5 like

the one that Congress mandated for ozone and carbon

monoxide in subsection (d)(4). But nothing in subsection

(d)(6) even hints at such a prohibition. Subsection (d)(6)(A)

requires states to submit PM2.5 designations “based on air

quality monitoring data collected in accordance with any

applicable Federal Reference methods”; subsection (d)(6)(B)

in turn requires EPA to promulgate those designations in

accordance with subsection (d)(1)’s general provisions. For

the sake of argument, we shall assume that subsection (d)(6)’s

“based on” language unambiguously applies to EPA even

though it appears only in the particular provision governing

states. We shall also assume that the language substantively

constrains EPA’s discretion in determining nonattainment

boundaries. But even given these assumptions, binding

precedent, the statute’s purpose, and basic common sense

foreclose petitioners’ argument that section 107(d)(6) itself

precludes EPA from adopting the C/MSA presumption and

nine-factor test.

First, as noted above, we have repeatedly held that the

words “based on” are unquestionably ambiguous: they neither

compel the agency to rest its decisions “solely on” the

specified factor nor indicate the extent to which the agency

may rely on additional factors. Sierra Club, 356 F.3d at 305–

06; accord. Nuclear Energy Inst., 373 F.3d at 1269. Instead,

they simply constrain the agency from “abandon[ing]” or

“supplant[ing]” the specified factor altogether. Sierra Club,

356 F.3d at 306. We need ask only whether EPA’s PM2.5

26

designations “can still reasonably be described as ‘based on’”

air quality monitoring data, id., and we have no doubt that the

contribution designations meet this modest standard. If

nothing else, the contribution designations are “based on” the

air quality monitoring data that demonstrate a nearby

violation of the NAAQS. Even were this insufficient, EPA’s

use of air quality monitoring data as part of its nine-factor

analysis—for instance, its use of urban excess and weighted

emissions scores based on speciation data—would surely

suffice.

Second, because subsection d(1) directs EPA to designate

some areas as nonattainment despite monitoring data that

provides no basis, on its own, to do so, see § 7407(d)(1)(A)(i),

we think it quite clear that the statute contemplates reliance on

factors other than monitoring data to determine contribution.

How could EPA possibly fulfill its statutory duty to

determine, for instance, whether emissions in Indiana

contribute to monitored violations in Chicago without

considering wind and emissions data from Indiana?

Obviously it couldn’t. That the statute fails to set forth the

additional criteria for EPA to consider in evaluating

contribution hardly forecloses EPA from developing such

criteria in order to accomplish Congress’s objectives. See

e.g., Entergy Corp. v. Riverkeeper, Inc., 129 S. Ct. 1498, 1508

(2009). Indeed, when a statute is “silent . . . with respect to

all potentially relevant factors, it is eminently reasonable to

conclude that [the] silence is meant to convey nothing more

than a refusal to tie the agency’s hands.” Id. (emphasis

added).

Still undaunted, petitioners advert to section 107(d)(3)—

which permits EPA to require a revision to an area

designation “on the basis of air quality data, planning and

control considerations, or any other air quality-related

27

considerations the Administrator deems appropriate,”

§ 7407(d)(3)—as evidence that Congress “knew how to

authorize a flexible, ‘multi-factor’ approach to attainment

decisions when it so intended.” Counties’ Opening Br. 20.

But the Supreme Court rejected just this kind of argument in

Entergy Corp. v. Riverkeeper, Inc., which asked whether EPA

may engage in cost-benefit analysis under section 316(b) of

the Clean Water Act given that it says nothing of cost-benefit

analysis while other sections expressly authorize it. 129 S.

Ct. at 1508. Pointing out that section 316(b) “is silent not

only with respect to cost-benefit analysis but with respect to

all potentially relevant factors,” the Court rejected the claim

that the silence reflected a prohibition, for if it did, “then the

EPA could not consider any factors in implementing [section

316(b)]—an obvious logical impossibility.” Id. Here we face

just this kind of overwhelming statutory silence. Although

logic dictates that EPA must evaluate some factors in addition

to monitoring data to determine contribution, the statute says

nothing about which factors it should consider. We thus

have no difficulty rejecting the claim that the statute

unambiguously forecloses EPA from adopting the C/MSA

presumption or considering its nine factors in applying it.

The legislative history petitioners cite fails to rehabilitate

their claim that section 107(d)(6) unambiguously requires

EPA to base all PM2.5 designations—including nonattainment

designations for contribution—“on air quality monitoring

data” alone. Although petitioners are correct that in the

Transportation Equity Act for the 21st Century, Congress

provided for the deployment of a PM2.5 monitoring network to

produce adequate monitoring data for these designations, that

does nothing to dispel the ambiguity over what criteria EPA

should rely on to assess contribution. Indeed, the particular

provision of TEA-21 that petitioners emphasize actually

reinforces that ambiguity rather than resolves it. See TEA-21

28

§ 6102(c)(1) (“Only data from the monitoring network . . .

shall be considered for such designations. Nothing in the

previous sentence shall be construed as affecting . . . the

Administrator’s authority to promulgate the designation of an

area as nonattainment, under section 107(d)(1) of the Clean

Air Act, based on its contribution to ambient air quality in a

nearby nonattainment area.”).

In sum, we conclude that neither section 107(d)’s

requirement that PM2.5 designations be “based on air quality

monitoring data” nor its mandate that EPA apply the C/MSA

presumption and a multi-factor test for pollutants other than

PM2.5 unambiguously reveals Congress’s intent to prevent

EPA from using the presumption and the nine-factor test to

determine contribution here. Our rejection of petitioners’

purportedly strongest argument is a fair harbinger of the fate

of their remaining statutory complaints.

To begin with, petitioners waived two of their statutory

arguments by failing to raise them in their opening briefs. See

New York v. EPA, 413 F.3d 3, 20 (D.C. Cir. 2005) (petitioners

waive those arguments that they fail to raise in their opening

briefs). Specifically, not until their reply briefs did they

present a statutory challenge to EPA’s interpretation that a

“nearby” area under section 107(d)(1)(A) may include non-

contiguous areas, or to its conclusion that an area’s future

reductions in emissions qualifies as a relevant factor for

assessing contribution. This leaves just two general

challenges: petitioners’ claim that the C/MSA presumption

and the nine-factor test run afoul of the statutory term

“contribute”; and their claim that the presumption

impermissibly encroaches on states’ statutory prerogative to

have first-say on area designations within their borders.

