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37 In deciding whether to invoke the exception by 

making and publishing a finding that an action is 

based on a determination of nationwide scope or 

effect, the Administrator takes into account a 

number of policy considerations, including his 

judgment balancing the benefit of obtaining the D.C. 

Circuit’s authoritative centralized review versus 

allowing development of the issue in other contexts 

and the best use of Agency resources. 

38A finding of nationwide scope or effect is also 

appropriate for actions that cover states in multiple 

judicial circuits. In the report on the 1977 

Amendments that revised section 307(b)(1) of the 

CAA, Congress noted that the Administrator’s 

determination that the ‘‘nationwide scope or effect’’ 

exception applies would be appropriate for any 

action that has a scope or effect beyond a single 

judicial circuit. See H.R. Rep. No. 95–294 at 323, 

324, reprinted in 1977 U.S.C.C.A.N. 1402–03. 

39The EPA may take a consolidated, single final 

action on all of the proposed SIP disapproval 

actions with respect to obligations under CAA 

section 110(a)(2)(D)(i)(I) for the 2015 ozone 

NAAQS. Should EPA take a single final action on 

all such disapprovals, this action would be 

nationally applicable, and the EPA would also 

anticipate, in the alternative, making and 

publishing a finding that such final action is based 

on a determination of nationwide scope or effect. 

not significantly or uniquely affect small 

governments. The action imposes no 

enforceable duty on any state, local or 

tribal governments or the private sector. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. It will not have substantial 

direct effects on the states, on the 

relationship between the national 

government and the states, or on the 

distribution of power and 

responsibilities among the various 

levels of government. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This action does not have tribal 

implications as specified in Executive 

Order 13175. This action does not apply 

on any Indian reservation land, any 

other area where the EPA or an Indian 

tribe has demonstrated that a tribe has 

jurisdiction, or non-reservation areas of 

Indian country. Thus, Executive Order 

13175 does not apply to this action. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

The EPA interprets Executive Order 

13045 as applying only to those 

regulatory actions that concern 

environmental health or safety risks that 

the EPA has reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive Order. This action is not 

subject to Executive Order 13045 

because it merely proposes to 

disapprove a SIP submission as not 

meeting the CAA. 

H. Executive Order 13211, Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

This action is not subject to Executive 

Order 13211, because it is not a 

significant regulatory action under 

Executive Order 12866. 

I. National Technology Transfer and 

Advancement Act 

This rulemaking does not involve 

technical standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

The EPA believes the human health or 

environmental risk addressed by this 

action will not have potential 

disproportionately high and adverse 

human health or environmental effects 

on minority, low-income or indigenous 

populations. This action merely 

proposes to disapprove a SIP 

submission as not meeting the CAA. 

K. CAA Section 307(b)(1) 

Section 307(b)(1) of the CAA governs 

judicial review of final actions by the 

EPA. This section provides, in part, that 

petitions for review must be filed in the 

D.C. Circuit: (i) When the agency action 

consists of ‘‘nationally applicable 

regulations promulgated, or final actions 

taken, by the Administrator,’’ or (ii) 

when such action is locally or regionally 

applicable, if ‘‘such action is based on 

a determination of nationwide scope or 

effect and if in taking such action the 

Administrator finds and publishes that 

such action is based on such a 

determination.’’ For locally or regionally 

applicable final actions, the CAA 

reserves to the EPA complete discretion 

whether to invoke the exception in 

(ii).37

If the EPA takes final action on this 

proposed rulemaking the Administrator 

intends to exercise the complete 

discretion afforded to him under the 

CAA to make and publish a finding that 

the final action (to the extent a court 

finds the action to be locally or 

regionally applicable) is based on a 

determination of ‘‘nationwide scope or 

effect’’ within the meaning of CAA 

section 307(b)(1). Through this 

rulemaking action (in conjunction with 

a series of related actions on other SIP 

submissions for the same CAA 

obligations), the EPA interprets and 

applies section 110(a)(2)(d)(i)(I) of the 

CAA for the 2015 ozone NAAQS based 

on a common core of nationwide policy 

judgments and technical analysis 

concerning the interstate transport of 

pollutants throughout the continental 

U.S. In particular, the EPA is applying 

here (and in other proposed actions 

related to the same obligations) the 

same, nationally consistent 4-step 

framework for assessing good neighbor 

obligations for the 2015 ozone NAAQS. 

The EPA relies on a single set of 

updated, 2016-base year photochemical 

grid modeling results of the year 2023 

as the primary basis for its assessment 

of air quality conditions and 

contributions at steps 1 and 2 of that 

framework. Further, the EPA proposes 

to determine and apply a set of 

nationally consistent policy judgments 

to apply the 4-step framework. The EPA 

has selected a nationally uniform 

analytic year (2023) for this analysis and 

is applying a nationally uniform 

approach to nonattainment and 

maintenance receptors and a nationally 

uniform approach to contribution 

threshold analysis.38 For these reasons, 

the Administrator intends, if this 

proposed action is finalized, to exercise 

the complete discretion afforded to him 

under the CAA to make and publish a 

finding that this action is based on one 

or more determinations of nationwide 

scope or effect for purposes of CAA 

section 307(b)(1).39

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Ozone. 

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

Dated: February 9, 2022. 

Meghan A. McCollister, 

Regional Administrator, Region 7. 

[FR Doc. 2022–03183 Filed 2–18–22; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R04–OAR–2021–0841; EPA–HQ– 

OAR–2021–0663; FRL–9421–01–R4] 

Air Plan Disapproval; AL, MS, TN; 

Interstate Transport Requirements for 

the 2015 8-Hour Ozone National 

Ambient Air Quality Standards 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule and withdrawal 

of proposed rule. 

SUMMARY: Pursuant to the Federal Clean 

Air Act (CAA or the Act), the 

Environmental Protection Agency (EPA 

or Agency) is proposing to disapprove 

State Implementation Plan (SIP) 

submittals from Alabama, Mississippi, 


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1National Ambient Air Quality Standards for 

Ozone, Final Rule, 80 FR 65292 (October 26, 2015). 

Although the level of the standard is specified in 

the units of ppm, ozone concentrations are also 

described in parts per billion (ppb). For example, 

0.070 ppm is equivalent to 70 ppb. 

2SIP revisions that are intended to meet the 

applicable requirements of section 110(a)(1) and (2) 

of the CAA are often referred to as infrastructure 

SIPs and the applicable elements under section 

110(a)(2) are referred to as infrastructure 

requirements. 

and Tennessee regarding the interstate 

transport requirements for the 2015 8- 

hour ozone national ambient air quality 

standards (NAAQS or standard). The 

‘‘Good Neighbor’’ or ‘‘Interstate 

Transport’’ provision requires that each 

state’s implementation plan contain 

adequate provisions to prohibit 

emissions from within the state from 

significantly contributing to 

nonattainment or interfering with 

maintenance of the NAAQS in other 

states. This requirement is part of the 

broader set of ‘‘infrastructure’’ 

requirements, which are designed to 

ensure that the structural components of 

each state’s air quality management 

program are adequate to meet the state’s 

responsibilities under the CAA. These 

disapprovals, if finalized, will establish 

a 2-year deadline for EPA to promulgate 

a Federal Implementation Plan (FIP) to 

address the relevant interstate transport 

requirements, unless EPA approves a 

subsequent SIP submittal that meets 

these requirements. Disapproval does 

not start a mandatory sanctions clock. 

DATES: Comments. Comments on this 

proposed rule must be received on or 

before April 25, 2022. 

Withdrawal: As of February 22, 2022, 

the proposed rule published December 

30, 2019, at 84 FR 71854, is withdrawn. 

ADDRESSES: You may submit comments, 

identified by Docket No. EPA–R04– 

OAR–2021–0841, through the Federal 

eRulemaking Portal at https://

www.regulations.gov following the 

online instructions for submitting 

comments. 

Instructions: All submissions received 

must include the Docket No. EPA–R04– 

OAR–2021–0841 for this rulemaking. 

Comments received may be posted 

without change to https://

www.regulations.gov/, including any 

personal information provided. For 

detailed instructions on submitting 

comments and additional information 

on the rulemaking process, see the 

‘‘Public Participation’’ heading of the 

SUPPLEMENTARY INFORMATION section of 

this document. Out of an abundance of 

caution for members of the public and 

staff, the EPA Docket Center and 

Reading Room are open to the public by 

appointment only to reduce the risk of 

transmitting COVID–19. The Docket 

Center staff also continues to provide 

remote customer service via email, 

phone, and webform. For further 

information on EPA Docket Center 

services and the current status, please 

visit EPA online at https://

www.epa.gov/dockets. 

FOR FURTHER INFORMATION CONTACT: 

Evan Adams of the Air Regulatory 

Management 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. 

Mr. Adams can be reached by telephone 

at (404) 562–9009, or via electronic mail 

at adams.evan@epa.gov. 

SUPPLEMENTARY INFORMATION: Public 

Participation: Submit your comments, 

identified by Docket No. EPA–R04– 

OAR–2021–0841, at https://

www.regulations.gov. Once submitted, 

comments cannot be edited or removed 

from the docket. EPA may publish any 

comment received to its public docket. 

Do not submit to EPA’s docket at 

https://www.regulations.gov 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. 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). 

There are two dockets supporting this 

action, EPA–R04–OAR–2021–0841 and 

EPA–HQ–OAR–2021–0663. Docket No. 

EPA–R04–OAR–2021–0841 contains 

information specific to Alabama, 

Mississippi, and Tennessee, including 

this notice of proposed rulemaking. 

Docket No. EPA–HQ–OAR–2021–0663 

contains additional modeling files, 

emissions inventory files, technical 

support documents, and other relevant 

supporting documentation regarding 

interstate transport of emissions for the 

2015 8-hour ozone NAAQS which are 

being used to support this action. All 

comments regarding information in 

either of these dockets are to be made 

in Docket No. EPA–R04–OAR–2021– 

0841. For 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-epadockets. Due to public health concerns 

related to COVID–19, the EPA Docket 

Center and Reading Room are open to 

the public by appointment only. The 

Docket Center staff also continues to 

provide remote customer service via 

email, phone, and webform. For further 

information and updates on EPA Docket 

Center services, please visit EPA online 

at https://www.epa.gov/dockets. 

EPA continues to carefully and 

continuously monitor information from 

the Centers for Disease Control and 

Prevention (CDC), local area health 

departments, and Federal partners so 

that EPA can respond rapidly as 

conditions change regarding COVID–19. 

The indices to Docket No. EPA–R04– 

OAR–2021–0841 and Docket No. EPA– 

R04–OAR–2021–0841 are available 

electronically at www.regulations.gov. 

While all documents in each docket are 

listed in their respective index, some 

information may not be publicly 

available due to docket file size 

restrictions or content (e.g., CBI). 

Table of Contents 

I. Background 

A. Description of Statutory Background 

B. Description of EPA’s Four Step 

Interstate Transport Regulatory Process 

C. Background on EPA’s Ozone Transport 

Modeling Information 

D. EPA’s Approach To Evaluating 

Interstate Transport SIPs for the 2015 8- 

hour Ozone NAAQS 

II. SIP Submissions and EPA’s Evaluation 

A. Alabama 

B. Mississippi 

C. Tennessee 

III. Proposed Actions 

IV. Statutory and Executive Order Reviews 

I. Background 

The following provides background 

for EPA’s proposed actions related to 

the interstate transport requirements for 

the 2015 8-hour ozone NAAQS for the 

states of Alabama, Mississippi, and 

Tennessee. 

A. Description of Statutory Background 

On October 1, 2015, EPA promulgated 

a revision to the ozone NAAQS (2015 8- 

hour ozone NAAQS), lowering the level 

of both the primary and secondary 

standards to 0.070 parts per million 

(ppm).1 Section 110(a)(1) of the CAA 

requires states to submit, within 3 years 

after promulgation of a new or revised 

standard, SIP submissions meeting the 

applicable requirements of section 

110(a)(2).2 One of these applicable 

requirements is found in CAA section 

110(a)(2)(D)(i)(I), otherwise known as 

the ‘‘good neighbor’’ or ‘‘interstate 

transport’’ provision, which generally 

requires SIPs to contain adequate 

provisions to prohibit in-state emissions 

activities from having certain adverse 

air quality effects on other states due to 


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3See North Carolina v. EPA, 531 F.3d 896, 909– 

11 (D.C. Cir. 2008). 

