# Air Plan Approval; Mississippi; 2010 1-Hour SO2 NAAQS Transport Infrastructure

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2026-17503

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** August 27, 2026
- **Citation:** 91 FR 55305

## Text

ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R04-OAR-2023-0227; FRL-13502-01-R4]

Air Plan Approval; Mississippi; 2010 1-Hour SO
2
NAAQS Transport Infrastructure

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

Pursuant to the Federal Clean Air Act (CAA or the Act), the U.S. Environmental Protection Agency (EPA or Agency) is proposing to approve a State Implementation Plan (SIP) revision submitted by the State of Mississippi, through the Mississippi Department of Environmental Quality (MDEQ), on January 27, 2022, for the purpose of complying with the “good neighbor” provision of the CAA for the 2010 1-hour sulfur dioxide (SO
2
) primary National Ambient Air Quality Standard (NAAQS). The good neighbor provision requires each State's implementation plan to contain adequate provisions prohibiting the interstate transport of air pollution in amounts that will contribute significantly to nonattainment, or interfere with maintenance, of a NAAQS in any other State. In this proposed rulemaking, the EPA is proposing to determine that Mississippi will not contribute significantly to nonattainment or interfere with maintenance of the 2010 1-hour SO
2
primary NAAQS in any other State. Therefore, the EPA is proposing to approve the January 27, 2022, SIP revision as meeting the requirements of the good neighbor provision for the 2010 1-hour SO
2
primary NAAQS.

DATES:

Comments must be received on or before September 17, 2026.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-R04-OAR-2023-0227 at
regulations.gov.
Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from
Regulations.gov
. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (
i.e.,
on the web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit
https://www.epa.gov/dockets/commenting-epa-dockets.

FOR FURTHER INFORMATION CONTACT:

Matthew Bloemer, Muti-Air Pollutant Coordination Section, Air Planning and Implementation Branch, Air and Radiation Division, U.S. Environmental Protection Agency, Region 4, 61 Forsyth Street SW, Atlanta, Georgia 30303-8960. The telephone number is (404) 562-9653. Mr. Bloemer can also be reached via electronic mail at
bloemer.matthew@epa.gov.

SUPPLEMENTARY INFORMATION:

Throughout this proposed rule, the use of “we,” “us,” or “our” is intended to refer to the EPA. We use multiple abbreviations and terms in this proposed rule. While this list may not be exhaustive, for ease of reading and for reference purposes, the EPA defines the following terms and acronyms here:

CAA Clean Air Act

CBI Confidential Business Information

CFR Code of Federal Regulations

DRR Data Requirements Rule

DV Design Value

EGU Electric Generating Unit

EIS Emissions Inventory System

EPA Environmental Protection Agency

FR Federal Register

km Kilometer

MDEQ Mississippi Department of Environmental Quality

MS Mississippi

NAAQS National Ambient Air Quality Standard

NEI National Emissions Inventory

NPRM Notice of Proposed Rulemaking

NSR New Source Review

Pb Lead

PM
2.5
Particulate Matter less than 2.5 µm in diameter

ppb Parts Per Billion

SIP State Implementation Plan

SO
2
Sulfur Dioxide

tpy Tons per year

TSD Technical Support Document

WOE Weight of Evidence

Table of Contents

I. Background

A. Infrastructure SIPs

B. 2010 1-Hour SO
2
NAAQS Designations Background

II. Relevant Factors Used To Evaluate 2010 1-Hour SO
2
Interstate Transport SIPs

III. Mississippi's SIP Submission and the EPA's Analysis

A. State Submission

B. The EPA's Evaluation Methodology

1. The EPA's Prong 1 Evaluation—Contribute Significantly to Nonattainment

2. The EPA's Prong 2 Evaluation—Interference With Maintenance

IV. Proposed Action

V. Statutory and Executive Order Reviews

I. Background

A. Infrastructure SIPs

On June 2, 2010, the EPA established a revised primary 1-hour SO
2
NAAQS with a level of 75 parts per billion (ppb), based on a 3-year average of the annual 99th percentile of daily maximum 1-hour average concentrations.
1

CAA section 110(a)(1) requires all States to submit, within three years after promulgation of a new or revised NAAQS, SIP submissions to provide for the implementation, maintenance, and enforcement of the NAAQS.
2

The EPA has historically referred to these SIPs as “infrastructure SIPs.” Specifically, CAA section 110(a)(1) provides the procedural and timing requirements for SIP submissions. CAA section 110(a)(2) lists specific elements that all States must meet related to a newly established or revised NAAQS, such as requirements for monitoring, basic program requirements, and legal authority that are designed to assure attainment and maintenance of the NAAQS.

1

See
75 FR 35520 (June 22, 2010).

2
On December 10, 2024, the EPA revised the existing secondary SO
2
standard to an annual standard of 10 ppb, averaged over 3 years.
See
89 FR 105692 (Dec. 27, 2024).