29

As to the textual claim, petitioners insist that the verb

“contribute” necessarily connotes a significant causal

relationship, meaning that EPA may not designate a county as

contributing to nonattainment if “corrective measures in [the

county] will do nothing to address the problem or help

achieve compliance in the nonattainment area.” Counties’

Opening Br. 25. We reject both the major and the minor

premise. Although petitioners cite one dictionary that

supports the claim that the adverb “significantly” is implicit in

the verb “contribute,” EPA cites other dictionaries that define

“contribute” without reference to any threshold level of

significance. This alone suggests an ambiguity that fatally

undermines petitioners’ Chevron step one argument. See

Cellular Telecomms. & Internet Ass’n v. FCC, 330 F.3d 502,

509 (D.C. Cir. 2003) (“[D]ueling over dictionary definitions

is pointless, for it fails to produce any plain meaning of the

disputed word.”). But even were we to think that “contribute”

unambiguously means “significantly contribute,” we still

disagree that “significantly contribute” unambiguously means

“strictly cause.” Cf. Michigan v. EPA, 213 F.3d 663, 667–68

(D.C. Cir. 2000) (“significant” is ambiguous). Given that the

statute uses the word “contribute” and that a contribution may

simply exacerbate a problem rather than cause it, we see no

reason why the statute precludes EPA from determining that a

county’s addition of PM2.5 into the atmosphere is significant

even though a nearby county’s nonattainment problem would

still persist in its absence. In fact, a contrary interpretation of

“contribute” would effectively preclude a nonattainment

designation for any attaining county when the cause of the

violation is metropolitan-wide. We may not interpret

“contribute” in a way that does such violence to section

107(d)’s very purpose.

We also reject petitioners’ argument that EPA violated

the statute by failing to articulate a quantified amount of

30

contribution that would trigger a nonattainment designation.

Petitioners apparently prefer a bright-line, “objective” test of

contribution, see, e.g., Counties’ Opening Br. 28, but it is the

statute, not petitioners’ preferences, that constrains EPA’s

discretion. And nothing in the statute compels EPA to

quantify a uniform amount of contribution below which

counties will automatically escape nonattainment designations

or to quantify similar thresholds for the nine factors EPA

evaluated in making those determinations. Section 107(d) is

ambiguous as to how EPA should measure contribution and

what degree of contribution is sufficient to deem an area

nonattainment, as even petitioners seem to concede, see

Counties’ Reply Br. 13 (“EPA was supposed to be defining

and deciding ‘contributes.’”). Thus, reasonably exercising the

discretion that Congress delegated to it, EPA interpreted

“contribute” to mean “sufficiently contribute,” and then

applied the C/MSA presumption and nine-factor test precisely

to identify those areas that meet that definition. Petitioners

offer no plausible reason to think that the statute forecloses

this approach.

Nor do we agree with petitioners that EPA’s failure to

quantify its analysis somehow rendered its interpretation of

“contribute” arbitrary and capricious and therefore

unreasonable under Chevron step two. Cf. Northpoint Tech.,

Ltd. v. FCC, 412 F.3d 145, 151 (D.C. Cir. 2005) (statutory

interpretation that is arbitrary and capricious is unreasonable

under Chevron step two). An agency is free to adopt a

totality-of-the-circumstances test to implement a statute that

confers broad discretionary authority, even if that test lacks a

definite “threshold” or “clear line of demarcation to define an

open-ended term.” PDK Labs., Inc. v. DEA, 438 F.3d 1184,

1195 (D.C. Cir. 2006) (internal quotation marks omitted). To

be reasonable, such an “all-things-considered standard” must

simply define and explain the criteria the agency is applying,

31

id. at 1194, something the Holmstead Memo and certainly the

Technical Support Document did in spades. Of course, EPA

may have applied its nine-factor test inconsistently, resulting

in similar counties being treated dissimilarly—a question we

address in Part V. EPA may also have applied it so

erroneously in a particular case that it could not have

reasonably concluded that a county was contributing to

nearby violations—an issue we consider in Part VI. But

EPA’s use of a flexible multi-factor analysis is not in and of

itself unreasonable just because it lacks quantitative standards.

See id. at 1194–95.

We are equally unimpressed by petitioners’ last general

argument: that the C/MSA presumption unlawfully “deprived

states of the deference to which their designations were

entitled” under section 107(d). States’ Opening Br. 1. To the

extent petitioners are claiming that EPA owes the states a

measure of procedural deference under section 107(d),

we agree that EPA must wait its turn before it makes any

individual county designations. Indeed, in contrast to its

many ambiguities, section 107(d)(1) clearly provides

that states submit their “initial designations” first,

§ 7407(d)(1)(A), and only then does EPA promulgate or

modify the designations as it “deems necessary,”

§ 7407(d)(1)(B)(ii). Not only is that precisely what happened

here, but nothing in section 107(d)(1) prevents EPA from

developing general principles to govern its exercise of

discretion when the time comes, or from announcing those

general principles before the states submit their initial

designations. To the extent petitioners think that EPA owes

the states a measure of substantive deference under section

107(d)(1)—a claim that seems implicit in their objection that

the C/MSA presumption somehow alters states’ “burden” in

the designation process, see States’ Opening Br. 24—we

disagree. Though EPA may, of course, go along with states’

32

initial designations, it has no obligation to give any quantum

of deference to a designation that it “deems necessary” to

change. See, e.g., Pa. Dep’t of Envtl. Prot. v. EPA, 429 F.3d

1125, 1129 (D.C. Cir. 2005) (recognizing that section 107(d)

gives “deference” to states’ initial designations provided EPA

deems no modification necessary). In short, EPA had

authority to apply the C/MSA presumption at the time it

rejected the states’ submissions. We see no reason why

section 107(d)(1) would force EPA to bite its tongue until

then.

Having rejected petitioners’ arguments that section

107(d) unambiguously precludes EPA from adopting the

C/MSA presumption and nine-factor test, we can easily

conclude that EPA reasonably interpreted the statute as

permitting it to do so. Even if we read section 107(d)

favorably to petitioners, it requires only that EPA designate,

based on air quality monitoring data, nonattainment areas that

either violate or contribute to violations of the PM2.5 NAAQS.