4See Federal Implementation Plans: Interstate 

Transport of Fine Particulate Matter and Ozone and 

Correction of SIP Approvals, 76 FR 48208 (August 

8, 2011). 

5Cross-State Air Pollution Rule Update for the 

2008 Ozone NAAQS, 81 FR 74504 (October 26, 

2016). 

6 In 2019, the United States Court of Appeals for 

the District of Columbia Circuit (D.C. Circuit) 

remanded CSAPR Update to the extent it failed to 

require upwind states to eliminate their significant 

contribution by the next applicable attainment date 

by which downwind states must come into 

compliance with the NAAQS, as established under 

CAA section 181(a). Wisconsin v. EPA, 938 F.3d 

303, 313 (D.C. Cir. 2019). The Revised CSAPR 

Update for the 2008 Ozone NAAQS, 86 FR 23054 

(April 30, 2021), responded to the remand of 

CSAPR Update in Wisconsin and the vacatur of a 

separate rule, the ‘‘CSAPR Close-Out,’’ 83 FR 65878 

(December 21, 2018), in New York v. EPA, 781 F. 

App’x. 4 (D.C. Cir. 2019). 

7 In addition to CSAPR rulemakings, other 

regional rulemakings addressing ozone transport 

include the ‘‘NOX SIP Call,’’ 63 FR 57356 (October 

27, 1998), and the ‘‘Clean Air Interstate Rule’’ 

(CAIR), 70 FR 25162 (May 12, 2005). 

8See Notice of Availability of the Environmental 

Protection Agency’s Preliminary Interstate Ozone 

Transport Modeling Data for the 2015 8-hour Ozone 

National Ambient Air Quality Standard (NAAQS), 

82 FR 1733 (January 6, 2017). 

9See 82 FR 1733, 1735 (January 6, 2017). 

10See Information on the Interstate Transport 

State Implementation Plan Submissions for the 

2008 Ozone National Ambient Air Quality 

Standards under Clean Air Act Section 

110(a)(2)(D)(i)(I), October 27, 2017 (‘‘October 2017 

memorandum’’), available in Docket No. EPA–HQ– 

OAR–2021–0663 or at https://www.epa.gov/ 

interstate-air-pollution-transport/interstate-airpollution-transport-memos-and-notices. 

11See Information on the Interstate Transport 

State Implementation Plan Submissions for the 

2015 Ozone National Ambient Air Quality 

Standards under Clean Air Act Section 

110(a)(2)(D)(i)(I), March 27, 2018 (‘‘March 2018 

memorandum’’), available in Docket No. EPA–HQ– 

OAR–2021–0663 or at https://www.epa.gov/ 

interstate-air-pollution-transport/interstate-airpollution-transport-memos-and-notices. 

12The March 2018 memorandum, however, 

provided, ‘‘While the information in this 

memorandum and the associated air quality 

analysis data could be used to inform the 

development of these SIPs, the information is not 

a final determination regarding states’ obligations 

under the good neighbor provision. Any such 

determination would be made through notice-andcomment rulemaking.’’ 

interstate transport of pollution. There 

are two so-called ‘‘prongs’’ within CAA 

section 110(a)(2)(D)(i)(I). A SIP for a 

new or revised NAAQS must contain 

adequate provisions prohibiting any 

source or other type of emissions 

activity within the state from emitting 

air pollutants in amounts that will 

significantly contribute to 

nonattainment of the NAAQS in another 

state (prong 1) or interfere with 

maintenance of the NAAQS in another 

state (prong 2). EPA and states must give 

independent significance to prong 1 and 

prong 2 when evaluating downwind air 

quality problems under CAA section 

110(a)(2)(D)(i)(I).3

B. Description of EPA’s Four Step 

Interstate Transport Regulatory Process 

EPA is using the 4-step interstate 

transport framework (or 4-step 

framework) to evaluate the states’ 

implementation plan submittals 

addressing the interstate transport 

provision for the 2015 8-hour ozone 

NAAQS. EPA has addressed the 

interstate transport requirements of 

CAA section 110(a)(2)(D)(i)(I) with 

respect to prior ozone NAAQS in 

several regional regulatory actions, 

including the Cross-State Air Pollution 

Rule (CSAPR), which addressed 

interstate transport with respect to the 

1997 ozone NAAQS as well as the 1997 

and 2006 fine particulate matter 

standards,4 the Cross-State Air Pollution 

Rule Update (CSAPR Update) 5 and the 

Revised CSAPR Update, both of which 

addressed the 2008 ozone NAAQS.6

Through the development and 

implementation of the CSAPR 

rulemakings and prior regional 

rulemakings pursuant to the interstate 

transport provision,7 EPA, working in 

partnership with states, developed the 

following 4-step interstate transport 

framework to evaluate a state’s 

obligations to eliminate interstate 

transport emissions under the interstate 

transport provision for the ozone 

NAAQS: (1) Identify monitoring sites 

that are projected to have problems 

attaining and/or maintaining the 

NAAQS (i.e., nonattainment and/or 

maintenance receptors); (2) identify 

states that impact those air quality 

problems in other (i.e., downwind) 

states sufficiently such that the states 

are considered ‘‘linked’’ and therefore 

warrant further review and analysis; (3) 

identify the emissions reductions 

necessary (if any), applying a 

multifactor analysis, to eliminate each 

linked upwind state’s significant 

contribution to nonattainment or 

interference with maintenance of the 

NAAQS at the locations identified in 

Step 1; and (4) adopt permanent and 

enforceable measures needed to achieve 

those emissions reductions. 

C. Background on EPA’s Ozone 

Transport Modeling Information 

In general, EPA has performed 

nationwide air quality modeling to 

project ozone design values which are 

used in combination with measured 

data to identify nonattainment and 

maintenance receptors. To quantify the 

contribution of emissions from specific 

upwind states on 2023 ozone design 

values for the identified downwind 

nonattainment and maintenance 

receptors, EPA performed nationwide, 

state-level ozone source apportionment 

modeling for 2023. The source 

apportionment modeling provided 

contributions to ozone at receptors from 

precursor emissions of anthropogenic 

nitrogen oxides (NOX) and volatile 

organic compounds (VOCs) in 

individual upwind states. 

EPA has released several documents 

containing projected design values, 

contributions, and information relevant 

to evaluating interstate transport with 

respect to the 2015 8-hour ozone 

NAAQS. First, on January 6, 2017, EPA 

published a notice of data availability 

(NODA) in which the Agency requested 

comment on preliminary interstate 

ozone transport data including projected 

ozone design values and interstate 

contributions for 2023 using a 2011 base 

year platform.8 In the NODA, EPA used 

the year 2023 as the analytic year for 

this preliminary modeling because that 

year aligns with the expected attainment 

year for Moderate ozone nonattainment 

areas for the 2015 8-hour ozone 

NAAQS.9 On October 27, 2017, EPA 

released a memorandum (October 2017 

memorandum) containing updated 

modeling data for 2023, which 

incorporated changes made in response 

to comments on the NODA, and noted 

that the modeling may be useful for 

states developing SIPs to address 

interstate transport obligations for the 

2008 ozone NAAQS.10 On March 27, 

2018, EPA issued a memorandum 

(March 2018 memorandum) noting that 

the same 2023 modeling data released in 

the October 2017 memorandum could 

also be useful for identifying potential 

downwind air quality problems with 

respect to the 2015 8-hour ozone 

NAAQS at Step 1 of the 4-step interstate 

transport framework.11 The March 2018 

memorandum also included the then 

newly available contribution modeling 

data for 2023 to assist states in 

evaluating their impact on potential 

downwind air quality problems for the 

2015 8-hour ozone NAAQS under Step 

2 of the 4-step interstate transport 

framework.12 EPA subsequently issued 

two more memoranda in August and 

October 2018, providing additional 

information to states developing 

interstate transport SIP submissions for 

the 2015 8-hour ozone NAAQS 

concerning, respectively, potential 

contribution thresholds that may be 

appropriate to apply in Step 2 of the 4- 

step interstate transport framework, and 

considerations for identifying 

downwind areas that may have 

problems maintaining the standard at 


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13See Analysis of Contribution Thresholds for 

Use in Clean Air Act Section 110(a)(2)(D)(i)(I) 

Interstate Transport State Implementation Plan 

Submissions for the 2015 Ozone National Ambient 

Air Quality Standards, August 31, 2018) (‘‘August 

2018 memorandum’’), and Considerations for 

Identifying Maintenance Receptors for Use in Clean 

Air Act Section 110(a)(2)(D)(i)(I) Interstate 

Transport State Implementation Plan Submissions 

for the 2015 Ozone National Ambient Air Quality 

Standards, October 19, 2018 (‘‘October 2018 

memorandum’’), available in Docket No. EPA–HQ– 

OAR–2021–0663 or at https://www.epa.gov/ 

airmarkets/memo-and-supplemental-informationregarding-interstate-transport-sips-2015-ozonenaaqs. 

14The results of this modeling, as well as the 

underlying modeling files, are included in Docket 

No. EPA–HQ–OAR–2021–0663. 

15See 85 FR 68964, 68981 (October 30, 2020). 

16See the Air Quality Modeling Technical 

Support Document for the Final Revised Cross-State 

Air Pollution Rule Update, included in Docket No. 

EPA–HQ–OAR–2021–0663. 

17Additional details and documentation related 

to the MOVES3 model can be found at https://

www.epa.gov/moves/latest-version-motor-vehicleemission-simulator-moves. 

18Ramboll Environment and Health, January 

2021, www.camx.com. 

19March 2018 memorandum, Attachment A. 

20 Id. at A–1. 

Step 1 of the 4-step interstate transport 

framework.13

Since the release of the modeling data 

shared in the March 2018 

memorandum, EPA performed updated 

modeling using a 2016-based emissions 

modeling platform (i.e., 2016v1). This 

emissions platform was developed 

under the EPA/Multi-Jurisdictional 

Organization (MJO)/state collaborative 

project.14 This collaborative project was 

a multi-year joint effort by EPA, MJOs, 

and states to develop a new, more recent 

emissions platform for use by EPA and 

states in regulatory modeling as an 

improvement over the dated 2011-based 

platform that EPA had used to project 

ozone design values and contribution 

data provided in the 2017 and 2018 

memoranda. EPA used the 2016v1 

emissions to project ozone design values 

and contributions for 2023. On October 

30, 2020, in the Notice of Proposed 

Rulemaking for the Revised CSAPR 

Update, EPA released and accepted 

public comment on 2023 modeling that 

used the 2016v1 emissions platform.15

Although the Revised CSAPR Update 

addressed transport for the 2008 ozone 

NAAQS, the projected design values 

and contributions from the 2016v1 

platform are also useful for identifying 

downwind ozone problems and linkages 

with respect to the 2015 8-hour ozone 

NAAQS.16

Following the Revised CSAPR Update 

final rule, EPA made further updates to 

the 2016 emissions platform to include 

mobile emissions from EPA’s Motor 

Vehicle Emission Simulator (MOVES) 

model 17 and updated emissions 

projections for electric generating units 

(EGUs) that reflect the emissions 

reductions from the Revised CSAPR 

Update, recent information on plant 

closures, and other sector trends. The 

construct of the updated emissions 

platform, 2016v2, is described in the 

Preparation of Emissions Inventories for 

the 2016v2 North American Emissions 

Modeling Platform technical support 

document (TSD) for this proposed rule 

and is included in Docket No. EPA–HQ– 

OAR–2021–0663. EPA performed air 

quality modeling of the 2016v2 

emissions using the most recent public 

release version of the Comprehensive 

Air Quality Modeling with Extensions 

(CAMx) photochemical modeling, 

version 7.10.18 EPA proposes to 

primarily rely on modeling based on the 

updated and newly available 2016v2 

emissions platform in evaluating these 

submissions with respect to Steps 1 and 

2 of the 4-step interstate transport 

framework. By using the updated 

modeling results, EPA is using the most 

current and technically appropriate 

information for this proposed 

rulemaking. Section II of this notice and 

the Air Quality Modeling TSD included 

in Docket No. EPA–HQ–OAR–2021– 

0663 for this proposal contain 

additional detail on the modeling 

performed using the 2016v2 emissions 

modeling. 