CAA section 110(a)(2)(D)(i)(I), also known as the “good neighbor” provision, requires a State's implementation plan to include adequate provisions prohibiting any source or other type of emissions activity in the State from emitting any air pollutant in amounts that will contribute significantly to nonattainment, or interfere with maintenance, of the NAAQS in any other State. The EPA has long interpreted this language to enact a “functional prohibition” on certain emissions from upwind States, necessitating the EPA's independent assessment whether those emissions will occur or have been adequately controlled in the State where they originate.
3

The EPA often refers to these requirements as prong 1 (significant contribution to nonattainment of the NAAQS) and prong 2 (interference with maintenance of the NAAQS).
4

This notice of proposed rulemaking (NPRM) addresses Mississippi's good neighbor obligations pursuant to prongs 1 and 2. All other applicable infrastructure SIP requirements of CAA section 110(a)(2) for the 2010 1-hour SO
2
NAAQS for Mississippi, except for prong 4, have been addressed in separate rulemakings.
5

3

See Genon Rema LLC
v.
EPA,
722 F.3d 513, 520-24 (3d Cir. 2013);
Appalachian Power Co.
v.
EPA,
249 F.2d 1032, 1045-47 (D.C. Cir. 2001);
see also
71 FR 25328, 25335 (Apr. 28, 2006) (explaining that the SIP/FIP process under CAA section 110 and the petitioning process for direct Federal regulation under CAA section 126 provide independent means of effectuating the same “functional prohibition” found in CAA section 110(a)(2)(D)(i)(I)).

4
CAA section 110(a)(2)(D)(i) includes four distinct components, commonly referred to as “prongs,” that must be addressed in infrastructure SIP submissions. The first two prongs, which are codified in CAA section 110(a)(2)(D)(i)(I), prohibit any source or other type of emissions activity in one State from contributing significantly to nonattainment of the NAAQS in another State (prong 1) and from interfering with maintenance of the NAAQS in another State (prong 2). The third and fourth prongs, which are codified in CAA section 110(a)(2)(D)(i)(II), prohibit emissions activity in one State from interfering with measures required to prevent significant deterioration of air quality in another State (prong 3) or from interfering with measures to protect visibility in another State (prong 4).

5
The EPA took action to approve Mississippi's remaining infrastructure elements, except for CAA section 110(a)(2)(D)(i)(II), prong 4, on September 30, 2016 (81 FR 67178) and October 4, 2018 (83 FR 50014). The EPA will address prong 4 in a separate rulemaking.

B. 2010 1-Hour SO
2
NAAQS Designations Background

In this proposed rulemaking, the EPA has considered information from the 2010 1-hour SO
2
NAAQS designations process, as discussed in more detail in the Technical Support Document (TSD) for this rulemaking. For this reason, a summary of the EPA's designations process for the 2010 1-hour SO
2
NAAQS is included here.
6

6
While designations may provide useful information for purposes of analyzing transport, the EPA notes that designations themselves are not dispositive of whether or not upwind emissions are impacting areas in downwind States. The EPA has consistently taken the position that CAA section 110(a)(2)(D)(i)(I) requires elimination of significant contribution and interference with maintenance in other States, and this analysis is not limited to designated nonattainment areas. Nor must designations for nonattainment areas have first occurred before States or EPA can act under CAA section 110(a)(2)(D)(i)(I).
See, e.g.,
Clean Air Interstate Rule, 70 FR 25162, 25265 (May 12, 2005); Cross State Air Pollution Rule, 76 FR 48208, 48211 (Aug. 8, 2011); Final Response to Petition from New Jersey Regarding SO
2
Emissions From the Portland Generating Station, 76 FR 69052 (Nov. 7, 2011) (finding facility in violation of the prohibitions of CAA section 110(a)(2)(D)(i)(I) with respect to the 2010 1-hour SO
2
NAAQS prior to issuance of designations for that standard).

After the promulgation of a new or revised NAAQS, the EPA is required to designate areas as “nonattainment,” “attainment,” or “unclassifiable” pursuant to CAA section 107(d)(1)-(2). The process for designating areas following promulgation of a new or revised NAAQS is contained in section 107(d) of the CAA. The EPA promulgated the 2010 1-hour SO
2
NAAQS on June 2, 2010.
7

The EPA Administrator signed the first round
8

of designations (Round 1)
9

for the 2010 1-

hour SO
2
NAAQS on July 25, 2013, designating 29 areas in 16 States as nonattainment for the 2010 1-hour SO
2
NAAQS.
10

The
Federal Register
final rules of promulgation for Round 2 designations
11

published on July 12, 2016 and on December 13, 2016.
12 13

Round 3 designations
14

were published on January 9, 2018 and April 5, 2018.
15 16

Round 4 designations
17

were published on March 26, 2021 and April 14, 2021.
18 19 20

The Agency published the Data Requirements Rule (DRR) on August 21, 2015 to provide expectations for collection of data, either monitoring or modeling, for the remaining designations.
21 22

In the DRR, the EPA identified six sources in Mississippi for which the State was required to characterize air quality through modeling or monitoring or impose federally enforceable controls. In Round 2 designations, the EPA designated Lamar County as attainment/unclassifiable based on modeling, effective August 12, 2016.
23

In Round 3, the EPA designated Choctaw and Jackson Counties as attainment/unclassifiable based on modeling, effective April 9, 2018.
24

Also, during Round 3, the EPA designated the remaining counties without DRR sources as attainment/unclassifiable, completing the area designations for the 2010 1-hour SO
2
NAAQS in Mississippi effective April 9, 2018. Thus, no areas in the State were designated in Round 4. Currently, there are no nonattainment areas in Mississippi for the 2010 1-hour SO
2
NAAQS based on Rounds 1 through 4.

7

See
75 FR 35520 (June 22, 2010).

8
The term “round” in this instance refers to which “round of designations.”

9
The EPA and State documents and public comments related to the Round 1 final designations are in the docket at
regulations.gov
with Docket ID No. EPA-HQ-OAR-2012-0233 and at the EPA's website for SO
2
designations at
https://www.epa.gov/sulfur-dioxide-designations.

10

See
78 FR 47191 (Aug. 5, 2013).