Acting on evidence that urban PM2.5 violations usually stem

from metropolitan-wide activities, EPA adopted a

presumption that designates all metropolitan areas as

nonattainment when at least one metropolitan area registers a

PM2.5 violation, as well as a specifically defined multi-factor

analysis to assess when that presumption fails to reflect the

realities of a given metropolitan area. Petitioners give us

every reason to think they would prefer another system of

analysis—specifically, one that would allow them to escape

certain nonattainment designations—but they give us no

reason to think the system EPA selected is unreasonable.

V.

Petitioners next argue that the Designations Rule is

arbitrary and capricious because it is riddled with

methodological flaws and inconsistencies. They challenge the

33

Rule in four regards: EPA’s designation of noncontiguous

townships as nonattainment, the agency’s refusal to account

for some potential emissions reductions, the so-called carbon

error in some weighted emissions scores, and the way EPA

applied the nine-factor test.

“[W]e apply the same standard of review under the Clean

Air Act as we do under the Administrative Procedure Act

(APA), 5 U.S.C. § 706(2)(A),” Allied Local & Reg’l Mfrs.

Caucus v. EPA, 215 F.3d 61, 68 (D.C. Cir. 2000), and will set

aside the Designations Rule only if it is “arbitrary, capricious,

an abuse of discretion, or otherwise not in accordance with

law,” § 7607(d)(9)(A). We must affirm the Rule if the record

shows EPA considered all relevant factors and articulated a

“rational connection between the facts found and the choice

made.” Burlington Truck Lines v. United States, 371 U.S.

156, 168 (1962). Of particular note in this challenge, we give

an “extreme degree of deference to [EPA] when it is

evaluating scientific data within its technical expertise,” City

of Waukesha v. EPA, 320 F.3d 228, 247 (D.C. Cir. 2003)

(internal quotation marks omitted). Such deference is

especially appropriate in our review of EPA’s administration

of the complicated provisions of the Clean Air Act. See Nat’l

Ass’n of Clean Air Agencies v. EPA, 489 F.3d 1221, 1229

(D.C. Cir. 2007).

In basing its designation decisions on a rigorous analysis

of each county’s particular attributes, EPA satisfied the

requirements of reasoned decisionmaking. Given our highly

deferential standard of review, these four challenges provide

no basis to question EPA’s general analysis or to upset the

entire Designations Rule.

34

A. Designation of Noncontiguous Townships

As we have described above, EPA’s designation analysis

starts with two presumptions. See supra at 12–13. First, “if a

PM2.5 monitor [is] violating” the NAAQS, “at a minimum

[EPA will] designate the entire county where that monitor is

located as nonattainment” because the “county boundary” is

“the basic jurisdictional boundary for determining the extent

of the area reflected by the PM2.5 monitor.” PM2.5

Designations Rule, 70 Fed. Reg. at 946–47. Second, all

counties within the C/MSA contribute to that violation. See

id. at 947; Holmstead Memo Guidance at 4. When these

presumptions operate in tandem, a violating monitor within a

C/MSA will result in a single contiguous block of

nonattainment counties that includes both the county with the

violating monitor and the other C/MSA counties that are

deemed to contribute to that violation. Likewise, when EPA

includes out-of-C/MSA counties in a nonattainment block,

those counties typically adjoin violating counties. But EPA

also invites states to recommend smaller PM2.5 designation

areas on a “case-by-case basis” if they “provide an adequate

justification demonstrating that a smaller area would include

the full area that is violating the standards and all nearby

source areas that contribute to the violation.” Holmstead

Memo Guidance at 6. Some states took up EPA’s offer and

asked that a township rather than a county be designated as

nonattainment when a power plant in the township was the

overwhelming source of the county’s contribution to a nearby

PM2.5 violation. See PM2.5 Designations Rule, 70 Fed. Reg. at

947; Technical Support Document § 6.5.4.4 (Discussion).

To borrow petitioners’ imagery, this approach created an

island of nonattainment—the township—surrounded by a sea

of attainment throughout the remainder of the county.

Industry petitioners argue that creating such islands of

nonattainment arbitrarily deviates from the presumption that

35

designations should be made at the county level. Because

emissions from a power plant in a township do not skip over

all other parts of the surrounding county and come to rest in a

nearby area with a violating monitor, petitioners argue that

violating areas designated nonattainment should be

contiguous to those areas contributing to the violation.

We find no fault in EPA’s conclusion that it would be

unreasonable to designate as nonattainment those areas that

do not, in fact, contribute to violations. EPA designated as

nonattainment a township with an emitting source—rather

than the entire county—because “it would be inappropriate to

include other portions of a county, merely because those

portions lay between the large stationary source and the

remainder of the designated nonattainment area.” PM2.5

Designations Rule, 70 Fed. Reg. at 947. Although contiguity

of nonattainment areas may follow from the operation of the

Rule’s twin presumptions, the designations process does not

mandate that result when the scientific data show that a source

contributing to a violation is not in an area contiguous to the

county with the violating monitor. According to the

Technical Support Document, EPA designated townships

rather than entire counties as nonattainment only when a

power plant in the township was responsible for the vast

majority of the county’s PM2.5 emissions. For example, the

Conesville Plant in Franklin Township emitted 99% of the

SO2, 90% of the NOx, 78% of the carbon, and 87% of the

crustal emissions for all of Coshocton County. See Technical

Support Document § 6.5.4.4 (Factor 1). By designating only

Franklin Township as nonattainment, EPA accounted for the

lion’s share of Coshocton County’s emissions that “are

contributing to the violation in the Columbus Metropolitan

Area,” id. (Discussion). EPA presented comparable statistics

for the townships designated nonattainment in Adams and

Gallia Counties. Id. § 6.5.4.6 (Factor 1) (providing a similar

36

rationale for designating Monroe and Sprigg Townships in

Adams County and Cheshire Township in Gallia County).

EPA reasonably concluded there was no need to designate as

nonattainment any other part of these counties.

Industry petitioners also argue that EPA failed to use

monitoring or modeling data in designating townships as

nonattainment. But petitioners fail to identify any township

designations lacking such support. And although we have no

obligation to comb through the voluminous record in this case

to determine the merits of an argument for which petitioners

offer no support, see FED. R. APP. P. 28(a)(9)(A) (requiring

briefs to contain “citations to the authorities and parts of the

record on which the appellant relies”), we note at least one

instance in which we easily found that the record contradicts

their assertion. EPA used air quality modeling to determine

that the power plant in Franklin Township was responsible for

the vast majority of Coshocton County’s contribution to PM2.5

violations in the Columbus Metropolitan Area. See

Memorandum from Brian Timin & Richard Damberg, EPA

Office of Air Quality Planning & Standards, Air Quality

Modeling To Assess Power Plant Impacts 2 (Jan. 20, 2006);

Technical Support Document § 6.5.4.4 (Discussion, Factor 1,

Factor 2); see also PM2.5 Designations Rule, 70 Fed. Reg. at

947 (explaining that EPA uses speciation data from monitors

to determine which sources contribute to violations).