In this notice, EPA is accepting public 

comment on this updated 2023 

modeling, which uses the 2016v2 

emissions platform. Details on the air 

quality modeling and the methods for 

projecting design values and 

determining contributions in 2023 are 

described in the Air Quality Modeling 

TSD for 2015 8-hour ozone NAAQS 

Transport SIP Proposed Actions. 

Comments on EPA’s air quality 

modeling should be submitted in Docket 

No. EPA–R04–OAR–2021–0841. 

Comments are not being accepted in 

Docket No. EPA–HQ–OAR–2021–0663. 

States may have chosen to rely on the 

results of EPA modeling and/or 

alternative modeling performed by 

states or Multi-Jurisdictional 

Organizations (MJOs) to evaluate 

downwind air quality problems and 

contributions as part of their 

submissions. In Section II, EPA 

evaluates how Alabama, Mississippi, 

and Tennessee used air quality 

modeling information in their 

submissions. 

D. EPA’s Approach to Evaluating 

Interstate Transport SIPs for the 2015 8- 

Hour Ozone NAAQS 

EPA proposes to apply a consistent 

set of policy judgments across all states 

for purposes of evaluating interstate 

transport obligations and the 

approvability of interstate transport SIP 

submittals for the 2015 8-hour ozone 

NAAQS. These policy judgments reflect 

consistency with relevant case law and 

past agency practice as reflected in 

CSAPR and related rulemakings. 

Nationwide consistency in approach is 

particularly important in the context of 

interstate ozone transport, which is a 

regional-scale pollution problem 

involving many smaller contributors. 

Effective policy solutions to the problem 

of interstate ozone transport going back 

to the NOx SIP Call have necessitated 

the application of a uniform framework 

of policy judgments in order to ensure 

an ‘‘efficient and equitable’’ approach. 

See EME Homer City Generation, LP v. 

EPA, 572 U.S. 489, 519 (2014). 

In the March, August, and October 

2018 memoranda, EPA recognized that 

states may be able to establish 

alternative approaches to addressing 

their interstate transport obligations for 

the 2015 8-hour ozone NAAQS that vary 

from a nationally uniform framework. 

EPA emphasized in these memoranda, 

however, that such alternative 

approaches must be technically justified 

and appropriate in light of the facts and 

circumstances of each particular state’s 

submittal. In general, EPA continues to 

believe that deviation from a nationally 

consistent approach to ozone transport 

must be substantially justified and have 

a well-documented technical basis that 

is consistent with relevant case law. 

Where states submitted SIPs that rely on 

any such potential concepts as may 

have been identified or suggested in the 

past, EPA will evaluate whether the 

state adequately justified the technical 

and legal basis for doing so. 

EPA notes that certain potential 

concepts included in an attachment to 

the March 2018 memorandum require 

unique consideration, and these ideas 

do not constitute agency guidance with 

respect to transport obligations for the 

2015 8-hour ozone NAAQS. Attachment 

A to the March 2018 memorandum 

identified a ‘‘Preliminary List of 

Potential Flexibilities’’ that could 

potentially inform SIP development.19

However, EPA made clear in that 

attachment that the list of ideas were 

not suggestions endorsed by the Agency 

but rather ‘‘comments provided in 

various forums’’ on which EPA sought 

‘‘feedback from interested 

stakeholders.’’ 20 Further, Attachment A 

stated, ‘‘EPA is not at this time making 

any determination that the ideas 

discussed below are consistent with the 

requirements of the CAA, nor is EPA 

specifically recommending that states 


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21 Id. 

22For attainment dates for the 2015 8-hour ozone 

NAAQS, refer to CAA section 181(a), 40 CFR 

51.1303, and Additional Air Quality Designations 

for the 2015 Ozone National Ambient Air Quality 

Standards, 83 FR 25776 (June 4, 2018, effective 

August 3, 2018). 

23EPA notes that the court in Maryland did not 

have occasion to evaluate circumstances in which 

EPA may determine that an upwind linkage to a 

downwind air quality problem exists at Steps 1 and 

2 of the interstate transport framework by a 

particular attainment date, but for reasons of 

impossibility or profound uncertainty the Agency is 

unable to mandate upwind pollution controls by 

that date. See Wisconsin, 938 F.3d at 320. The D.C. 

Circuit noted in Wisconsin that upon a sufficient 

showing, these circumstances may warrant 

flexibility in effectuating the purpose of the 

interstate transport provision. 

24See CAA section 181(a); 40 CFR 51.1303; 

Additional Air Quality Designations for the 2015 

Ozone National Ambient Air Quality Standards, 83 

FR 25776 (June 4, 2018, effective August 3, 2018). 

25See North Carolina v. EPA, 531 F.3d 896, 910– 

11 (D.C. Cir. 2008) (holding that EPA must give 

‘‘independent significance’’ to each prong of CAA 

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

26See 81 FR 74504 (October 26, 2016). This same 

concept, relying on both current monitoring data 

and modeling to define nonattainment receptor, 

was also applied in CAIR. See 70 FR at 25241, 

25249 (January 14, 2005); see also North Carolina, 

531 F.3d at 913–14 (affirming as reasonable EPA’s 

approach to defining nonattainment in CAIR). 

use these approaches.’’ 21 Attachment A 

to the March 2018 memorandum, 

therefore, does not constitute agency 

guidance, but was intended to generate 

further discussion around potential 

approaches to addressing ozone 

transport among interested stakeholders. 

To the extent states sought to develop or 

rely on these ideas in support of their 

SIP submittals, EPA will thoroughly 

review the technical and legal 

justifications for doing so. 

The remainder of this section 

describes the EPA’s proposed 

framework with respect to analytic year, 

definition of nonattainment and 

maintenance receptors, selection of 

contribution threshold, and multifactor 

control strategy assessment. 

1. Selection of Analytic Year 

In general, the states and EPA must 

implement the interstate transport 

provision in a manner ‘‘consistent with 

the provisions of [title I of the CAA.]’’ 

See CAA section 110(a)(2)(D)(i). This 

requires, among other things, that these 

obligations are addressed consistently 

with the timeframes for downwind areas 

to meet their CAA obligations. With 

respect to ozone NAAQS, under CAA 

section 181(a), this means obligations 

must be addressed ‘‘as expeditiously as 

practicable’’ and no later than the 

schedule of attainment dates provided 

in CAA section 181(a)(1).22 Several D.C. 

Circuit court decisions address the issue 

of the relevant analytic year for the 

purposes of evaluating ozone transport 

air-quality problems. On September 13, 

2019, the D.C. Circuit issued a decision 

in Wisconsin v. EPA, remanding the 

CSAPR Update to the extent that it 

failed to require upwind states to 

eliminate their significant contribution 

by the next applicable attainment date 

by which downwind states must come 

into compliance with the NAAQS, as 

established under CAA section 181(a). 

See 938 F.3d 303, 313. 

On May 19, 2020, the D.C. Circuit 

issued a decision in Maryland v. EPA 

that cited the Wisconsin decision in 

holding that EPA must assess the impact 

of interstate transport on air quality at 

the next downwind attainment date, 

including Marginal area attainment 

dates, in evaluating the basis for EPA’s 

denial of a petition under CAA section 

126(b). Maryland v. EPA, 958 F.3d 1185, 

1203–04 (D.C. Cir. 2020). The court 

noted that ‘‘section 126(b) incorporates 

the Good Neighbor Provision,’’ and, 

therefore, ‘‘EPA must find a violation [of 

section 126] if an upwind source will 

significantly contribute to downwind 

nonattainment at the next downwind 

attainment deadline. Therefore, the 

agency must evaluate downwind air 

quality at that deadline, not at some 

later date.’’ Id. at 1204 (emphasis 

added). EPA interprets the court’s 

holding in Maryland as requiring the 

states and the Agency, under the good 

neighbor provision, to assess downwind 

air quality as expeditiously as 

practicable and no later than the next 

applicable attainment date,23 which is 

now the Moderate area attainment date 

under CAA section 181 for ozone 

nonattainment. The Moderate area 

attainment date for the 2015 8-hour 

ozone NAAQS is August 3, 2024.24 EPA 

believes that 2023 is now the 

appropriate year for analysis of 

interstate transport obligations for the 

2015 8-hour ozone NAAQS, because the 

2023 ozone season is the last relevant 

ozone season during which achieved 

emissions reductions in linked upwind 

states could assist downwind states 

with meeting the August 3, 2024, 

Moderate area attainment date for the 

2015 8-hour ozone NAAQS. 

EPA recognizes that the attainment 

date for nonattainment areas classified 

as Marginal for the 2015 8-hour ozone 

NAAQS was August 3, 2021. Under the 

Maryland holding, any necessary 

emissions reductions to satisfy interstate 

transport obligations should have been 

implemented by no later than this date. 

At the time of the statutory deadline to 

submit interstate transport SIPs (October 

1, 2018), many states relied upon EPA 

modeling of the year 2023, and no state 

provided an alternative analysis using a 

2021 analytic year (or the prior 2020 

ozone season). However, EPA must act 

on SIP submittals using the information 

available at the time it takes such action. 

In this circumstance, EPA does not 

believe it would be appropriate to 

evaluate states’ obligations under CAA 

section 110(a)(2)(D)(i)(I) as of an 

attainment date that is wholly in the 

past, because the Agency interprets the 

interstate transport provision as forward 

looking. See 86 FR 23054, 23074; see 

also Wisconsin, 938 F.3d at 322. 

Consequently, in this proposal EPA will 

use the analytical year of 2023 to 

evaluate each state’s CAA section 

110(a)(2)(D)(i)(I) SIP submission with 

respect to the 2015 8-hour ozone 

NAAQS. 

2. Step 1 of the 4-Step Interstate 

Transport Framework 

In Step 1, EPA identifies monitoring 

sites that are projected to have problems 

attaining and/or maintaining the 

NAAQS in the 2023 analytic year. 

Where EPA’s analysis shows that a site 

does not fall under the definition of a 

nonattainment or maintenance receptor, 

that site is excluded from further 

analysis under EPA’s 4-step interstate 

transport framework. For sites that are 

identified as a nonattainment or 

maintenance receptor in 2023, EPA 

proceeds to the next step of the 4-step 

interstate transport framework by 

identifying the upwind state’s 

contribution to those receptors. 

EPA’s approach to identifying ozone 

nonattainment and maintenance 

receptors in this action is consistent 

with the approach used in previous 

transport rulemakings. EPA’s approach 

gives independent consideration to both 

the ‘‘contribute significantly to 

nonattainment’’ and the ‘‘interfere with 

maintenance’’ prongs of CAA section 

110(a)(2)(D)(i)(I), consistent with the 

D.C. Circuit’s direction in North 

Carolina v. EPA.25

For the purpose of this proposal, EPA 

identifies nonattainment receptors as 

those monitoring sites that are projected 

to have average design values that 

exceed the NAAQS and that are also 

measuring nonattainment based on the 

most recent monitored design values. 

This approach is consistent with prior 

transport rulemakings, such as the 

CSAPR Update, where EPA defined 

nonattainment receptors as those areas 

that both currently measure 

nonattainment and that EPA projects 

will be in nonattainment in the future 

analytic year (i.e., 2023).26

In addition, in this proposal, EPA 

identifies a receptor to be a 

‘‘maintenance’’ receptor for purposes of 


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27See 76 FR 48208 (August 8, 2011). The CSAPR 

Update and Revised CSAPR Update also used this 

approach. See 81 FR 74504 (October 26, 2016) and 

86 FR 23054 (April 30, 2021). 28See August 2018 memorandum at 4. 

defining interference with maintenance, 

consistent with the method used in 

CSAPR and upheld by the D.C. Circuit 

in EME Homer City Generation, L.P. v. 