11
The EPA and State documents and public comments related to the Round 2 final designations are in the docket at
regulations.gov
with Docket ID No. EPA-HQ-OAR-2014-0464 and at the EPA's website for SO
2
designations at
https://www.epa.gov/sulfur-dioxide-designations.

12

See
81 FR 45039.

13

See
81 FR 89870.

14
The EPA and State documents and public comments related to Round 3 final designations are in the docket at
regulations.gov
with Docket ID No. EPA-HQ-OAR-2017-0003 and at the EPA's website for SO
2
designations at
https://www.epa.gov/sulfur-dioxide-designations.

15

See
83 FR 1098.

16

See
83 FR 14597.

17
The EPA and State documents and public comments related to Round 4 final designations are in the docket at
regulations.gov
with Docket ID No. EPA-HQ-OAR-2020-0037 and at the EPA's website for SO
2
designations at
https://www.epa.gov/sulfur-dioxide-designations.

18
The Round 4 2010 1-hour SO
2
NAAQS designations action was signed by former EPA Administrator Andrew Wheeler on December 21, 2020, pursuant to a court-ordered deadline of December 31, 2020. For administrative purposes only, and in compliance with requirements of the Office of the Federal Register, former Acting Administrator Jane Nishida re-signed the same action on March 10, 2021, for publication in the
Federal Register
.

19

See
86 FR 16055.

20

See
86 FR 19576.

21

See
80 FR 51052.

22
On August 21, 2015 (80 FR 51052), the EPA separately promulgated air quality characterization requirements for the 2010 1-hour SO
2
NAAQS in the DRR. The DRR requires State air agencies to characterize air quality, through air dispersion modeling or monitoring, in areas associated with sources that emitted in 2014 2,000 tpy or more of SO
2
, or that have otherwise been listed under the DRR by the EPA or State air agencies. In lieu of modeling or monitoring, State air agencies, by specified dates, could elect to impose federally enforceable emissions limitations on those sources restricting their annual SO
2
emissions to less than 2,000 tpy, or provide documentation that the sources have been shut down. The EPA used the information generated by implementation of the DRR to help inform round 4 designations for the 2010 1-hour SO
2
NAAQS.

23

See
81 FR 45039 (July 12, 2016) and EPA's
Final Technical Support Document: Mississippi—Area Designations for the 2010 SO
2
Primary National Ambient Air Quality Standard,
at
https://www.epa.gov/sites/default/files/2016-07/documents/r4_ms_final_designation_tsd_06302016.pdf.

24

See
83 FR 1098 (Jan. 9, 2018) and
Technical Support Document: Chapter 21 Final Round 3 Area Designations for the 2010 1-Hour SO
2

Primary National Ambient Air Quality Standard for Mississippi,
at
https://www.epa.gov/sites/default/files/2017-12/documents/21-ms-so2-rd3-final.pdf.

II. Relevant Factors Used To Evaluate 2010 1-Hour SO
2
Interstate Transport SIPs

Although SO
2
is emitted from a similar universe of point and nonpoint sources as is directly emitted fine particulate matter (PM
2.5
) and the precursors to ozone and PM
2.5
, interstate transport of SO
2
is unlike the transport of PM
2.5
or ozone, which disperse over a wide area and can contribute to nonattainment or maintenance issues hundreds of miles from precursor-emitting sources or activities. SO
2
emissions usually do not undergo long-range transport in the atmosphere. The transport of SO
2
relative to the 2010 1-hour SO
2
NAAQS is more analogous to the transport of lead (Pb) relative to the Pb NAAQS in that emissions of SO
2
typically result in 1-hour pollutant impacts of greatest concern near the emissions source. However, ambient 1-hour concentrations of SO
2
do not decrease as quickly with distance from the source as do 3-month average concentrations of Pb, because SO
2
gas is not removed by deposition as rapidly as are Pb particles. Emitted SO
2
has wider-ranging impacts than emitted Pb, but it does not have such wide-ranging (far downwind) impacts that treatment in a manner similar to ozone or PM
2.5
would be appropriate. Accordingly, the approaches that the EPA has adopted for ozone or PM
2.5
transport are too regionally focused, and the approach for Pb transport is too tightly circumscribed to the source, to be appropriate for assessing SO
2
transport. SO
2
transport is therefore a unique case and necessitates an approach that lies between these other approaches to assessing pollutant transport.

In this NPRM, and consistent with prior SO
2
transport analyses, the EPA focused on a 50 kilometer (km)-wide zone around sources of interest because the physical properties of SO
2
result in relatively localized pollutant impacts near an emission source that drop off with distance. Given the properties of SO
2
, the EPA believes that significant impacts in a downwind State are unlikely at distances greater than 50 km from a source and thus, the EPA's review focused on areas within 50 km of the State lines. This scale of analysis is consistent with the “urban scale” which is the largest appropriate spatial scale for SO
2
monitors and is useful for assessing SO
2
transport and trends in area-wide air quality.
25

25
For the definition of spatial scales for SO
2
,
see
40 CFR part 58, appendix D, section 4.4 (“Sulfur Dioxide (SO
2
) Design Criteria”). For further discussion on how the EPA applies these definitions with respect to interstate transport of SO
2, see
the EPA's proposed rulemaking on Connecticut's SO
2
transport SIP.
See
82 FR 21351, 21352, 21354 (May 8, 2017).