Finally, industry petitioners contend that because EPA

designated only contiguous areas as nonattainment for

excessive levels of ozone, it acted arbitrarily in not doing so

for PM2.5. But ozone was the subject of a different

designations process and a separate rulemaking, and nothing

compels EPA to use the same approach for PM2.5. Petitioners

emphasize that PM2.5 and ozone are both pollutants that can

travel long distances. That similarity alone, however, is not

37

enough to force EPA to treat the two pollutants as if they pose

the same threat to public health and welfare. When EPA set

forth the criteria it would use during the PM2.5 designations

process, it explained that “unlike ozone,” PM2.5 “can arise on

a very localized basis. For example, violations can be caused

by the emissions from a single major source or set of

sources.” Holmstead Memo Guidance at 6. Given this

critical difference, EPA was well within its discretion to

consider state recommendations for smaller PM2.5

designations on a “case-by-case basis,” id.

B. Future Reductions in Emissions

When it is evident that federally enforceable pollution

controls will yield significant near-term reductions in

emissions, EPA accounts for those forecasted reductions in

estimating an area’s emissions levels for the purpose of

evaluating contribution. See Letter from Stephen L. Johnson,

Adm’r, EPA, to David M. Flannery, Counsel For Midwest

Ozone Group et al., Attach. at 13 (Aug. 16, 2007) (“Johnson

Attach.”). Industry petitioners argue that EPA overestimated

emissions levels and thus made mistaken designations by

failing to account for future reductions from two federal

programs: the Clean Air Interstate Rule (CAIR) and the NOx

State Implementation Plan (also known as the “NOx SIP

Call”). See generally North Carolina v. EPA, 531 F.3d 896,

902–03 (D.C. Cir.) (describing programs), modified, 550 F.3d

1176 (D.C. Cir. 2008). We find no error in EPA’s refusal to

consider estimates of lower emissions levels that might result

from these two programs.

EPA promulgated CAIR to reduce SO2 and NOx

emissions from upwind sources in 28 states and the District of

Columbia that contribute to nonattainment levels for ozone

and PM2.5 in downwind states. Id. at 903. When EPA made

its PM2.5 designations, it reasonably decided emissions

38

reductions from CAIR were, at the time, uncertain and should

not be a factor in estimating emissions levels for the

designations process. See Johnson Attach. at 13 (explaining

that EPA would include projected emissions reductions only

for federally enforceable agreements that were “in place by

the time that EPA was required to promulgate the

designations in December 2004”). As discussed above,

designations for C/MSAs, counties, and townships turn in part

on contributions from identifiable sources. When EPA made

its designation decisions in December 2004, there was no

assurance that a state’s compliance with CAIR, which did not

become effective until March 2005, would result in reduced

PM2.5 emissions for specific sources. Indeed, CAIR did not

require states to submit to EPA their recommendations as to

which power plants would reduce SO2 and NOx emissions and

how they would do so until September 2006—nearly two

years after the agency had designated areas under the PM2.5

NAAQS. See Rule To Reduce Interstate Transport of Fine

Particulate Matter and Ozone (Clean Air Interstate Rule), 70

Fed. Reg. 25,162, 25,162 (May 12, 2005); Rule To Reduce

Interstate Transport of Fine Particulate Matter and Ozone

(Clean Air Interstate Rule): Reconsideration, 71 Fed. Reg.

25,304, 25,305 (Apr. 28, 2006) (“Each State covered by

CAIR may independently determine which emission sources

to control, and which control measures to adopt.”). Even

EPA’s provisional compliance regime—designed to start

reductions in emissions levels before states were required to

file their plans—did not take effect until more than a year

after the agency had completed designating areas. See

Rulemaking on Section 126 Petition from North Carolina To

Reduce Interstate Transport of Fine Particulate Matter and

Ozone, 71 Fed. Reg. 25,328, 25,328 (Apr. 28, 2006); see also

North Carolina, 531 F.3d at 903 (describing program). It was

therefore reasonable for EPA to disregard as too speculative

any claimed emissions reductions that might come from

39

CAIR when it promulgated the PM2.5 designations in

December 2004. See Johnson Attach. at 8 n.11.

It was likewise reasonable for EPA to disregard

forecasted reductions from the NOx SIP Call. Created to

reduce ozone pollution, this program requires 22 upwind

states and the District of Columbia to decrease NOx

emissions, a significant precursor to PM2.5, but it has nothing

to do with reducing SO2, another significant PM2.5 precursor.

See Finding of Significant Contribution and Rulemaking for

Certain States in the Ozone Transport Assessment Group

Region for Purposes of Reducing Regional Transport of

Ozone, 63 Fed. Reg. 57,356, 57,356 (Oct. 27, 1998). The

power plants in question are often among the largest sources

of SO2 in their respective areas. See Johnson Attach. at 8.

EPA concluded that reducing NOx but not SO2 was a step in

the right direction for reducing PM2.5, but it fell short of what

EPA required to consider forecasted reductions in its

designations. See id. at 14. Lacking evidence of significant

near-term reductions in SO2, EPA reasonably decided not to

alter nonattainment designations based only on forecasted

reductions in NOx. See, e.g., Technical Support Document

§ 6.4.4.1 (Factor 9) (showing EPA designated as attainment

Stokes County, North Carolina, because a power plant there

installed controls certain to reduce significantly both NOx and

SO2).

C. Carbon Error

In making nonattainment designations, EPA relied upon a

mistaken estimate of carbon emissions by power plants that

burn bituminous coal. Industry petitioners seize on this error

as evidence that the Designations Rule is arbitrary and

capricious. We disagree. EPA used the best available

information, and the mistaken estimate of carbon had no

effect on the reasonableness of the challenged designations.