EPA, 795 F.3d 118, 136 (D.C. Cir. 

2015).27 Specifically, EPA identified 

maintenance receptors as those 

receptors that would have difficulty 

maintaining the relevant NAAQS in a 

scenario that takes into account 

historical variability in air quality at 

that receptor. The variability in air 

quality was determined by evaluating 

the ‘‘maximum’’ future design value at 

each receptor based on a projection of 

the maximum measured design value 

over the relevant period. EPA interprets 

the projected maximum future design 

value to be a potential future air quality 

outcome consistent with the 

meteorology that yielded maximum 

measured concentrations in the ambient 

data set analyzed for that receptor (i.e., 

ozone conducive meteorology). EPA 

also recognizes that previously 

experienced meteorological conditions 

(e.g., dominant wind direction, 

temperatures, air mass patterns) 

promoting ozone formation that led to 

maximum concentrations in the 

measured data may reoccur in the 

future. The maximum design value 

gives a reasonable projection of future 

air quality at the receptor under a 

scenario in which such conditions do, 

in fact, reoccur. The projected 

maximum design value is used to 

identify upwind emissions that, under 

those circumstances, could interfere 

with the downwind area’s ability to 

maintain the NAAQS. 

Recognizing that nonattainment 

receptors are also, by definition, 

maintenance receptors, the EPA often 

uses the term ‘‘maintenance-only’’ to 

refer to those receptors that are not 

nonattainment receptors. Consistent 

with the concepts for maintenance 

receptors, as described above, the EPA 

identifies ‘‘maintenance-only’’ receptors 

as those monitoring sites that have 

projected average design values above 

the level of the applicable NAAQS, but 

that are not currently measuring 

nonattainment based on the most recent 

official design values. In addition, those 

monitoring sites with projected average 

design values below the NAAQS, but 

with projected maximum design values 

above the NAAQS are also identified as 

‘‘maintenance-only’’ receptors, even if 

they are currently measuring 

nonattainment based on the most recent 

official design values. 

3. Step 2 of the 4-Step Interstate 

Transport Framework 

In Step 2, EPA quantifies the 

contribution of each upwind state to 

each receptor in the 2023 analytic year. 

The contribution metric used in Step 2 

is defined as the average impact from 

each state to each receptor on the days 

with the highest ozone concentrations at 

the receptor based on the 2023 

modeling. If a state’s contribution value 

does not equal or exceed the threshold 

of 1 percent of the NAAQS (i.e., 0.70 

ppb for the 2015 8-hour ozone NAAQS), 

the upwind state is not ‘‘linked’’ to a 

downwind air quality problem, and 

EPA, therefore, concludes that the state 

does not significantly contribute to 

nonattainment or interfere with 

maintenance of the NAAQS in the 

downwind states. However, if a state’s 

contribution equals or exceeds the 1 

percent threshold, the state’s emissions 

are further evaluated in Step 3, 

considering both air quality and cost as 

part of a multi-factor analysis, to 

determine what, if any, emissions might 

be deemed ‘‘significant’’ and, thus, must 

be eliminated under CAA section 

110(a)(2)(D)(i)(I). 

EPA is proposing to rely in the first 

instance on the 1 percent threshold for 

the purpose of evaluating a state’s 

contribution to nonattainment or 

maintenance of the 2015 8-hour ozone 

NAAQS (i.e., 0.70 ppb) at downwind 

receptors. This is consistent with the 

Step 2 approach that EPA applied in 

CSAPR for the 1997 ozone NAAQS, 

which has subsequently been applied in 

the CSAPR Update when evaluating 

interstate transport obligations for the 

2008 ozone NAAQS. EPA continues to 

find 1 percent to be an appropriate 

threshold. For ozone, as EPA found in 

the CAIR, CSAPR, and CSAPR Update, 

a portion of the nonattainment problems 

from anthropogenic sources in the U.S. 

result from the combined impact of 

relatively small contributions from 

many upwind states, along with 

contributions from in-state sources and, 

in some cases, substantially larger 

contributions from a subset of particular 

upwind states. EPA’s analysis shows 

that much of the ozone transport 

problem being analyzed in this 

proposed rule is still the result of the 

collective impacts of contributions from 

many upwind states. Therefore, 

application of a consistent contribution 

threshold is necessary to identify those 

upwind states that should have 

responsibility for addressing their 

contribution to the downwind 

nonattainment and maintenance 

problems to which they collectively 

contribute. Continuing to use 1 percent 

of the NAAQS as the screening metric 

to evaluate collective contribution from 

many upwind states also allows EPA 

(and states) to apply a consistent 

framework to evaluate interstate 

emissions transport under the interstate 

transport provision from one NAAQS to 

the next. See 81 FR at 74518; see also 

86 FR at 23085 (reviewing and 

explaining rationale from CSAPR, 76 FR 

at 48237–38, for selection of 1 percent 

threshold). 

(a) EPA’s Experience With Alternative 

Step 2 Thresholds 

EPA’s August 2018 memorandum 

recognized that in certain 

circumstances, a state may be able to 

establish that an alternative contribution 

threshold of 1 ppb is justifiable. Where 

a state relies on this alternative 

threshold, and where that state 

determined that it was not linked at 

Step 2 using the alternative threshold, 

EPA will evaluate whether the state 

provided a technically sound 

assessment of the appropriateness of 

using this alternative threshold based on 

the facts and circumstances underlying 

its application in the particular SIP 

submission. 

EPA here shares further evaluation of 

its experience since the issuance of the 

August 2018 memorandum regarding 

use of alternative thresholds at Step 2. 

This experience leads the Agency to 

now believe it may not be appropriate 

to continue to attempt to recognize 

alternative contribution thresholds at 

Step 2. The August 2018 memorandum 

stated that ‘‘it may be reasonable and 

appropriate’’ for states to rely on an 

alternative threshold of 1 ppb threshold 

at Step 2.28 (The memorandum also 

indicated that any higher alternative 

threshold, such as 2 ppb, would likely 

not be appropriate.) However, EPA also 

provided that ‘‘air agencies should 

consider whether the recommendations 

in this guidance are appropriate for each 

situation.’’ Following receipt and review 

of 49 good neighbor SIP submittals for 

the 2015 8-hour ozone NAAQS, EPA’s 

experience has been that nearly every 

state that attempted to rely on a 1 ppb 

threshold did not provide sufficient 

information and analysis to support a 

determination that an alternative 

threshold was reasonable or appropriate 

for that state. 

For instance, in nearly all submittals, 

the states did not provide EPA with 

analysis specific to their state or the 

receptors to which its emissions are 

potentially linked. In one case, the 

proposed approval of Iowa’s SIP 

submittal, EPA expended its own 


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29Air Plan Approval; Iowa; Infrastructure State 

Implementation Plan Requirements for the 2015 

Ozone National Ambient Air Quality Standard, 85 

FR 12232 (March 2, 2020). The Agency received 

adverse comment on this proposed approval and 

has not taken final action with respect to this 

proposal. 

30EPA notes that Congress has placed on EPA a 

general obligation to ensure the requirements of the 

CAA are implemented consistently across states 

and regions. See CAA section 301(a)(2). Where the 

management and regulation of interstate pollution 

levels spanning many states is at stake, consistency 

in application of CAA requirements is paramount. 31See August 2018 memorandum at 4. 

resources to attempt to supplement the 

information submitted by the state, in 

order to more thoroughly evaluate the 

state-specific circumstances that could 

support approval.29 It was at EPA’s sole 

discretion to perform this analysis in 

support of the state’s submittal, and the 

Agency is not obligated to conduct 

supplemental analysis to fill the gaps 

whenever it believes a state’s analysis is 

insufficient. The Agency no longer 

intends to undertake supplemental 

analysis of SIP submittals with respect 

to alternative thresholds at Step 2 for 

purposes of the 2015 8-hour ozone 

NAAQS. 

Furthermore, EPA’s experience since 

2018 is that allowing for alternative Step 

2 thresholds may be impractical or 

otherwise inadvisable for a number of 

additional policy reasons. For a regional 

air pollutant such as ozone, consistency 

in requirements and expectations across 

all states is essential. Based on its 

review of submittals to-date and after 

further consideration of the policy 

implications of attempting to recognize 

an alternative Step 2 threshold for 

certain states, the Agency now believes 

the attempted use of different thresholds 

at Step 2 with respect to the 2015 8-hour 

ozone NAAQS raises substantial policy 

consistency and practical 

implementation concerns.30 The 

availability of different thresholds at 

Step 2 has the potential to result in 

inconsistent application of good 

neighbor obligations based solely on the 

strength of a state’s implementation 

plan submittal at Step 2 of the 4-step 

interstate transport framework. From the 

perspective of ensuring effective 

regional implementation of good 

neighbor obligations, the more 

important analysis is the evaluation of 

the emissions reductions needed, if any, 

to address a state’s significant 

contribution after consideration of a 

multifactor analysis at Step 3, including 

a detailed evaluation that considers air 

quality factors and cost. Where 

alternative thresholds for purposes of 

Step 2 may be ‘‘similar’’ in terms of 

capturing the relative amount of upwind 

contribution (as described in the August 

2018 memorandum), nonetheless, use of 

an alternative threshold would allow 

certain states to avoid further evaluation 

of potential emission controls while 

other states must proceed to a Step 3 

analysis. This can create significant 

equity and consistency problems among 

states. 

Further, it is not clear that national 

ozone transport policy is best served by 

allowing for less stringent thresholds at 

Step 2. EPA recognized in the August 

2018 memorandum that there was some 

similarity in the amount of total upwind 

contribution captured (on a nationwide 

basis) between 1 percent and 1 ppb. 

However, EPA notes that while this may 

be true in some sense, that is hardly a 

compelling basis to move to a 1 ppb 

threshold. Indeed, the 1 ppb threshold 

has the disadvantage of losing a certain 

amount of total upwind contribution for 

further evaluation at Step 3 (e.g., 

roughly 7 percent of total upwind state 

contribution was lost according to the 

modeling underlying the August 2018 

memorandum; 31 in EPA’s updated 

modeling, the amount lost is 5 percent). 

Considering the core statutory objective 

of ensuring elimination of all significant 

contribution to nonattainment or 

interference of the NAAQS in other 

states and the broad, regional nature of 

the collective contribution problem with 

respect to ozone, there does not appear 

to be a compelling policy imperative in 

allowing some states to use a 1 ppb 

threshold while others rely on a 1 

percent of the NAAQS threshold. 

Consistency with past interstate 

transport actions such as CSAPR, and 

the CSAPR Update and Revised CSAPR 

Update rulemakings (which used a Step 

2 threshold of 1 percent of the NAAQS 

for two less stringent ozone NAAQS), is 

also important. Continuing to use a 1 

percent of NAAQS approach ensures 

that as the NAAQS are revised and 

made more stringent, an appropriate 

increase in stringency at Step 2 occurs, 

so as to ensure an appropriately larger 

amount of total upwind-state 

contribution is captured for purposes of 

fully addressing interstate transport. See 

76 FR 48208, 48237–38 (August 8, 

2011). 

Therefore, notwithstanding the 

August 2018 memorandum’s 

recognition of the potential viability of 

alternative Step 2 thresholds, and in 

particular, a potentially applicable 1 

ppb threshold, EPA’s experience since 

the issuance of that memorandum has 

revealed substantial programmatic and 

policy difficulties in attempting to 

implement this approach. Nonetheless, 

EPA is not at this time rescinding the 

August 2018 memorandum. As 

discussed further below, the basis for 

disapproval of Alabama, Mississippi, 

and Tennessee’s SIP submissions with 

respect to the Step 2 analysis is, in the 

Agency’s view, warranted even under 

the terms of the August 2018 

memorandum. EPA invites comment on 

this broader discussion of issues 

associated with alternative thresholds at 

Step 2. Depending on comment and 

further evaluation of this issue, EPA 

may determine to rescind the August 

2018 memorandum in the future. 