As discussed in section III of this document, and in further detail in the TSD for this proposed rulemaking, the EPA reviewed Mississippi's January 27, 2022, SO
2
SIP submission. Mississippi's submission did not provide enough data to completely assess whether the State was meeting its CAA good neighbor requirements for the 2010 SO
2
NAAQS. Therefore, the EPA elected to review and assess other available information regarding SO
2
emissions and air quality for sources in Mississippi to assist in this evaluation given the availability of more recent emissions, air quality data, and air dispersion modeling that was not available at the time of Mississippi's submittal. The EPA independently analyzed such information to determine whether Mississippi meets the interstate transport requirements described in the CAA.
26

26
This proposed rulemaking is based on the information contained in the administrative record for this proposed rulemaking and does not prejudge any future EPA action that may make other determinations regarding the air quality status in Mississippi and downwind States. Any such future action, such as area designations under any NAAQS, would be based on separate administrative records and the EPA's analyses of information that become available at that time. Future available information may include, monitoring data and modeling analyses conducted by States, air agencies, and third-party stakeholders.

Consistent with our prior evaluations of other States' SO
2
transport obligations, the EPA conducted a weight of evidence (WOE) analysis evaluating

several sources of information, including current air quality data from monitors as well as available emissions and/or source modeling for sources in Mississippi and neighboring States within 50 km of the State border. A WOE approach can be appropriate in instances, such as in this case, to determine whether or not SO
2
emissions from Mississippi contribute to nonattainment or maintenance issues in adjoining States. A WOE analysis that is based strictly on available data may not be sufficient in all instances for evaluating interstate SO
2
transport, and additional analysis may be necessary. Further, the term “WOE” does not establish the legal or technical meaning for what constitutes significant contribution to nonattainment or interference with maintenance for the 2010 SO
2
NAAQS. Rather, the term refers to the gathering and consideration of a wide range of information, on a case-by-case basis, to determine whether a statutory or regulatory standard is met.

In other SO
2
transport SIP actions, the EPA has generally been able to use a WOE analysis of available information to reach a conclusion that there are no SO
2
nonattainment or maintenance issues in the relevant areas of other States, or that no sources in the upwind State are contributing to those issues. If the available evidence indicated, however, that an upwind source, sources, or emissions activities were contributing to an out-of-State SO
2
nonattainment or maintenance problem, then further analysis and a regulatory determination would be necessary concerning what amount of those emissions, if any, constituted “significant contribution” under prong 1 or prong 2 of the good neighbor provision.

The EPA finds there is sufficient information to allow the EPA to make a determination that no Mississippi sources are contributing to any out-of-State SO
2
nonattainment or maintenance concerns under current and likely future conditions and emissions scenarios; therefore, it is not necessary for purposes of this action to render a determination concerning what amount of emissions would be “significant” and therefore subject to prohibition under the good neighbor provision.
27

27

Cf. Genon Rema
v.
EPA,
722 F.3d 513 (3d Cir. 2013) (upholding the EPA grant of CAA section 126(b) petition and establishment of direct Federal emissions control requirements on SO
2
source in Pennsylvania found to be significantly contributing to nonattainment and interfering with maintenance of the 2010 SO
2
NAAQS in New Jersey).

III. Mississippi's SIP Submission and the EPA's Analysis

A. State Submission

Mississippi's January 27, 2022, SIP submission addresses the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2010 1-hour SO
2
primary NAAQS. Mississippi conducted an analysis to examine whether SO
2
emissions from Mississippi contribute significantly to nonattainment, or interfere with maintenance of, the 2010 1-hour SO
2
NAAQS in downwind States.

Mississippi based its conclusions for prongs 1 and 2 on the following information: SO
2
design values (DVs)
28

for the years 2012-2014 at monitors in Mississippi and in the neighboring States (Alabama, Tennessee, and Louisiana); statewide SO
2
actual emissions from 2008 and 2011 and emission trends in this data; stationary source (electric generating units) actual SO
2
emissions from 2002-2017 and emissions trends in this data; Mississippi's initial work to meet the DRR requirements; State and Federal measures that establish requirements for sources of SO
2
emissions; monitored ambient air data in Mississippi and neighboring States based on a 50 km spatial distance; available DRR air dispersion modeling associated with relevant SO
2
sources in Mississippi and in neighboring States within 50 km of Mississippi's border; and an SO
2
source specific emission analysis from stationary sources in Mississippi and neighboring States that were not subject to the DRR that emitted over 100 tons per year (tpy) of SO
2
emissions in 2018 or 2019 within 50 km of the State's border (
i.e.,
an analyses of non-DRR sources' current emissions relative to the distance to the State's border).

28
A “Design Value” is a statistic that describes the air quality status of a given location relative to the level of the NAAQS. The DV for the primary 2010 1-hour SO
2
NAAQS is the 3-year average of annual 99th percentile daily maximum 1-hour values for a monitoring site. For example, the 2017 DV is calculated based on the three-year average from 2015-2017. The interpretation of the primary 2010 1-hour SO
2
NAAQS including the data handling conventions and calculations necessary for determining compliance with the NAAQS can be found in appendix T to 40 CFR part 50.

Based on this analysis, MDEQ concluded that no sources in the State are significantly contributing to nonattainment or interfering with maintenance of the 2010 SO
2
NAAQS in a neighboring State. Thus, Mississippi determined that the SIP contains adequate provisions to address the State's CAA good neighbor obligations.

The EPA's evaluation of Mississippi's submission is detailed in section III.B of this document below. The EPA may elect to consider additional information to assist in reaching a conclusion as to whether the submission may be approved, in whole or in part, as satisfying the Act's requirements, or does not meet the Act's requirements. Here, the EPA may consider all relevant information, or generate new data and analysis, to make an independent judgment in evaluating States' compliance with the good neighbor provision, which concerns the effects of States' emissions in other States. Therefore, the EPA elected to supplement Mississippi's transport SIP analysis with a review and assessment of other available information, as described below and in more detail in the TSD for this proposed rulemaking, regarding SO
2
emissions and air quality for sources in Mississippi to assist in the EPA's evaluation and to fully assess whether Mississippi is meeting its CAA good neighbor obligations for the 2010 SO
2
NAAQS.