40

Among the analytical tools EPA uses to make

designation determinations is a county’s weighted emissions

score, which allows the agency to compare SO2, NOx, carbon,

and crustal emissions across counties within a C/MSA. See

PM2.5 Designations Rule, 70 Fed. Reg. at 947. This score is

not based on measurements of actual emissions by a particular

source. Instead, EPA uses emissions estimates from the

National Emissions Inventory (NEI) to calculate total PM2.5

emissions, as well as SO2, NOx, carbon, and crustal emissions

for each county. See What Is the National Emissions

Inventory (NEI)?, http://www.epa.gov/ttn/chief/net/neiwhatis.

html (last visited June 11, 2009). The NEI is a database

assembled by EPA’s Emission Inventory and Analysis Group

that houses estimates of the kinds and amounts of substances

emitted by particular sources, including point sources like

power plants and mobile sources like automobiles. Based on

these estimates, EPA creates “speciation profiles,” which

describe the chemicals that make up the emissions associated

with a particular type of source. See Speciation: Emissions

Modeling Clearinghouse, http://www.epa.gov/ttn/chief/emch/

speciation/ (last visited June 11, 2009).

The speciation profile EPA used for large electric

generating units (EGUs) estimated that carbon makes up 21%

of their PM2.5 emissions. As it turns out, that estimate was

wrong for plants that burn bituminous coal. Carbon accounts

for only 2.9% of their PM2.5 emissions. See J.A. at 2848–49.

EPA updated the speciation profile for these plants in its 2006

revision of the PM2.5 NAAQS, but retained the old profile for

plants that burn primarily lignite coal.

Industry petitioners argue that because the 2004

designations were based on a flawed EGU profile that vastly

overestimated carbon emissions, EPA’s nonattainment

designations for counties with large electric power plants that

41

burn bituminous coal—particularly the 23 identified in the

petition for reconsideration—are likewise flawed. EPA

responds that its ultimate designations did not turn on any one

estimate of a single chemical component of PM2.5. Rather,

the agency relied on numerous data points, including

emissions levels and county rankings of weighted emissions

scores within a C/MSA, that were largely unaffected by the

lower carbon estimate. According to EPA, changes in the

speciation profile for plants that burn bituminous coal did not

substantially lower total PM2.5 emissions estimates. Instead,

the proportions of pollutants emitted by these sources

changed. Specifically, the estimate of crustal particles, also a

precursor to PM2.5, increased as the carbon estimate

decreased. See Johnson Attach. at 4.

We hold that EPA was not obligated to upend the

designations process when it discovered a mistake in its

speciation profile for certain power plants. EPA used the best

information available in making its designations, and that is

all our precedent requires. In American Iron & Steel Institute

v. EPA, 115 F.3d 979, 1006 (D.C. Cir. 1991), the petitioners

argued that EPA’s estimate for the mercury concentration

permitted in the Great Lakes was flawed because the agency

used inaccurate data that had since been corrected. Relying

on ICC v. Jersey City, 322 U.S. 503 (1944), and Vermont

Yankee Nuclear Power Corp v. Natural Resources Defense

Council, 435 U.S. 519 (1978), we held that EPA did not act

arbitrarily by using the older data in its calculation. “The

agency was not obliged to stop the entire process because a

new piece of evidence emerged. If this were true then the

administrative process could never be completed. An agency

does, however, have an obligation to deal with newly

acquired evidence in some reasonable fashion.” Am. Iron,

115 F.3d at 1007.

42

Here, EPA dealt with newly acquired evidence in a

reasonable fashion by explaining why it would not have

changed the challenged designations. EPA is correct that

revisions to the speciation profile for plants that burn

bituminous coal altered only one component of the weighted

emissions score, which itself is only one of numerous

analytical tools used to assess the first of nine factors EPA

considers in determining contribution to PM2.5 violations.

Speciation profiles for power plants are by no means the

exclusive or even the primary basis for EPA’s designations,

but merely make up one part of a much larger and multi-

factored decisionmaking process. Johnson Attach. at 6–7.

Petitioners nonetheless contend that the carbon error is

particularly important because carbon typically makes up a

large portion of the urban excess and therefore weighs heavily

in these counties’ weighted emissions scores, which

themselves weigh heavily in the contribution analysis because

of the presence of large power plants. That may be so, but

EPA granted a March 2006 request to recalculate the

weighted emissions scores using the revised estimates and

concluded

that even if [the agency] were to reconsider the

designations, the area by area evaluation of

counties with emissions scores or activities

contributing to violations of the NAAQS

would not result in a different outcome. Of

the counties [petitioners] identified in

[their] petition, EPA sees no change in the

rank or magnitude of sources relative to

other counties in the areas that would negate

the appropriateness of inclusion of the

counties within their respective designated

nonattainment areas.

43

Letter from Stephen L. Johnson, Adm’r, EPA, to David M.

Flannery, Counsel For Midwest Ozone Group et al. 2–3 (Aug.

16, 2007); see also J.A. at 2881–83 (showing initial and

revised scores for the 23 counties identified by petitioners);

Johnson Attach. at 10–12 (explaining why particular

designations would not have changed with new data). Even

with a change in the estimated proportion of carbon emitted

by plants that burn bituminous coal, the overall level of

pollutants emitted by those EGUs generally stayed the same,

as did county rankings of weighted emissions scores. For

example, EPA explained that using the new speciation data

for a power plant in Jefferson County, Indiana, would not

have changed its nonattainment designation despite industry

petitioners’ claim that it is among the most problematic of

EPA’s determinations. See J.A. at 2826 (Midwest Ozone

Petition for Reconsideration). Although the weighted

emissions score for Jefferson County would have been lower,

it still would have been higher than surrounding counties’

scores because of the significant levels of SO2 and NOx that

the county’s power plant continued to emit. Johnson Attach.

at 12. EPA dealt with the so-called carbon error in a

reasonable fashion.

D. Application of the Nine-Factor Test

As explained above, EPA uses nine factors—including

things like air quality, population density, and traffic

patterns—to determine the boundaries of areas contributing to

nearby PM2.5 violations. See PM2.5 Designations Rule, 70

Fed. Reg. at 947; see also supra at 8. State petitioners argue

generally that EPA arbitrarily applied its nine-factor test by

treating similarly situated counties differently without

adequately explaining the allegedly divergent outcomes. In

each of their challenges, petitioners seize upon discrete data

points and ignore the very nature of the nine-factor test, which

44

is designed to analyze a wide variety of data on a “case-by-

case basis,” Holmstead Memo Guidance at 6. It is EPA’s

holistic assessment of numerous factors that drives the

process—no single factor determines a particular designation.