4. Step 3 of the 4-Step Interstate 

Transport Framework 

Consistent with EPA’s longstanding 

approach to eliminating significant 

contribution or interference with 

maintenance, at Step 3, states linked at 

Steps 1 and 2 are generally expected to 

prepare a multifactor assessment of 

potential emissions controls. EPA’s 

analysis at Step 3 in prior Federal 

actions addressing interstate transport 

requirements has primarily focused on 

an evaluation of cost-effectiveness of 

potential emissions controls (on a 

marginal cost-per-ton basis), the total 

emissions reductions that may be 

achieved by requiring such controls (if 

applied across all linked upwind states), 

and an evaluation of the air quality 

impacts such emissions reductions 

would have on the downwind receptors 

to which a state is linked; other factors 

may potentially be relevant if 

adequately supported. In general, where 

EPA’s or alternative air quality and 

contribution modeling establishes that a 

state is linked at Steps 1 and 2, it will 

be insufficient at Step 3 for a state 

merely to point to its existing rules 

requiring control measures as a basis for 

approval. In general, the emissionsreducing effects of all existing emissions 

control requirements are already 

reflected in the air quality results of the 

modeling for Steps 1 and 2. If the state 

is shown to still be linked to one or 

more downwind receptor(s), states must 

provide a well-documented evaluation 

determining whether their emissions 

constitute significant contribution or 

interference with maintenance by 

evaluating additional available control 

opportunities by preparing a multifactor 

assessment. While EPA has not 

prescribed a particular method for this 

assessment, EPA expects states at a 

minimum to present a sufficient 

technical evaluation. This would 

typically include information on 

emissions sources, applicable control 

technologies, emissions reductions, 

costs, cost effectiveness, and downwind 

air quality impacts of the estimated 

reductions, before concluding that no 


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32As examples of general approaches for how 

such an analysis could be conducted for their 

sources, states could look to the CSAPR Update, 81 

FR 74504, 74539–51; CSAPR, 76 FR 48208, 48246– 

63; CAIR, 70 FR 25162, 25195–229; or the NOX SIP 

Call, 63 FR 57356, 57399–405. See also Revised 

CSAPR Update, 86 FR 23054, 23086–23116. 

Consistently across these rulemakings, EPA has 

developed emissions inventories, analyzed different 

levels of control stringency at different cost 

thresholds, and assessed resulting downwind air 

quality improvements. 

33The August 20, 2018, SIP submission provided 

by ADEM was received by EPA on August 27, 2018. 

34On August 20, 2018, Alabama submitted 

multiple SIP revisions under one cover letter. EPA 

is only acting on Alabama’s 2015 ozone good 

neighbor interstate transport SIP requirements in 

this notice. 

35EPA notes that Alabama’s SIP submission is not 

organized around EPA’s 4-step framework for 

assessing good neighbor obligations, but EPA 

summarizes the submission using that framework 

for clarity here. 

36Alabama’s submission cites the following SIP 

approved regulations: Administrative Code Rule 

335–3–6, ‘‘Control of Organic Emissions’’, 335–3–8, 

‘‘Control of Nitrogen Oxides Emissions’’, 335–3–14– 

.01, ‘‘General Provisions’’, 335–3–14–.02, ‘‘Permit 

Procedures’’, 335–3–14–.03, ‘‘Standards for 

Granting Permits’’, 335–3–14– .04, ‘‘Air Permits 

Authorizing Construction in in Clean Air Areas 

[Prevention of Significant Deterioration Permitting 

(PSD)]’’ and 335–3–14–.05, ‘‘Air Permits 

Authorizing Construction in or Near Nonattainment 

Areas.’’ Alabama’s Submission cites the following 

Federal Rules: EPA’s Tier 1 and 2 mobile source 

rules, EPA’s nonroad Diesel Rule, EPA’s 2007 

Heavy-duty Highway Rule, New Source 

Performance Standards, National Emission 

Standards for Hazardous Air Pollutants, and 

CSAPR. 

37Alabama’s SIP references CSAPR, which covers 

the NOX ozone season trading program established 

in EPA’s 2011 CSAPR, 76 FR 48208 (August 8, 

2011). In addition, Alabama’s submittal includes a 

reference to the SIP-approved rules that adopted the 

CSAPR Update, 81 FR 74504 (October 26, 2016). 

See 82 FR 46674 (October 6, 2017). 

38See 81 FR 59869 (August 31, 2016), 82 FR 

46674 (October 6, 2017) (adopting Alabama 

Administrative Code Rule 335–3–8, ’’Control of 

Nitrogen Oxides Emissions’’ and adopting revisions 

to Rule 335–3–8 into the SIP). 

additional emissions controls should be 

required.32

5. Step 4 of the 4-Step Interstate 

Transport Framework 

At Step 4, states (or EPA) develop 

permanent and federally enforceable 

control strategies to achieve the 

emissions reductions determined to be 

necessary at Step 3 to eliminate 

significant contribution to 

nonattainment or interference with 

maintenance of the NAAQS. For a state 

linked at Steps 1 and 2 to rely on an 

emissions control measure at Step 3 to 

address its interstate transport 

obligations, that measure must be 

included in the state’s implementation 

plan so that it is permanent and 

federally enforceable. See CAA section 

110(a)(2)(D) (‘‘Each such [SIP] shall . . . 

contain adequate provisions . . . .’’). 

See also CAA section 110(a)(2)(A); 

Committee for a Better Arvin v. EPA, 

786 F.3d 1169, 1175–76 (9th Cir. 2015) 

(holding that measures relied on by a 

state to meet CAA requirements must be 

included in the SIP). 

II. SIP Submissions and EPA’s 

Evaluation 

A. Alabama 

The following section provides 

information related to Alabama’s SIP 

submission addressing interstate 

transport requirements for the 2015 8- 

hour ozone NAAQS, and EPA’s analysis 

of Alabama’s submission. 

1. Summary of Alabama’s 2015 Ozone 

Interstate Transport SIP Submission 

On August 20, 2018,33 Alabama 

submitted a SIP revision addressing the 

CAA section 110(a)(2)(D)(i)(I) good 

neighbor interstate transport 

requirements for the 2015 8-hour ozone 

NAAQS.34 The SIP submission 

provided Alabama’s analysis of its 

impact to downwind states and 

concluded that emissions from the State 

will not significantly contribute to 

nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in other states, based on 

modeling results included in EPA’s 

March 2018 memorandum. Alabama’s 

submission relied on the results of 

EPA’s modeling of 2023 using a 2011 

base year, as contained in the March 

2018 memorandum (which the State 

attached to its submittal), to identify 

downwind nonattainment and 

maintenance receptors that may be 

impacted by emissions from sources in 

the State at Step 1 of the 4-step 

framework.35

Alabama Department of 

Environmental Management (ADEM) 

reviewed this modeling, concurred with 

the results, and determined that the 

future year projections were appropriate 

for the purposes of evaluating 

Alabama’s impact on nonattainment and 

maintenance receptors in other states at 

Step 1. Alabama used this information 

to find that emissions from Alabama 

would not contribute above 1 percent of 

the NAAQS at any projected 

nonattainment or maintenance receptors 

at Step 2 of the 4-step framework (using 

EPA’s approach to defining such 

receptors). 

Alabama’s August 20, 2018, submittal 

also identified existing SIP-approved 

regulations and Federal programs 36 that 

ADEM noted regulate ozone-precursor 

emissions from sources in the State, 

including CSAPR trading programs.37

Alabama’s submission acknowledges 

that CSAPR does not address interstate 

transport for the 2015 ozone standard 

but does provide residual NOX

emissions reductions and notes the 

adoption of CSAPR NOX ozone season 

trading programs into the Alabama SIP 

on August 31, 2016, and October 6, 

2017.38 Alabama notes that the 

implementation of the existing SIPapproved regulations and Federal 

programs provide for a decline in ozone 

precursors emissions in the State. 

Alabama also stated that ozoneprecursor emissions would continue to 

decline in the State. 

Based on the information from 

Alabama’s transport SIP, ADEM 

concluded that emissions from Alabama 

sources will not significantly contribute 

to nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state. 

2. Prior Notices Related to Alabama’s 

SIP Submission 

Previously, EPA proposed approval of 

Alabama’s interstate transport 

provisions for the 2015 8-hour ozone 

NAAQS as addressed in Alabama’s 

August 20, 2018 SIP submission and 

based on the contribution modeling 

provided in the March 2018 

memorandum. See 84 FR 71854 

(December 30, 2019). When EPA 

completed updated modeling of 2023 in 

2020 using a 2016-based emissions 

modeling platform (2016v1), it became 

evident that Alabama was projected to 

be linked to downwind nonattainment 

and maintenance receptors (see footnote 

40 below). As a result, EPA deferred 

acting on Alabama’s SIP submittal when 

it published a supplemental proposal in 

2021 to approve four other southeastern 

states’ good neighbor SIP submissions 

using the updated 2023 modeling. See 

86 FR 37942, 37943 (July 19, 2021). The 

updated 2023 modeling using an 

updated 2016-based emissions modeling 

platform (2016v2) confirms the prior 

2016-based modeling of 2023 in that it 

continues to show Alabama is linked to 

at least one downwind nonattainment or 

maintenance receptor. Based on this 

updated modeling using the 2016-based 

emissions modeling platform, discussed 

in section I.C above, EPA is now 

withdrawing its 2019 proposed approval 

on Alabama’s September 13, 2018, 

interstate transport SIP as published on 

December 30, 2019, at 84 FR 71854. 

3. EPA’s Evaluation of Alabama’s 2015 

Ozone Interstate Transport SIP 

Submission 

EPA is proposing to find that 

Alabama’s August 20, 2018, SIP 

submission does not meet Alabama’s 

obligations with respect to prohibiting 

emissions that contribute significantly 


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39The ozone design values and contributions at 

individual monitoring sites nationwide are 

provided in the file ‘‘2016v2_DVs_state_

contributions.xlsx’’ which is included in Docket 

No. EPA–HQ–OAR–2021–0663. 

40These modeling results are consistent with the 

results of a prior round of 2023 modeling using the 

2016v1 emissions platform which became available 

to the public in the fall of 2020 in the Revised 

CSAPR Update, as noted in section I. That modeling 

showed that Alabama had a maximum contribution 

greater than 0.70 ppb to at least one nonattainment 

or maintenance-only receptor in 2023. These 

modeling results are included in the file ‘‘Ozone 

Design Values And Contributions Revised CSAPR 

Update.xlsx’’ in Docket No. EPA–HQ–OAR–2021– 

0663. 

41To the extent that Alabama’s submittal 

included information regarding emissions controls 

that could be interpreted as relevant to a step 3 

analysis, EPA evaluates that information in section 

II.A.3.d. 

to nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state based on 

EPA’s evaluation of the SIP submission 

using the 4-step interstate transport 

framework, and EPA is therefore 

proposing to disapprove Alabama’s SIP 

submission. 

(a) Results of EPA’s Step 1 and Step 2 

Modeling and Findings for Alabama 

As described in section I, EPA 

performed updated air quality modeling 

to project design values and 

contributions for 2023. These data were 

examined to determine if Alabama 

contributes at or above the threshold of 

1 percent of the 2015 8-hour ozone 

NAAQS (0.70 ppb) to any downwind 

nonattainment or maintenance receptor. 