B. The EPA's Evaluation Methodology

For this CAA section 110(a)(2)(D)(i)(I) evaluation of the 2010 SO
2
NAAQS, the EPA conducted a WOE analysis for prong 1 and prong 2 separately,
29

evaluating available information such as SO
2
ambient air data, emission inventory trends, modeling, and emission trends in Mississippi and the States that border Mississippi. The EPA has evaluated this information and further supplements Mississippi's analysis here to ensure there are no further SO
2
emissions controls needed for meeting CAA interstate transport requirements. To identify which sources and emissions activities in Mississippi could potentially impact downwind air quality in other States with respect to the 2010 1-hour SO
2
NAAQS, the EPA used information in the EPA's National Emissions Inventory (NEI)
30

and Emissions Inventory System (EIS).
31

The NEI is a comprehensive and detailed estimate of air emissions for criteria pollutants, criteria pollutant precursors, and hazardous air pollutants

from air emissions sources, updated every three years using information provided by the States and other information available to the EPA. For the identification of sources and emissions activities, the EPA largely relied on data from the 2020 NEI because it is the most recently available, complete, and quality assured dataset. However, in evaluating emissions trends, both State-wide and at the facility level, the EPA also considered data from prior NEI reports and EIS queries as part of the overall WOE analysis.

29
In
North Carolina
v.
EPA,
531 F.3d 896, 910-911 (D.C. Cir. 2008), modified, 550 F. 3d 1176 (D.C. Cir. 2008), the United States Court of Appeals for the District of Columbia Circuit (D.C. Cir.) explained that the regulating authority must give prong 2 “independent significance” from prong 1 by evaluating the impact of upwind State emissions on downwind areas that, while currently in attainment, are at risk of future nonattainment.

30
The EPA's NEI is available and accessible to the public at
https://www.epa.gov/air-emissions-inventories/national-emissions-inventory.

31
The EIS is the EPA's database used to receive and store emissions data and generate emissions inventories. The EIS Gateway is a web-based tool developed to provide only registered EPA, State, local and Tribal users with access to emission inventory data for sources in their jurisdiction.

As shown in table 1 below, the majority of SO
2
emissions in Mississippi originate from point sources. In 2020, total SO
2
emissions from point sources in Mississippi comprised approximately 56 percent of the total SO
2
emissions in the State. Nonpoint sources, on road, and nonroad emissions sources are individually much smaller and more dispersed throughout the State and are therefore unlikely to contribute to high ambient concentrations when compared to point source contributions. Further analysis
32

shows that facilities with reported emissions greater than 100 tpy represent approximately 4 percent of the total number of Mississippi SO
2
point sources but are responsible 5,411 tons of SO
2
, or 84 percent of the total 2020 reported SO
2
emissions originating from point sources in Mississippi.
33

Based on this analysis, the EPA's WOE analysis focused on SO
2
emissions from Mississippi's point sources (
i.e.,
sources emitting over 100 tpy of SO
2
) that are located within 50 km of one or more State borders.
34

The EPA's WOE analysis includes some of the same sources included in Mississippi's non-DRR source specific analysis.

32

See the
EPA's TSD for a more detailed discussion.

33

See
Table 9 in the EPA's TSD.

34

See
Table 10 in the EPA's TSD.

Table 1—Summary of 2020 SO
2
Emissions in Mississippi by Source Category

Category

2020 Emissions
(tpy)

Percent total SO
2
emissions

Point
6,420
56

Nonpoint
4,897
43

On Road
128
1

Nonroad
8
0

SO
2
Emission Total

11,453
100

As described in this section III of this document, the EPA proposes that an assessment of Mississippi's satisfaction of the prong 1 and 2 requirements under CAA section 110(a)(2)(D)(i)(I) for the 2010 1-hour SO
2
NAAQS may be reasonably based upon several factors. These factors include 2020-2022 through 2022-2024 ambient air quality SO
2
design value concentrations in Mississippi and surrounding States, 2022 SO
2
emission trends data for sources in Mississippi and neighboring States (assessing sources' current emissions relative to distance from the border), assessment of Mississippi's SO
2
point source 2022 emissions of more than 100 tpy of SO
2
per facility that are located within approximately 50 km of another State, assessment of other States' point sources emitting more than 100 tpy of SO
2
located within approximately 50 km of Mississippi, evaluation of the predicted downwind impacts projected in previous relevant modeling studies that have been conducted for certain sources, review of wind and topographic data to evaluate the likely direction of transport and magnitude of SO
2
emissions from relevant sources, and assessment of Federal regulations and SIP-approved regulations affecting Mississippi's SO
2
sources. The EPA's evaluation is informed by all available data at the time of this proposed rulemaking, including the analysis Mississippi provided in its January 27, 2022, SIP submission.
35

35
The EPA notes that the evaluation of other States' satisfaction of CAA section 110(a)(2)(D)(i)(I) for the 2010 1-hour SO
2
NAAQS can be informed by similar factors found in this proposed rulemaking but may not be identical to the approach taken in this or any future rulemaking for Mississippi, depending on available information and State-specific circumstances.