And although petitioners seek to paint a picture of system-

wide inconsistencies, their challenges really amount to an

attack on EPA’s designations of a small group of New York

counties. Although we address such individual challenges in

Part VI, we conclude here that with respect to the system as a

whole, EPA consistently applied its nine-factor test and

adequately explained its decisions based on record evidence.

1. First Factor:

EPA’s Characterizations of County Emissions

The first of the nine factors EPA uses to designate areas

calls for the agency to consider how emissions levels

contribute to nearby PM2.5 violations. In describing these

levels, EPA characterizes a county’s emissions as low, high,

significant, insignificant, and so forth. State petitioners argue

that EPA characterized county emissions inconsistently,

providing further evidence that the designations were

arbitrary. For example, petitioners claim it is manifestly

arbitrary to designate as attainment counties with emissions

levels EPA characterized as “low” based on weighted

emissions scores of 9.4 (Sevier County, Tennessee) and 6.3

(Jasper County, Georgia), while designating as nonattainment

counties with lower scores of 4.5 (Orange County, New

York), 3.7 (Westchester County, New York), and 1.9

(Rockland County, New York). States’ Opening Br. 34. As

explained above, a weighted emissions score reflects only a

county’s share of a C/MSA’s total emissions. Weighted

emissions scores cannot be used in any meaningful way to

compare emissions levels between counties in different

C/MSAs. Because cumulative emissions scores for all

45

counties within a C/MSA must total 100, areas with few

counties (like the Athens, Georgia, MSA) will invariably have

relatively larger county-level scores than areas with numerous

counties (like the NY-NJ-CT-PA C/MSA), even though

emissions levels in the smaller C/MSA may be lower.

Likewise, petitioners argue that two instances in which

EPA revised a county designation from nonattainment to

attainment show that its characterization of emissions data

and subsequent designations were arbitrary. EPA originally

described the emissions levels in Woodford County,

Kentucky, as “significant” and designated it as nonattainment.

Technical Support Document § 6.4.3.3 (Factor 1). But EPA

later concluded—without any change in emissions levels—

that the county “has relatively low emissions,” id.

(Justifications for Changes to EPA Recommendations

Contained in the June 24, 2004, Letters to States), and revised

its designation to attainment. These changes, petitioners

argue, reflect the flawed manner in which EPA applied the

first factor. But EPA adequately explained the change. After

the initial designation, Kentucky submitted evidence that

PM2.5 violations in nearby Fayette County were due to local

sources, not emissions from Woodford County as originally

thought. Id. Petitioners reply that EPA used the new data to

explain the change in Woodford County’s designation, not the

change in EPA’s assessment of emissions levels. To the

extent that is even true, though, we can reasonably discern

EPA’s path. Given that the weighted emissions score is a

rough estimate of a county’s relative (and relevant) emissions

in the first place, EPA simply interpreted the numeric score

differently when the new data suggested its facial significance

was inaccurate.

In the same vein, petitioners contend EPA acted

arbitrarily in revising its designation for Jasper County,

46

Georgia. Finding “significant emissions” that potentially

contribute to PM2.5 violations in other parts of the region,

EPA originally designated the county as nonattainment. See

id. § 6.4.2.2 (Factor 1). Data later submitted by Georgia,

however, showed that emissions from a source in Jasper

County were actually insignificant, prompting EPA to

redesignate the county as attainment. See id. § 6.4.2.1

(Justification for Changes to EPA Recommendations

Contained in the June 24, 2004, Letters to States); Letter from

Ron Methier, Chief, Air Prot. Branch, Ga. Dep’t of Natural

Res., to Beverly Bannister, Dir., Air, Pesticides & Toxics

Mgmt. Div., EPA Region 4, at 2 (Nov. 1, 2004). Far from

being arbitrary, these revised designations demonstrate the

reasonableness of EPA’s case-by-case approach to applying

the first factor.

2. First Factor:

EPA Region 1’s Use of a Bright-line Test

As explained in greater detail in Part VI, EPA Region 1

used a bright-line test to determine which counties within a

C/MSA would be designated as attainment. The test worked

like this: EPA Region 1 ranked each of its counties from

highest to lowest according to their weighted emissions

scores. Starting from the top of the list, EPA Region 1 added

each county’s score and stopped when the sum hit 80%.

Counties above the 80% cut-off point were presumed to be

nonattainment; those below were designated as attainment,

provided they did not have a violating monitor and were not

among those recommended for nonattainment status by a

state. See Technical Support Document § 6.1.1 (Factor 1).

State petitioners argue that application of this 80% test led to

inconsistent area designations, and they are right in one

instance. Rockland County, New York, which is not in EPA

Region 1 and was designated as nonattainment, would have

been designated as attainment under the 80% test. Such an

47

inconsistency is evidence of an arbitrary designation, but as

Part VI explains, EPA’s mistaken designation of Rockland

County is an aberration, and petitioners fail to identify any

other designation that might have changed had EPA applied

the 80% test elsewhere. Nothing about the way EPA Region

1 applied the first factor reveals a fundamental problem with

EPA’s evaluation of emissions in potentially contributing

areas.

3. Second Factor: Use of Design Values

Under the second of the nine factors, which looks to air

quality, EPA uses monitoring data to compute a “design

value” to describe the concentration of ambient PM2.5 in a

county. See supra at 12. The agency then compares the

design value to the annual NAAQS to help determine whether

the county is violating PM2.5 standards or contributing to

violations nearby. See id.; EPA Br. 14. State petitioners

argue that EPA arbitrarily designated some counties as

nonattainment despite their relatively low design values and

other counties as attainment despite their higher design

values. For example, EPA designated Hardin County,

Kentucky, as attainment even though its design value of 14.1

was higher than the 12.5 design value for Westchester

County, New York, which was designated as nonattainment.

See Technical Support Document § 6.4.3.2 (Factor 2); id.

§ 6.2.2 (Factor 2).

As EPA explained, however, design values alone do not

determine designations based on contribution. Indeed, they

are merely one component, albeit an important one, of a

complex process that ultimately yields designations.

Petitioners’ argument ignores the multiple factors EPA uses in

making case-by-case assessments of counties’ contributions to

nearby violations. See Holmstead Memo Guidance at 4.