As shown in Table 1, the data 39 indicate 

that in 2023, emissions from Alabama 

contribute greater than 1 percent of the 

standard to a nonattainment receptor in 

Harris County, Texas (ID#: 482010055) 

and a maintenance-only receptor in 

Denton County, Texas (ID#: 

481210034).40

TABLE 1—ALABAMA LINKAGE RESULTS BASED ON EPA UPDATED 2023 MODELING

Receptor ID Location Nonattainment/maintenance 

2023 Average 

design value 

(ppb) 

2023 

Maximum 

design value 

(ppb) 

Alabama 

contribution 

(ppb) 

482010055 ............................. Harris County, Texas ............ Nonattainment ...................... 71.0 72.0 0.88 

481210034 ............................. Denton County, Texas .......... Maintenance ......................... 70.4 72.2 0.71 

(b) Evaluation of Information Provided 

by Alabama Regarding Step 1 

At Step 1 of the 4-step interstate 

transport framework, Alabama relied on 

EPA modeling included in the March 

2018 memorandum to identify 

nonattainment and maintenance 

receptors in 2023. As described in 

section II.A.3.a, EPA has recently 

updated this modeling using the most 

current and technically appropriate 

information. EPA proposes to rely on 

EPA’s most recent modeling to identify 

nonattainment and maintenance 

receptors in 2023. That information 

establishes that there are two receptors 

to which Alabama is projected to be 

linked in 2023. 

(c) Evaluation of Information Provided 

by Alabama Regarding Step 2 

At Step 2 of the 4-step interstate 

transport framework, Alabama relied on 

EPA modeling released in the March 

2018 memorandum to identify upwind 

state linkages to nonattainment and 

maintenance receptors in 2023. As 

described in section I.C of this notice, 

EPA has recently updated modeling to 

identify upwind state contributions to 

nonattainment and maintenance 

receptors in 2023. In this action, EPA 

proposes to rely on the Agency’s most 

recently available modeling to identify 

upwind contributions and ‘‘linkages’’ to 

downwind air quality problems in 2023 

using a threshold of 1 percent of the 

NAAQS. See section I.D for a general 

explanation of the use of 1 percent of 

the NAAQS. 

As shown in Table 1, updated EPA 

modeling identifies Alabama’s 

maximum contribution to downwind 

nonattainment and maintenance 

receptors as greater than 1 percent of the 

standard (i.e., 0.70 ppb). Therefore, the 

State is linked to a downwind air 

quality problem at Steps 1 and 2. 

Because the entire technical basis for 

Alabama’s interstate transport SIP 

submission is that Alabama is not 

linked at Step 2, and thus Alabama’s SIP 

contains the necessary provisions to 

eliminate emissions that will contribute 

significantly to nonattainment or 

interfere with maintenance of the 2015 

8-hour ozone NAAQS in any other state, 

EPA proposes to disapprove Alabama’s 

SIP submission based on EPA’s finding 

that such a linkage does exist.41

Although Alabama did not rely on the 

1 ppb threshold in its SIP submittal, 

EPA recognizes that the most recently 

available EPA modeling at the time 

Alabama submitted its SIP submittal 

indicated that Alabama did not 

contribute above 1 percent of the 

NAAQS to a projected downwind 

nonattainment or maintenance receptor. 

Therefore, Alabama may not have 

considered analyzing the reasonableness 

and appropriateness of a 1 ppb 

threshold at Step 2 of the 4-step 

interstate transport framework per the 

August 2018 memorandum. However, 

EPA’s August 2018 memorandum 

provided that whether use of a 1 ppb 

threshold is appropriate must be based 

on an evaluation of state-specific 

circumstances, and no such evaluation 

was included in the submittal. EPA’s 

experience with the alternative Step 2 

thresholds is further discussed in 

section I.D.3.a. As discussed there, EPA 

is considering withdrawing the August 

2018 memorandum. 

(d) Evaluation of Information Provided 

by Alabama Regarding Step 3 

At Step 3 of the 4-step interstate 

transport framework, a state’s emissions 

are further evaluated, in light of 

multiple factors, including air quality 

and cost considerations, to determine 

what, if any, emissions significantly 

contribute to nonattainment or interfere 

with maintenance and, thus, must be 

eliminated under CAA section 

110(a)(2)(D)(i)(I). 

To effectively evaluate which 

emissions in the state should be deemed 

‘‘significant’’ and therefore prohibited, 

states generally should prepare an 

accounting of sources and other 

emissions activity for relevant 

pollutants and assess potential, 

additional emissions reduction 

opportunities and resulting downwind 

air quality improvements. EPA has 

consistently applied this general 

approach (i.e., Step 3 of the 4-step 

interstate transport framework) when 

identifying emissions contributions that 

the Agency has determined to be 

‘‘significant’’ (or interfere with 

maintenance) in each of its prior 

Federal, regional ozone transport 

rulemakings, and this interpretation of 

the statute has been upheld by the 

Supreme Court. See EME Homer City, 


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42See 81 FR 59869 (August 31, 2016), 82 FR 

46674 (October 6, 2017) (adopting Alabama 

Administrative Code Rule 335–3–8, ’’Control of 

Nitrogen Oxides Emissions’’ and adopting revisions 

to Rule 335–3–8 into the SIP). 

43The September 3, 2019, SIP submission 

provided by MDEQ was received by EPA on 

September 6, 2019. 

572 U.S. 489, 519 (2014). While EPA has 

not directed states that they must 

conduct a Step 3 analysis in precisely 

the manner EPA has done in its prior 

regional transport rulemakings, state 

implementation plans addressing the 

obligations in CAA section 

110(a)(2)(D)(i)(I) must prohibit ‘‘any 

source or other type of emissions 

activity within the State’’ from emitting 

air pollutants which will contribute 

significantly to downwind air quality 

problems. Thus, states must complete 

something similar to EPA’s analysis (or 

an alternative approach to defining 

‘‘significance’’ that comports with the 

statute’s objectives) to determine 

whether and to what degree emissions 

from a state should be ‘‘prohibited’’ to 

eliminate emissions that will 

‘‘contribute significantly to 

nonattainment in or interfere with 

maintenance of’’ the NAAQS in any 

other state. Alabama did not conduct 

such an analysis in its SIP submission. 

Based on Alabama’s finding that 

emissions from Alabama do not 

contribute above 1 percent of the 

NAAQS at any monitors that are 

projected to be in nonattainment or 

maintenance, the SIP submission 

identified SIP-approved provisions and 

Federal programs in the context that no 

further emissions reductions were 

necessary, and determined that the SIP 

contained adequate provisions to 

prohibit emissions that will 

significantly contribute to 

nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state. However, the 

State did not analyze total ozone 

precursors that continue to be emitted 

from sources and other emissions 

activity within the State, evaluate the 

emissions reduction potential of any 

additional controls using cost or other 

metrics, nor evaluate any resulting 

downwind air quality improvements 

that could result from such controls. 

Among the Federal programs 

referenced in Alabama’s submission was 

the NOX ozone season trading program 

of CSAPR for the 2008 ozone standard, 

which ADEM adopted into the Alabama 

SIP.42 This reference suggests that 

Alabama may have intended to rely on 

its electric generating units (EGUs) 

being subject to CSAPR Update (which 

reflected a stringency at the nominal 

marginal cost threshold of $1,400/ton 

(in 2011 dollars) for the 2008 8-hour 

ozone NAAQS) to argue that it has 

already implemented all cost-effective 

emissions reductions at EGUs. 

EPA does not support the concept that 

reliance on CSAPR Update is 

appropriate to conclude that no further 

emissions reductions are necessary 

under Step 3 for the 2015 8-hour ozone 

NAAQS. First, CSAPR Update did not 

regulate non-electric generating units 

(non-EGUs), and thus this analysis, even 

for the 2008 ozone NAAQS, was 

incomplete, and EPA acknowledged at 

the time that CSAPR Update was not a 

full remedy for interstate transport 

under that NAAQS. See Wisconsin, 938 

F.3d at 318–20. Second, relying on 

CSAPR Update’s (or any other CAA 

program’s) determination of costeffectiveness without further Step 3 

analysis is not approvable. Costeffectiveness must be assessed in the 

context of the specific CAA program; 

assessing cost-effectiveness in the 

context of ozone transport should reflect 

a more comprehensive evaluation of the 

nature of the interstate transport 

problem, the total emissions reductions 

available at several cost thresholds, and 

the air quality impacts of the reductions 

at downwind receptors. While EPA has 

not established a benchmark costeffectiveness value for 2015 8-hour 

ozone NAAQS interstate transport 

obligations, it is reasonable to expect 

control measures or strategies to address 

interstate transport under this NAAQS 

to reflect higher marginal control costs 

because the 2015 8-hour ozone NAAQS 

is a more stringent and more protective 

air quality standard. As such, the 

marginal cost threshold of $1,400/ton 

for the CSAPR Update (which addresses 

the 2008 ozone 8-hour NAAQS and is in 

2011 dollars) is not an appropriate cost 

threshold and cannot be approved as a 

benchmark to use for interstate transport 

SIP submissions for the 2015 8-hour 

ozone NAAQS. In addition, the updated 

EPA modeling captures all existing 

CSAPR trading programs in the 

baseline, and that modeling confirms 

that these control programs were not 

sufficient to eliminate the Alabama’s 

linkage at Steps 1 and 2 under the 2015 

8-hour ozone NAAQS even if the 

CSAPR Update provisions had been 

adopted into Alabama’s SIP. The State 

was therefore obligated at Step 3 to 

assess additional control measures 

using a multifactor analysis. 

As mentioned above, EPA has newly 

available information that indicates 

sources in Alabama are linked to 

downwind air quality problems for the 

2015 ozone standard. Therefore, EPA 

proposes to disapprove Alabama’s 

August 20, 2018, interstate transport SIP 

submission on the separate, additional 

basis that the SIP submittal did not 

assess additional emissions control 

opportunities. 

(e) Evaluation of Information Provided 

by Alabama Regarding Step 4 

Step 4 of the 4-step interstate 

transport framework calls for 

development of permanent and 

federally enforceable control strategies 

to achieve the emissions reductions 

determined to be necessary at Step 3 to 

eliminate significant contribution to 

nonattainment or interference with 

maintenance of the NAAQS. As 

mentioned in section II.A.3.d, 

Alabama’s SIP submission did not 

contain an evaluation of additional 

emissions control opportunities (or 

establish that no additional controls are 

required), thus, no information was 

provided at Step 4. As a result, EPA 

proposes to disapprove Alabama’s 

August 20, 2018, submittal on the 

separate, additional basis that the State 

has not developed permanent and 

enforceable emissions reductions 

necessary to meet the obligations of 

CAA section 110(a)(2)(d)(i)(I). 

4. Conclusion for Alabama 

Based on EPA’s evaluation of 

Alabama’s SIP submission and after 

consideration of updated EPA modeling 

using the 2016-based emissions 

modeling platform, EPA is proposing to 

find that the 2015 8-hour ozone NAAQS 

good neighbor interstate transport 

portion of Alabama’s August 20, 2018, 

SIP submission addressing CAA section 

110(a)(2)(D)(i)(I) does not meet the 

State’s interstate transport obligations 

because it fails to contain the necessary 

provisions to eliminate emissions that 

will contribute significantly to 

nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state. 

B. Mississippi 

The following section provides 

information related to Mississippi’s SIP 

submission addressing interstate 

transport requirements for the 2015 8- 

hour ozone NAAQS, and EPA’s analysis 

of Mississippi’s submission. 

1. Summary of Mississippi’s 2015 

Ozone Interstate Transport SIP 

Submission 

On September 3, 2019, the 

Mississippi Department of 

Environmental Quality (MDEQ) 

submitted a SIP revision addressing the 

CAA section 110(a)(2)(D)(i)(I) interstate 

transport requirements for the 2015 8- 

hour ozone NAAQS.43 The SIP 


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44EPA notes that Mississippi’s September 2, 

2019, SIP submission is not organized around EPA’s 

4-step interstate transport framework for assessing 

good neighbor obligations, but EPA summarizes the 

submission using that framework for clarity here. 

45See section I.D, above for a discussion of EPA’s 

approach to identify maintenance receptors. 

submission provided Mississippi’s 

analysis of its impact to downwind 

states and concluded that emissions 

from the State will not significantly 

contribute to nonattainment or interfere 

with maintenance of the 2015 8-hour 

ozone NAAQS in other states. 