The EPA notes that if this information were insufficient to draw a reasonable conclusion concerning whether Mississippi is “significantly contributing” or not, then it would not be possible to propose approval based only on this information. In other words, in general, the absence of information concerning whether interstate transport is occurring is not in itself sufficient justification for approving a good neighbor SIP submission. For example, if there were inadequate monitoring or modeling information to characterize the effects of a large, near-border source of SO
2
emissions, it may be appropriate to conduct, or ask the State to conduct, further analysis to better characterize that source and its effects, in order to reach a determination concerning whether the good neighbor provision is being met.
36

In this case, the information available to the EPA, as analyzed in the accompanying TSD and summarized below, is fully sufficient to conclude that under current and likely future conditions and emissions scenarios Mississippi is not emitting and will not emit SO
2
pollution in violation of the good neighbor provision for the 2010 SO
2
NAAQS.

36

See, e.g.,
88 FR 41344 (June 26, 2023) (proposing approval of Tennessee's SO
2
good neighbor SIP submission based on updated modeling conducted to better characterize emissions from the Eastman Chemical facility).

1. The EPA's Prong 1 Evaluation—Contribute Significantly to Nonattainment

Prong 1 of the “good neighbor” provision requires States' plans to prohibit emissions that will contribute significantly to nonattainment of the NAAQS in another State. The EPA's evaluation
37

of whether Mississippi has met its prong 1 transport obligations was accomplished by considering all available information including the following: SO
2
ambient air quality in Mississippi and neighboring States; SO
2
emissions trends for Mississippi and neighboring States; potential ambient impacts of SO
2
emissions from certain facilities
38

in Mississippi on neighboring States; Mississippi's SIP-approved regulations specific to SO
2
emissions and to permit requirements;

and other SIP-approved or federally enforceable regulations which may reduce SO
2
emissions either directly or indirectly.

37
A detailed review of the EPA's evaluation of emissions, air monitoring data, other technical information, and rationale for proposed approval of this SIP revision as meeting CAA section 110(a)(2)(D)(i)(I) for the 2010 1-hour SO
2
NAAQS may be found in the TSD.

38
The physical properties of SO
2
result in relatively localized pollutant impacts near the emissions source. Therefore, the EPA selected a spatial scale with dimensions up to 50 km from point sources.

Based on the EPA's analysis, the Agency proposes to determine that there are no SO
2
nonattainment issues in the relevant areas in other States bordering Mississippi, and as such, the EPA proposes to determine that Mississippi's SIP satisfies the requirements of prong 1 of CAA section 110(a)(2)(D)(i)(I). This proposed determination is based on the following considerations:

• Monitors in neighboring Alabama, Louisiana, and Tennessee within 50 km of Mississippi's border all have DVs below the standard; there are no monitors recording violations of the 2010 1-hour SO
2
NAAQS located in Mississippi within 50 km of its border; and there are only two SO
2
monitors in Mississippi and neither are violating the 2010 SO
2
NAAQS. Only one of the two Mississippi monitors is within 50 km of the State's border, and the current DVs
39

at these two monitors are well below the 2010 SO
2
NAAQS and have remained well below the standard for many years;

39
The design value is the 3-year average of the 99th percentile 1-hour daily maximums at a monitor. A control strategy should be designed to bring the value to attainment of the standard.

• Downward SO
2
emission trends in Mississippi and in Alabama, Louisiana, and Tennessee, when considered together with the other factors discussed as part of Mississippi's analysis and the EPA's WOE, support Mississippi's conclusion that sources in the State will not contribute significantly to any other States' nonattainment of the 2010 1-hour SO
2
NAAQS; and

• Source-specific analyses of sources located within 50 km of the State border that emitted 100 tpy or more of SO
2
indicate that these sources do not contribute significantly to nonattainment in other States. These analyses draw upon available emissions data, monitoring data, air dispersion modeling, source retirements, wind rose data, and other relevant information to assess the likelihood of air quality impacts from these sources to areas in surrounding States. A detailed discussion of each source-specific analysis is contained in section IV.B.1.iii of the EPA's TSD accompanying this proposed rulemaking.

Below, the EPA covers some of the principal evidence that confirms that emissions from Mississippi do not contribute significantly to nonattainment in other States.
40

40
Unless otherwise stated, the summaries below include Mississippi sources listed in Table 10 of the TSD (and Tables 7 and 8 in Mississippi's submission) already established as meeting the 50 km spatial distance and 100 ton emission threshold for further analysis. This includes references to the EPA Region 6's WOE analysis regarding the Louisiana SO
2
transport infrastructure SIP revision.

a.
North Mississippi:
The EPA evaluated two sources in north Mississippi—Rockwool (formerly Roxul USA, Inc.) and Mississippi Silicon. Considering the short distance (approximately 2 km) from Rockwool to the Tennessee border, the EPA looked at available wind rose data (2021-2023) at the Olive Branch Airport in DeSoto County, Mississippi (the nearest wind rose west of Rockwool). This data shows predominant wind patterns from the south, southeast, and southwest suggesting that Rockwool emissions are most likely carried north into Tennessee possibly interacting with the Shelby Farms monitor and Memphis Airport. However, the EPA assessed prevention of significant deterioration (PSD) permit modeling for Rockwool performed in 2012
41

and 2016,
42

including modeling of SO
2
to determine compliance with the 1-hour SO
2
NAAQS. The results showed Rockwool did not cause or contribute to any violations of the 1-hour SO
2
NAAQS in either Mississippi or across the border in Tennessee. Both sets of modeling included cumulative impacts above the 1-hour SO
2
NAAQS, but in both analyses, the contribution from the Rockwool facility to the modeled violations was very small (<0.11 microgram per cubic meter (µg/m
3
)), which is well below the 1-hour SO
2
Significant Impact Level (SIL) of 7.8 µg/m
3
.