Some areas, like Hardin County, may have relatively high

48

design values but still fall short of violating the annual PM2.5

standard of 15 micrograms per cubic meter. And many

such counties are not contributing areas because they

have low rankings for other factors like population,

traffic, and emissions levels. See, e.g., Technical Support

Document § 6.4.3.2 (explaining Hardin County’s attainment

designation). The three areas state petitioners use as

examples of inconsistent treatment—Nassau, Suffolk, and

Westchester Counties in New York—may have had lower

design values when compared to other attainment areas, but

each ranked high for emissions levels, population, and

number of commuters, all of which support the determination

that they contributed to nearby violations. See id. § 6.2.2. In

short, EPA had ample evidence upon which it based its

designation of these counties as nonattainment, despite their

relatively low design values.

4. Sixth and Seventh Factors:

Distance Between a Power Plant and a Violating Monitor

EPA takes account of the distance between a power plant

and a violating monitor to help determine whether an area’s

meteorological features (the sixth factor) and its particular

geography and topography (the seventh factor) will increase

the likelihood that emissions from the plant will contribute to

a violation. State petitioners argue that EPA used this

distance inconsistently. For example, the agency designated

Clearfield County, Pennsylvania, as attainment even though it

has a power plant 60 miles from a violating monitor. See id.

§ 6.3.4.2 (Discussion). By contrast, EPA designated Orange

County, New York, as nonattainment even though its power

plant is 50 miles from the closest violating monitor. See id.

§ 6.2.2. But EPA never placed the type of weight on the

distance factor that petitioners’ argument assumes. Although

EPA considered the distances, it weighed other factors as

well. For example, Orange County has very high emissions

49

levels, and meteorological data show winds blowing from the

county toward violating monitors elsewhere. See id.

Clearfield County, on the other hand, has mountainous terrain

and other geographic features limiting emissions travel.

See id. § 6.3.4.2 (Discussion). Petitioners claim that the

attainment designation for Jasper County, Georgia,

demonstrates inconsistency because it has a power plant 45

miles from the nearest violating monitor. But the plant’s

emissions are relatively insignificant, and other factors—such

as low population and few commuters—support the county’s

designation. See id. § 6.4.2.1 (Justification for Changes to

EPA Recommendations Contained in the June 24, 2004,

Letters to States); Letter from Ron Methier to Beverly

Bannister at 2. Once again, seizing upon a single factor

misapprehends the purpose of the nine-factor test.

5. Multiple Factors

Finally, petitioners compare weighted emissions scores,

design values, population density, number of commuters, and

population growth for four attainment counties (Lee County,

Alabama; Russell County, Alabama; Sevier County,

Tennessee; and Fulton County, Ohio) with the same data for

one nonattainment county—New York’s Orange County—to

illustrate that EPA applied the nine factors inconsistently,

rendering the designation process unpredictable and arbitrary.

See Technical Support Document §§ 6.4.2.5, 6.4.6.2, 6.5.4.9.

Although this argument acknowledges, where the others do

not, that EPA considers how the various factors might work

together, it fails for two reasons. First, as we have already

explained, see supra at 15, comparisons of weighted

emissions scores between counties in different C/MSAs are

meaningless. And second, even though Orange County

ranked relatively low on some factors, which might suggest it

was a good candidate for an attainment designation, it also

has emissions levels of PM2.5, SO2, and NOx that far exceed

50

the levels of the four attainment counties petitioners point to.

See Technical Support Document § 6.2.2. Orange County’s

designation, which is adequately justified, is yet another

illustration of the case-by-case analysis that the Designations

Rule calls for and the nine-factor test achieves.

VI.

Petitioners finally argue that even if the PM2.5

nonattainment designations are reasonable as a general matter,

certain individual county designations are independently

arbitrary and capricious. With but one exception, we reject

these challenges as well.

A. New York County Designations

New York challenges the nonattainment designations of

five counties surrounding New York City: Suffolk,

Westchester, Nassau, Orange, and Rockland—collectively the

“outer counties.” We find New York’s claims without merit,

except for its challenge to the designation of Rockland

County, which we remand to EPA for additional explanation.

New York makes several broad challenges to the

designations of the outer counties. Most generally, the state

argues that EPA’s designations lack a rational basis and that

EPA failed to respond to the comments New York submitted.

To justify the nonattainment designations for Westchester,

Suffolk, and Nassau Counties, EPA cites their high emissions,

population, traffic, and commuting patterns. For Orange

County, EPA relies on high emissions, as indicated by a

weighted emissions score ranking it fifth in the CMSA. EPA

also relies on meteorological data to show that wind blows

from each of the outer counties toward the violating monitors

some percentage of the time. Technical Support Document

at 6-24 to -36. EPA considered and responded in some

51

detail to New York’s comments challenging the designations.

Responses to Comments EPA Region 2 at 2-9 to -14. We

find that EPA’s basis for designating Suffolk, Westchester,

Nassau, and Orange Counties can reasonably be discerned

from the record. See Motor Vehicles Mfrs. Ass’n v. State

Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983) (“We

will . . . ‘uphold a decision of less than ideal clarity if the

agency’s path may reasonably be discerned.’” (quoting

Bowman Transp., Inc. v. Arkansas-Best Freight Sys., Inc., 419

U.S. 281, 286 (1974))).

New York next contends that EPA did not correctly take

into account commuting data for the outer counties and points

to its own data showing that only 13% of outer county

commuters drive to New York City. States’ Opening Br. 39.

EPA responds that the relevant factor on which it relied was

not the percentage of commuters but rather the raw number of

commuters. New York correctly highlights the inconsistency

in EPA’s treatment of Rockland County’s commuter data,

which is discussed below, but as to the other counties, New

York’s arguments are not persuasive. The Technical Support

Document shows that Westchester and Nassau Counties each

have over 100,000 commuters to New York and Bronx

Counties. Technical Support Document at 6-29. Suffolk

County has fewer commuters to New York and Bronx

Counties (roughly 44,000), but it has higher Vehicle Miles

Traveled (VMT) than either Westchester or Nassau Counties,

likely due to its location on eastern Long Island. Id. New

York is correct that Orange County’s commuter numbers and

VMT are far lower than any of the other three counties, id.,

but EPA based Orange County’s nonattainment designation

on its high emissions, not its commuter numbers, id. at 6-24.

EPA’s reliance on commuting data is supported by the record,

which shows significant numbers of commuters and VMT for

Westchester, Nassau, and Suffolk Counties.