MDEQ’s submission relied on the 

results of EPA’s modeling for the 2015 

8-hour ozone NAAQS, contained in the 

March 2018 memorandum, to identify 

projected downwind nonattainment and 

maintenance receptors and contribution 

linkages in 2023 that may be impacted 

by emissions from sources in 

Mississippi at Steps 1 and 2 of the 4- 

step interstate transport framework,44

respectively. MDEQ reviewed EPA’s 

March 2018 modeling and found that 

the modeled contributions for 

Mississippi were below 1 percent of the 

NAAQS for all nonattainment and 

maintenance receptors, except the Deer 

Park nonattainment receptor in Harris 

County, Texas (Monitor ID: 482011039). 

The SIP submission identified 

Mississippi as linked to the Deer Park 

receptor with an upwind contribution of 

0.79 ppb. 

In its submittal, MDEQ discussed 

EPA’s August 2018 memorandum, 

explaining that 0.79 ppb is 1.12 percent 

of the 2015 8-hour ozone NAAQS, 

which is greater than the 1 percent 

contribution threshold of 0.70 ppb but 

less than a 1 ppb alternative 

contribution threshold. The SIP 

submission also states that the Deer Park 

receptor design value was projected to 

be greater than the 2015 ozone standard 

in 2023, but that the actual 2015–2017 

design value was below the NAAQS at 

68 ppb. Based on the modeling in the 

March 2018 memo, along with 

application of a 1 ppb alternative 

contribution threshold and information 

regarding 2015–2017 monitored values 

at the Deer Park receptor, MDEQ 

concluded that sources in Mississippi 

were not linked to downwind 

nonattainment or maintenance receptors 

at Step 2, and therefore, the State does 

not significantly contribute to 

nonattainment in another state for the 

2015 ozone standard. Further, MDEQ 

stated that the SIP contains adequate 

provisions to prohibit sources and other 

types of emissions activities within the 

State from contributing to 

nonattainment in another state with 

respect to the 2015 8-hour ozone 

NAAQS. 

In its submission, MDEQ treated the 

Deer Park receptor as a maintenance 

receptor because the most recent 

measured design value at the time of its 

submission (i.e., the 2017 design value 

of 68 ppb) was below the level of the 

NAAQS at this monitor. Based on 

MDEQ’s interpretation of EPA’s October 

19, 2018, memorandum, the State 

eliminated the Deer Park monitor site in 

Harris County, Texas, as a maintenance 

receptor in 2023 (although EPA’s 

modeling of 2023 released with the 

October 2017 memorandum had 

identified this monitoring site as a 

nonattainment receptor). 

To support eliminating the Deer Park 

monitor as a receptor, MDEQ’s 

demonstration included: (1) Evaluating 

ozone season temperatures in the period 

2014–2017 in Harris County to 

determine if conditions were conducive 

for ozone formation; (2) assessing 

monitored ozone design values from 

2011–2017 at the Deer Park monitor; 

and (3) reviewing ozone precursor 

emission trends in the Houston Area, 

Texas (statewide), and Mississippi 

(statewide). In its demonstration, MDEQ 

stated that temperatures in 2015 and 

2016 were above average, and in 2014 

and 2017 temperatures were near 

normal. Based on this information, 

MDEQ concluded that conditions were 

conducive to ozone formation during 

this three-year time period (i.e., 2015 to 

2017). MDEQ’s submission also states 

that design values from 2011 to 2017 at 

the Deer Park receptor showed a 

downward trend and that design values 

have been meeting the 2015 8-hour 

ozone NAAQS since 2015. Further, 

according to the submittal, ozone 

precursor emissions in Texas and 

Mississippi both showed a downward 

trend based on data from 2008, 2011, 

and 2014. Based on the downward trend 

in emissions and the fact that the Deer 

Park monitor was measuring attainment 

in 2015, 2016, and 2017, MDEQ 

determined that the Deer Park receptor 

should be eliminated as a maintenance 

receptor. Thus, based on the elimination 

of the Deer Park receptor, along with 

application of a 1 ppb threshold, 

Mississippi concluded that the State did 

not significantly interfere with 

maintenance (prong 2) in another state 

for the 2015 ozone standard. 

In summary, MDEQ concluded that 

sources in the State do not significantly 

contribute to nonattainment or interfere 

with maintenance in another state, that 

no further emission reductions were 

necessary, and that Mississippi’s SIP 

contains adequate provisions to prevent 

sources and other types of emissions 

activities within the State from 

contributing significantly to 

nonattainment or interfering with 

maintenance in another state with 

respect to the 2015 8-hour ozone 

NAAQS. 

2. EPA’s Evaluation of Mississippi’s 

2015 Ozone Interstate Transport SIP 

Submission 

EPA is proposing to find that 

Mississippi’s September 3, 2019, SIP 

submission does not meet Mississippi’s 

obligations with respect to prohibiting 

emissions that contribute significantly 

to nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state based on 

EPA’s evaluation of the SIP submission 

using the 4-step interstate transport 

framework, and EPA is therefore 

proposing to disapprove Mississippi’s 

submission. 

(a) Evaluation of Information Provided 

by Mississippi Regarding Step 1 

At Step 1 of the 4-step interstate 

transport framework, MDEQ relied on 

EPA modeling released in the March 

2018 memorandum to identify 

nonattainment and maintenance 

receptors in 2023. 

In its submittal, MDEQ attempted to 

utilize the October 2018 memorandum 

along with 2014 to 2017 ozone design 

values (the most recent data available at 

the time of submittal) to eliminate the 

Deer Park receptor in Harris County, 

Texas (Monitor ID: 482011039) as a 

maintenance receptor. Table 2 of the 

submittal correctly indicates that this 

monitoring site was a projected 

nonattainment receptor, not a 

maintenance-only receptor, in 2023 

based on the EPA’s modeling data 

included in the March 2018 

memorandum. However, in its 

submittal, the State relied on the 2014 

to 2017 design values at the Deer Park 

receptor (i.e., 69 ppb, 67 ppb, and 68 

ppb, respectively) as the basis for stating 

that this receptor met EPA’s definition 

of a maintenance receptor. Based on this 

information, the State applied an 

alternative definition of a maintenance 

receptor utilizing the potential concepts 

included in the October 2018 

memorandum. This memorandum 

included a description of the approach 

that EPA has historically used to 

identify maintenance-only receptors 45

and identified potential alternate ways 

to define maintenance receptors based 

on certain criteria suggested in the 

memorandum including an evaluation 

of meteorology conductive to ozone 

formation, review of ozone monitored 

concentrations, and precursor emissions 

trends. 


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46See Attachment A of EPA’s October 2018 

memorandum formation to assess whether 

particular summers had ozone-conducive or 

unconducive meteorology within the 10-year period 

2008 through 2017. The memorandum states that 

meteorological conditions including temperature, 

humidity, winds, solar radiation, and vertical 

mixing affect the formation and transport of 

ambient ozone concentrations. The memorandum 

suggests generally that above average temperatures 

are an indication that meteorology is conducive to 

ozone formation and below average temperatures 

indicate that conditions are unconducive to ozone 

formation. Within a particular summer season, the 

degree that meteorology is conducive for ozone 

formation can vary from region to region and 

fluctuate with time within a particular region. 

47The data are given in ‘‘2010_thru_2020 Ozone 

Design Values.xlsx,’’ which is included in Docket 

No. EPA–HQ–OAR–2021–0663. 

48This is based on preliminary 2021 data 

available from the Air Quality System (AQS) as of 

January 3, 2022. The design values for 2021 have 

not been certified by state agencies. 

EPA recognized in the October 2018 

memorandum that states could 

potentially, with sufficient justification, 

establish an approach to addressing 

maintenance receptors that gives 

independent significance to prong 2 in 

some manner different than EPA’s 

approach. In addition, the October 2018 

memorandum identified two potential 

concepts that states could use to 

identify maintenance receptors: (1) 

States may, in some cases, eliminate a 

site as a maintenance receptor if the site 

is currently measuring clean data, or (2) 

in some cases, use a design value from 

the base period that is not the maximum 

design value. For either of these 

alternative methods, to adequately 

consider areas struggling to meet the 

NAAQS, EPA also indicated that it 

expects states to include with their SIP 

demonstration technical analyses 

showing that the following three criteria 

are met: 

• Meteorological conditions in the 

area of the monitoring site were 

conducive to ozone formation during 

the period of clean data or during the 

alternative base period design value 

used for projections; 46

• Ozone concentrations have been 

trending downward at the site since 

2011 (and ozone precursor emissions of 

NOX and VOC have also decreased); and 

• Emissions are expected to continue 

to decline in the upwind and downwind 

states out to the attainment date of the 

receptor. 

EPA’s October 2018 memorandum 

explained that the intent of these 

analyses is to demonstrate that 

monitoring sites that would be 

identified as maintenance receptors 

under EPA’s historical approach could 

nonetheless be shown to be very 

unlikely to violate the NAAQS in the 

future analytic year. 

However, the analysis provided by 

Mississippi in its submission has not 

met the criteria laid out in the guidance. 

With respect to the first criterion 

(meteorological conditions), MDEQ 

assessed ozone design values at the Deer 

Park site in Houston from 2014 to 2017 

and anomalies (i.e., difference compared 

to the long-term mean) of average 

temperatures in June, July, and August, 

summarized from EPA’s October 2018 

memorandum, to determine whether 

particular summers had ozoneconducive or unconducive meteorology 

during the period of clean data. MDEQ 

stated that temperatures were above 

average in 2015 and 2016 when the Deer 

Park monitor measured ozone 

concentrations below the 2015 8-hour 

ozone NAAQS and near normal in 2014 

and 2017. However, MDEQ’s review of 

meteorological conditions in the 

vicinity of the Deer Park monitor was 

limited to temperature anomalies and 

did not discuss or consider how other 

meteorological factors identified in the 

October 2018 memorandum (such as 

humidity, solar radiation, vertical 

mixing, and/or other meteorological 

indicators such as cooling-degree days) 

confirm whether conditions affecting 

the monitor may have been conducive 

to ozone formation in 2015 and 2016 

and unconducive in 2014 and 2017. 

With respect to the second criterion, 

MDEQ’s submission included 

information related to ozone design 

values and ozone precursors. 

Specifically, the submission included 

an assessment of ozone design values at 

the Deer Park monitor from 2011 to 

2017, which showed a downward trend 

in ozone concentrations. However, 

MDEQ’s SIP submission did not include 

a discussion of the 2018 design value, 

which showed a violation of the 2015 

standard at 71 ppb, even though that 

data was available and could have been 

considered in the State’s analysis at the 

time of the submission in 2019.47 In 

addition, the 2019 and 2020 design 

values, 75 ppb and 78 ppb, respectively, 

also exceeded the NAAQS. The 

preliminary design value for 2021 is 74 

ppb.48 Although not available at the 

time of the SIP submission, these more 

recent data suggest a continuous trend 

in measured ozone concentrations above 

the 2015 ozone standard at the Deer 

Park monitor. Even though MDEQ’s 

review of ozone monitoring data may 

have shown a decrease in measured 

concentration from 2011 to 2017, EPA 

notes a significant increase between the 

2017 and 2018 4th highest daily 

maximum concentration, from 68 ppb to 

85 ppb. MDEQ’s SIP submission did not 

consider the 2018 4th high daily 

maximum concentration as part of its 

trends analysis even though the 

information was available at the time 

the SIP was submitted to EPA. Thus, at 

the time of the submission, the Deer 

Park monitor had a 3-year design value 

of 71 ppb, which violated the 70 ppb 

ozone standard. Thus, under the terms 

of the October 2018 memorandum, 

Mississippi’s SIP submission does not 

adequately establish a basis for 

eliminating the Deer Park monitoring 

site as an ozone transport receptor. 

MDEQ also assessed total ozone 

precursor emissions data in 2008, 2011, 

and 2014, which MDEQ claimed 

indicated a decrease in ozone precursor 

(NOX and VOC) emissions in the 

Houston metropolitan statistical area, 

Texas (statewide), and Mississippi 

(statewide). While EPA acknowledges 

the general downward trends in NOX

and VOC emissions, the Deer Park 

monitor ozone concentrations design 

values through 2020 show recent 

measured ozone concentrations that 

exceed the 2015 ozone standard. 