41
The PSD Air Permit Application, Volume III, Dispersion Modeling, Roxul USA, Inc., March 2012, Prepared by ERM.

42
Volume II: Update to PSD Air Quality Assessment, Roxul USA, Inc. August 2016, Prepared by ERM.

For Mississippi (MS) Silicon, the EPA looked at available wind rose data (2021-2023). This data shows predominant wind patterns from the south and southeast suggesting that emissions are likely transported northward into Tennessee possibly interacting with the nearest Tennessee source, Package Corporation of America. However, the EPA also considered 2014
43

and 2021
44

PSD permit modeling for MS Silicon where both modeling analyses were performed to demonstrate compliance with the 1-hour SO
2
NAAQS in accordance with PSD permitting requirements. The results of the modeling show that MS Silicon did not cause or contribute to any violations of the 1-hour SO
2
NAAQS in either Mississippi or across the borders in Tennessee and Alabama. The available modeling for MS Silicon, discussed further in the EPA's TSD, supports a determination that the source does not contribute significantly to nonattainment of the NAAQS in Tennessee or Alabama.

43
Mississippi Department of Environmental Quality, Modeling Report, Mississippi Silicon LLC, Tishomingo County, MS, November 2014, Prepared by FC&E Engineering LLC.

44
Mississippi Silicon Air Quality Impact Assessment, Report in Support of Air Permit Amendment Request, August 17, 2021, Prepared by Kennedy/Jenks Consultants.

b.
East Mississippi:
For the three Lowndes County sources—Steel Dynamics Columbus (SDI), International Paper Columbus Mill (IP-Columbus Mill), and the Columbus Air Force Base (AFB). These sources are approximately 27 km, 15 km, and 17 km, respectively, from the Alabama State border. In 2022, these sources emitted approximately 370 tpy, 215 tpy, and 239 tpy, respectively. From 2020-2022, these sources collectively emitted 912 tpy or less per year. The distance between the closest Lowndes County source (IP-Columbus Mill) and the nearest Alabama source (Nucor Steel in Tuscaloosa) is 90 km. Wind rose data showing predominant winds from the south, southeast, and north indicate that emissions from these sources will predominately not be transported across the Alabama border. Based on all of this, the EPA believes these three sources in Lowndes County are not interacting in such a way that they will significantly contribute to nonattainment or interfere with maintenance in Alabama.

c.
West Mississippi:
The low SO
2
emissions (under 100 tpy in 2023) from IP-Vicksburg in Warren County, infrequent winds toward Louisiana, the large distance between the closest Louisiana source, GPI, in Ouachita Parish, and IP-Vicksburg (129 km) (suggesting the respective plumes would be too far apart to interact), and the Mississippi-Louisiana border (98 km), all suggest an unlikely cumulative impact in Louisiana. Thus, the EPA believes it is unlikely that emissions from IP-Vicksburg could contribute significantly to nonattainment of the 2010 SO
2
NAAQS in Louisiana.

d.
South Mississippi:

i. Lamar County

There are no nearby SO
2
sources in Mississippi or Louisiana within 50 km of the Rain CII Carbon LLC (Rain-MS) facility in Lamar County that emitted greater than 100 tpy of SO
2
that could interact with the facility and create a potential cumulative downwind transport of SO
2
emissions into Louisiana to cause a violation of the 2010 standard. The closest Louisiana source—International Paper-Bogalusa

Mill (IP-Bogalusa Mill)—is approximately 64 km southwest of Rain. Additionally, available 2021-2023 wind rose data shows predominant wind patterns from the south and north and less frequently from the northwest and southeast in the path of Rain-MS suggesting a low frequency of winds blowing from Rain-MS towards Louisiana. With the distance from Rain-MS to the Louisiana border and IP-Bogalusa greater than 50 km, the consistent trend in annual SO
2
emissions at Rain-MS over the past 10 years,
45

no evidence of modeled cumulative impacts with the nearby R.D. Morrow DRR, and the repowering of emission units at Morrow, the EPA believes it is unlikely that Rain-MS could interact with these sources to contribute significantly to nonattainment of the SO
2
NAAQS in Louisiana. Furthermore, there are no nearby SO
2
sources in Mississippi or Louisiana within 50 km of Rain that emitted greater than 100 tpy of SO
2
that could interact with the facility and create potential cumulative downwind impacts.
46

45
Even though preliminary 2023 emissions at Rain show an increase of approximately 20 tons, this increase is not a significant outlier in the trends from the past 10 years when Rain has shown a downward trend from 746.14 tons since 2013 and has stable emissions between 377 and 347 tpy since 2017.

46

See
“Air Plan Approval; Louisiana; Interstate Transport Requirements for the 2010 SO
2
NAAQS.” 90 FR 15213 (Apr. 9, 2025) and 90 FR 29743 (July 7, 2025).
See also
EPA's TSD for the Louisiana rulemaking in Docket No. EPA-R06-OAR-2013-0465.

ii. Jackson County

Wind rose data near Chevron Texaco Products (Chevron) petroleum refinery in Jackson County, Mississippi indicates a low frequency of west to east winds in the path of Chevron towards the Alabama border and the W&T Offshore and Evonik sources in southeast Mobile County. The 80 km spatial distance between Chevron and Alabama Power Plant Barry Generating Station and Nouryon in northwest Mobile County is also too far for their respective plumes to interact and contribute significantly to SO
2
NAAQS nonattainment in Alabama. The EPA also believes it is unlikely that emissions from Chevron and the two sources in the St. Bernard Parish SO
2
nonattainment area (Chalmette Refining LLC and Rain CII Carbon-Louisiana) could interact as to contribute significantly to SO
2
NAAQS nonattainment in Louisiana.
47

Based on this weight of evidence, the EPA concludes that emissions from Chevron are not contributing significantly to SO
2
NAAQS nonattainment in Alabama or Louisiana.