52

New York also maintains that EPA impermissibly

changed its theory of outer county contribution from

contribution to a violating monitor in New Haven,

Connecticut, to contribution to violating monitors in

Manhattan and the Bronx. EPA’s initial rationale for

designation in the Technical Support Document reads:

“Nassau County ranks high for emissions, population, traffic,

and commuting patterns. In addition, an analysis of pollution

roses and back trajectories to New Haven, CT showed a

contribution from Nassau County.” Id. Based on comments

submitted by New York and Connecticut, EPA agreed that the

violating New Haven monitor was “not representative of

community exposure” and thus should not be the basis of

designations. See id. at 6-35. EPA did not, however, change

the outer counties’ designations on this ground.

New York’s claim that EPA’s continued nonattainment

designations were arbitrary fails because EPA’s rationale for

the designations can be discerned from the Technical Support

Document, which lists numerous reasons for designation other

than contribution to the New Haven monitor. It is a

reasonable reading of the Technical Support Document to

attribute the list of factors, such as emissions and commuters,

as referring to contribution to the violating monitors in

Manhattan and the Bronx, while the initial rationale for

contribution to New Haven was back trajectories and

pollution roses. More important, New York is protesting the

iterative process of revision that the CAA itself mandates:

EPA revised its position in response to New York’s

comments. New York’s underlying complaint is that the

iterations should have continued, perhaps ad infinitum. But

such a process is inconsistent with the CAA: Congress

imposed deadlines on EPA and thus clearly envisioned an end

to the designation process.

53

Although we reject New York’s challenge to the

designations of Westchester, Suffolk, Nassau, and Orange

Counties, the state’s challenge to Rockland County’s

nonattainment designation has merit. EPA appears to have

acted inconsistently in designating Rockland County as a

nonattainment area.

First, New York persuasively shows that Rockland’s

treatment was inconsistent with the treatment of other

counties in the same CMSA that fall within a different EPA

region. New York notes that EPA Region 1, which

encompasses the CMSA’s New England counties, employed

what New York terms an “80% test” in deciding which

counties would be designated nonattainment. The Region 1

materials do not reference such a test, but New York is correct

in its description of the process EPA Region 1 apparently

employed. Region 1 “dropped” from nonattainment

consideration Litchfield and Middlesex Counties in

Connecticut and Hampden and Berkshire Counties in

Massachusetts because: “(1) none of these counties contain

violating PM2.5 monitors, (2) none were recommended for

nonattainment designation by the state, and (3) all have

emissions scores ≤2.5.” Id. at 6-6. Region 1 arrived at the 2.5

cutoff by ranking all of the CMSA counties from highest to

lowest weighted emissions score, summing the weighted

emissions scores from top to bottom, and drawing a line after

the county at which the cumulative emissions score equaled

80%—thus, the “80% test.” Any counties below the 80% line

were dropped from further consideration if they did not

contain a violating monitor and were not recommended by the

state for a nonattainment designation. See id. at 6-4 to -6.

Although this may be a reasonable approach in the abstract,

New York’s complaint is that, if this process had

been applied in Region 2, which includes the New York

counties, Rockland County would have been dropped from

54

consideration instead of designated nonattainment. EPA

responds that the “80% test” was no test at all. But the

agency’s characterization is unavailing because no matter

how Region 1’s process is characterized, the fact remains that

Rockland County would have been designated attainment if it

had been in Region 1, but was designated nonattainment by

EPA Region 2. Such inconsistent treatment is the hallmark of

arbitrary agency action.

Second, EPA’s rationale for designating Rockland

County changed between the initial designation and the final

designation, with no apparent change in data. The only

rationale EPA cited in its initial designation of Rockland was

that Rockland “is contiguous to . . . Orange and Westchester

Counties,” both of which EPA designated as nonattainment.

Id. at 6-24. In the initial designations, EPA characterized

Rockland County’s commuter numbers as “low,” id. at 6-31;

when it revised its designations, EPA characterized Rockland

County’s commuter numbers as “significant,” though there

was no intervening change in data, id. at 6-35.

Third, and relatedly, New York argues that EPA treated

Rockland County differently than Dutchess County in New

York and Ocean County in New Jersey, both of which were

designated attainment. New York notes that both counties

have similar or worse values than Rockland on most or all of

the factors EPA assessed. EPA’s response, laid out in its brief

to this court, is that of the factors New York cites, only

commuting was significant for Rockland, and that Rockland’s

numbers of commuters to violating counties are three times

the same statistic for Dutchess and Ocean Counties. EPA also

notes that Rockland has large power plants, while Ocean

County does not. EPA Br. 154.

55

EPA’s attempt to distinguish Rockland County does not

withstand close inspection. First, EPA cannot rely on

Rockland’s power plants to distinguish Rockland from Ocean

County because power plants are solely a proxy for emissions,

and Rockland has lower emissions than either Ocean or

Dutchess County. Second, EPA is correct that, while

Rockland has three to four times the number of commuters to

violating counties as the other two counties, EPA initially

characterized Rockland’s commuter numbers as “low.” The

agency’s later rhetorical revision of its characterization to

“significant” is not justified by any change in the underlying

data, which renders suspect EPA’s reliance on commuters as

the sole basis for distinguishing Rockland from the other two

counties.

In sum, Rockland County’s nonattainment designation is

troubling because of the apparent inconsistency in EPA’s

approach to designations in different EPA regions, EPA’s

varying characterizations of Rockland’s statistics, and EPA’s

treatment of Rockland as compared to Dutchess and Ocean

Counties. In light of the agency’s scientific expertise and the

complexity of the designation process, we remand to give

EPA another opportunity to provide a coherent explanation

for its designation. See, e.g., North Carolina v. EPA, 550

F.3d 1176 (D.C. Cir. 2008).

B. Other Individual County Challenges

We have considered the other individual county

challenges lodged by Petitioners and conclude that none of

them has merit. Our standard of review is deferential. EPA

“must examine the relevant data and articulate a satisfactory

explanation for its action including a ‘rational connection

between the facts found and the choice made.’” State Farm,

463 U.S. at 43 (quoting Burlington Truck Lines, 371 U.S. at

56

168). The record before us shows that EPA considered

numerous relevant factors for each challenged county, and the

evidence supports the nonattainment designations EPA

promulgated. In the accompanying judgment, we deny the

petitions for review of the remaining individual county

designations.

VII.

Having considered petitioners’ remaining arguments and

finding them without merit, we deny the petitions for review

in all respects save one: the designation of Rockland County

is remanded to EPA.

So ordered.