47

See
the TSD in Docket No. EPA-R06-OAR-2013-0465 for EPA's WOE analysis of sources in the St. Bernard Parish SO
2
NAA supporting the EPA's approval of Louisiana's SO
2
Interstate Transport SIP.
See
“Air Plan Approval; Louisiana; Interstate Transport Requirements for the 2010 SO
2
NAAQS.” 90 FR 29743 (July 7, 2025).

The Pascagoula monitor, located approximately 5 km northwest of Chevron in Jackson County, 13 km west of the Alabama border, and 80 km north of St. Bernard Parrish, Louisiana, measured less than 6 ppb from 2018 through 2024. This monitor was not sited to characterize the maximum SO
2
concentrations from Chevron, however, the EPA believes the low design value provides a good indication that Chevron's SO
2
concentrations near the Alabama border are likely well below the 1-hr SO
2
NAAQS.

Based on this evaluation, discussed further in the EPA's TSD, EPA proposes to find that SO
2
sources in Mississippi will not contribute significantly to nonattainment of the 2010 1-hour SO
2
NAAQS in any other State.

2. The EPA's Prong 2 Evaluation—Interference With Maintenance

Prong 2 of the “good neighbor” provision requires State plans to prohibit emissions that will interfere with maintenance of a NAAQS in another State. The EPA's evaluation of whether Mississippi has met its prong 2 transport obligations was accomplished by considering all available information, with a focus on current air quality data, SO
2
emission trends for Mississippi and neighboring States, and how existing and future sources of SO
2
are addressed through existing SIP-approved and other federally enforceable regulations. This evaluation builds upon the analysis conducted for significant contribution to nonattainment (prong 1), which considered SO
2
ambient air quality in Mississippi and neighboring States and potential ambient impacts of SO
2
emissions from certain facilities in Mississippi on neighboring States.

Based on the EPA's analysis, we propose to find that SO
2
levels in neighboring States near the Mississippi border do not indicate an inability to maintain the SO
2
NAAQS that could be attributed in part to sources in Mississippi. As such, the EPA proposes to determine that Mississippi's SIP satisfies the requirements of prong 2 of CAA section 110(a)(2)(D)(i)(I). This determination is based on the following considerations:

• The current 2022-2024 DV for the SO
2
monitor in Mississippi within 50 km of another State's border and in neighboring States within 50 km of Mississippi's border are below the standard, indicating that these areas are all currently in attainment of the 2010 1-hour SO
2
NAAQS;

• State-wide SO
2
emission trends in Mississippi and surrounding States are generally declining thus resulting in declining impacts to neighboring States;

• Source-specific analyses show that Mississippi facility-level emissions are generally decreasing considering Federal and SIP-approved provisions regulating SO
2
emission standards, indicating that emissions are not anticipated to increase relative to baseline emissions;

• Current Mississippi SIP-approved measures and Federal SO
2
emission requirements control SO
2
emissions from specific source sectors within Mississippi; and

• Mississippi's SIP-approved PSD, major New Source Review (NSR), and minor source NSR regulations address future new and modified SO
2
sources above major and minor permitting thresholds with the intent of ensuring that the SO
2
NAAQS will not be exceeded within or outside of the State because of new facility construction or existing facility modification within the State.

Based on this evaluation, as discussed further in the EPA's TSD for this proposed rulemaking, the Agency proposes to find that sources within Mississippi will not interfere with maintenance of the 2010 1-hour SO
2
NAAQS in any other State.

IV. Proposed Action

The EPA is proposing to approve Mississippi's January 27, 2022, prong 1 and prong 2 infrastructure SIP addressing interstate transport for the 2010 1-hour SO
2
NAAQS. Based on the EPA's WOE analysis, and as more thoroughly discussed in the TSD, the Agency proposes to determine that emissions from Mississippi will not contribute significantly to nonattainment in, or interfere with maintenance of, any other State with respect to the 2010 SO
2
NAAQS. The EPA therefore proposes to find that Mississippi's SIP contains adequate provisions consistent with CAA section 110(a)(2)(D)(i)(I).

V. Statutory and Executive Order Reviews

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations.
48

Thus, in reviewing SIP

submissions, the EPA's role is to approve State choices, provided that they meet the criteria of the CAA. Accordingly, this proposed rulemaking merely proposes to approve State law as meeting Federal requirements and does not impose additional requirements beyond those imposed by State law. For that reason, this proposed rulemaking:

48

See
42 U.S.C. 7410(k); 40 CFR 52.02(a).

• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);

• Is not an Executive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this action is not significant under Executive Order 12866;

• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501
et seq.
);

• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601
et seq.
);

• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);

• Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);

• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;

• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and

• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA.

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

List of Subjects in 40 CFR Part 52

Environmental protection, Air pollution control, Carbon monoxide, Incorporation by reference, Intergovernmental relations, Lead, Nitrogen dioxide, Ozone, Particulate matter, Reporting and recordkeeping requirements, Sulfur oxides, Volatile organic compounds.

(Authority: 42 U.S.C. 7401
et seq.
)

Dated: August 20, 2026.
Kristy Eubanks,
Deputy Regional Administrator performing the functions and duties of the Regional Administrator, Region 4.

[FR Doc. 2026-17503 Filed 8-26-26; 8:45 am]
BILLING CODE 6560-50-P

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2026-17503. Public record. Not legal advice.