Further, even accounting for emissions 

trends, EPA’s latest air quality 

modeling, as presented below, shows 

that there are now three receptors to 

which Mississippi contributes in 2023, 

not just one. Thus, the apparent 

downward trend in ozone precursors in 

Texas and Mississippi alone cannot 

support elimination of either the Deer 

Park monitor as a receptor (under the 

information Mississippi relied on) or the 

three Texas receptors to which EPA now 

finds Mississippi to be contributing. See 

section II.B.2.c and Table 2 below for 

results of EPA’s 2016v2 Step 1 and Step 

2 modeling and findings for Mississippi. 

With respect to the third criterion, 

MDEQ stated that, ‘‘[b]ased on national 

and regional emissions trends, and 

current regulations on point sources and 

mobile sources, emissions are expected 

to continue to decline in the upwind 

and downwind states.’’ However, the 

State did not cite any specific 

regulations controlling sources of ozone 

precursors or mobile sources or quantify 

the NOX emission reduction potential of 

current regulations for point and mobile 

sources. 

Based on the reasons stated above, 

EPA does not believe Mississippi’s SIP 

submission provided sufficient 

justification to eliminate the Deer Park 

monitor as a maintenance receptor. 

(b) Evaluation of Information Provided 

by Mississippi Regarding Step 2 

At Step 2 of the 4-step interstate 

transport framework, Mississippi relied 

on EPA’s modeling released in the 

March 2018 memorandum to identify 

upwind state linkages to nonattainment 

and maintenance receptors in 2023. 


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49Pursuant to section 107(d) of the CAA, EPA 

must designate areas as either ‘‘nonattainment,’’ 

‘‘attainment,’’ or ‘‘unclassifiable.’’ Historically for 

ozone, the EPA has designated most areas that do 

not meet the definition of nonattainment as 

‘‘unclassifiable/attainment.’’ This category includes 

areas that have air quality monitoring data meeting 

the NAAQS and areas that do not have monitors but 

for which the EPA has no evidence that the areas 

may be violating the NAAQS or contributing to a 

nearby violation. In the designations for the 2015 

ozone NAAQS, the EPA reversed the order of the 

label to be ‘‘attainment/unclassifiable’’ to better 

convey the definition of the designation category 

and so that the category is more easily 

distinguished from the separate unclassifiable 

category. An ‘‘attainment’’ designation is reserved 

for a previous nonattainment area that has been 

redesignated to attainment as a result of the EPA’s 

approval of a CAA section 175A maintenance plan 

submitted by the state air agency. 

50The ozone design values and contributions at 

individual monitoring sites nationwide are 

provided in the file ‘‘2016v2_DVs_state_

contributions.xlsx’’ which is included in Docket 

No. EPA–HQ–OAR–2021–0663. 

51These modeling results are consistent with the 

results of a prior round of 2023 modeling using a 

the 2016v1 emissions platform that became 

available to the public in the fall of 2020 in the 

Revised CSAPR Update, as noted in section I. 

As described in section I.C of this 

notice, EPA has recently updated 

modeling to identify upwind state 

contributions to nonattainment and 

maintenance receptors in 2023. In this 

proposal, EPA relies on the Agency’s 

most recently available modeling to 

identify upwind contributions and 

‘‘linkages’’ to downwind air quality 

problems in 2023 using a threshold of 

1 percent of the NAAQS. See section I.D 

for general explanation of the use of 1 

percent of the NAAQS. As shown in 

Table 2, updated EPA modeling 

identifies Mississippi’s maximum 

contribution to downwind 

nonattainment and maintenance 

receptors to be greater than 1 percent of 

the standard (i.e., 0.70 ppb). Therefore, 

the State is linked to a downwind air 

quality problem at Steps 1 and 2. 

MDEQ relied on EPA’s August 2018 

memorandum in an attempt justify 

using a 1 ppb alternative contribution 

threshold at Step 2 as a basis to assert 

that Mississippi would not be ‘‘linked’’ 

to any projected downwind 

nonattainment or maintenance 

receptors. As discussed in EPA’s August 

2018 memorandum, EPA had suggested 

that, with appropriate additional 

analysis, it may be reasonable for states 

to use a 1 ppb contribution threshold, as 

an alternative to a 1 percent threshold, 

at Step 2 of the 4-step interstate 

transport framework, for the purposes of 

identifying linkages to downwind 

receptors. However, based on EPA’s 

updated modeling, the State is projected 

to contribute greater than both the 1 

percent and alternative 1 ppb 

thresholds. While EPA does not, in this 

action, approve of the State’s 

application of the 1 ppb threshold, 

based on its linkages greater than 1 ppb 

to projected downwind nonattainment 

or maintenance receptors, the State’s 

use of this alternative threshold at Step 

2 of the 4-step interstate framework is 

inconsequential to EPA’s proposed 

action on this SIP. 

In addition, MDEQ’s SIP does not 

include a technical analysis to 

sufficiently justify use of an alternative 

1 ppb threshold at the Deer Park 

monitor. Echoing EPA’s August 2018 

memorandum, MDEQ stated that the 

amount of upwind collective 

contribution captured with the 1 

percent and 1 ppb thresholds is 

generally comparable. In this 

memorandum, EPA also determined 

that by capturing a percentage of 

upwind state emissions comparable to 

the amount captured at 1 percent, the 

alternative threshold may be 

appropriate, indicating that a more 

determinative conclusion of 

appropriateness would require further 

analysis. In this regard, MDEQ did not 

provide any further technical 

justification to make that determination. 

MDEQ also referred to an EPA 

Guidance on Significant Impact Levels 

for Ozone and Fine Particles in the 

Prevention of Significant Deterioration 

Permitting Program (‘‘SILs Guidance’’) 

as additional justification for use of a 1 

ppb threshold. However, MDEQ did not 

provide discussion or analysis 

containing information specific to 

Mississippi or the receptors to which its 

emissions are potentially linked, which 

is necessary to thoroughly evaluate the 

state-specific circumstances that could 

support approval. In addition, the State 

did not explain the relevance or 

applicability of a SILs Guidance to 

which it made reference. EPA’s SILs 

guidance relates to a different provision 

of the CAA regarding implementation of 

the prevention of significant 

deterioration (PSD) permitting program, 

i.e., a program that applies in areas that 

have been designated attainment 49 or 

unclassifiable for the NAAQS, and it is 

not applicable to the good neighbor 

provision, which requires states to 

eliminate significant contribution or 

interference with maintenance of the 

NAAQS at known and ongoing air 

quality problem areas in other states. 

The analytical gaps identified indicate 

that the submittal’s use of a 1 ppb 

threshold for the State is not 

approvable. EPA’s experience with the 

alternative Step 2 thresholds is further 

discussed in section I.D.3.a. As 

discussed there, EPA is considering 

withdrawing the August 2018 

memorandum. 

Despite the linkage EPA determines 

exists at Step 2, the State argued in its 

submittal that it should not be 

considered to significantly contribute to 

nonattainment or interfere with 

maintenance of the NAAQS in other 

states. EPA finds that conclusion is not 

approvable at Steps 1 or 2. Therefore, 

based on EPA’s evaluation of the 

information submitted by Mississippi, 

and based on EPA’s most recent 

modeling results for 2023, EPA proposes 

to find that Mississippi is linked at 

Steps 1 and 2 and has an obligation to 

assess potential emissions reductions 

from sources or other emissions activity 

at Step 3 of the 4-step framework. 

(c) Results of EPA’s 2016v2 Step 1 and 

Step 2 Modeling and Findings for 

Mississippi 

As described in section I, EPA 

performed air quality modeling using 

the 2016v2 emissions platform to 

project design values and contributions 

for 2023. These data were examined to 

determine if Mississippi contributes at 

or above the threshold of 1 percent of 

the 2015 8-hour ozone NAAQS (0.70 

ppb) to any downwind nonattainment 

or maintenance receptor. As shown in 

Table 2, the data 50 indicate that in 2023, 

emissions from Mississippi contribute 

greater than 1 percent of the standard to 

nonattainment or maintenance-only 

receptors in Denton County, Texas 

(Monitor ID: 481210034), Harris County, 

Texas (Monitor ID: 482010055), and 

Brazoria County, Texas (Monitor ID: 

480391004).51 Note that each of these 

monitors is currently measuring 

nonattainment based on 2020 design 

values of 72 ppb, 76 ppb, and 73 ppb 

at the Denton County, Harris County, 

and Brazoria County receptors, 

respectively. 


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52The September 13, 2019, SIP submission 

provided by TDEC was received by EPA on 

September 17, 2018. 

53On September 18, 2018, Tennessee submitted 

multiple SIP revisions under one cover letter. EPA 

is only acting on Tennessee’s 2015 ozone good 

neighbor interstate transport SIP requirements in 

this notice. 

54EPA notes that Tennessee’s SIP submission is 

not organized around EPA’s 4-step framework for 

assessing good neighbor obligations, but EPA 

summarizes the submission using that framework 

for clarity here. 

TABLE 2—MISSISSIPPI LINKAGE RESULTS BASED ON EPA UPDATED 2023 MODELING

Receptor ID Location Nonattainment/ 

maintenance 

2023 average 

design value 

(ppb) 

2023 

maximum 

design value 

(ppb) 

Mississippi 

contribution 

(ppb) 

481210034 ........................... Denton County, Texas ......... Maintenance ........................... 70.4 72.2 1.14 

482010055 ........................... Harris County, Texas ........... Nonattainment ......................... 71.0 72.0 1.04 

480391004 ........................... Brazoria County, Texas ....... Maintenance ........................... 70.1 72.3 0.92 

(d) Evaluation of Information Provided 

by Mississippi Regarding Step 3 

At Step 3 of the 4-step interstate 

transport framework, a state’s emissions 

are further evaluated, in light of 

multiple factors, including air quality 

and cost considerations, to determine 

what, if any, emissions significantly 

contribute to nonattainment or interfere 

with maintenance and, thus, must be 

eliminated under CAA section 

110(a)(2)(D)(i)(I). 

To effectively evaluate which 

emissions in the state should be deemed 

‘‘significant,’’ and therefore prohibited, 

states generally should prepare an 

accounting of sources and other 

emissions activity for relevant 

pollutants and assess potential, 

additional emissions reduction 

opportunities and resulting downwind 

air quality improvements. EPA has 

consistently applied this general 

approach (i.e., Step 3 of the 4-step 

interstate transport framework) when 

identifying emissions contributions that 

the Agency has determined to be 

‘‘significant’’ (or interfere with 

maintenance) in each of its prior 

Federal, regional ozone transport 

rulemakings, and this interpretation of 

the statute has been upheld by the 

Supreme Court. See EME Homer City, 

572 U.S. 489, 519 (2014). While EPA has 

not directed states that they must 

conduct a Step 3 analysis in precisely 

the manner EPA has done in its prior 

regional transport rulemakings, state 

implementation plans addressing the 

obligations in CAA section 

110(a)(2)(D)(i)(I) must prohibit ‘‘any 

source or other type of emissions 

activity within the State’’ from emitting 

air pollutants which will contribute 

significantly to downwind air quality 

problems. Thus, states must complete 

something similar to the EPA’s analysis 

(or an alternative approach to defining 

‘‘significance’’ that comports with the 

statute’s objectives) to determine 

whether and to what degree emissions 

from a state should be ‘‘prohibited’’ to 

eliminate emissions that will 

‘‘contribute significantly to 

nonattainment in or interfere with 

maintenance of’’ the NAAQS in any 

other state. Mississippi did not conduct 

such an analysis in its SIP submission. 

Mississippi did not include an 

accounting of sources or other emissions 

activity in the State along with an 

analysis of potential NOX emissions 

control technologies, their associated 

costs, estimated emissions reductions, 

and downwind air quality 

improvements. 

EPA’s evaluation of Mississippi’s 

submittal, in conjunction with its 2016- 

based modeling of 2023, indicates that 

ozone-precursor emissions from 

Mississippi are linked to downwind air 

quality problems for the 2015 ozone 

standard at Steps 1 and 2. However, 

Mississippi’s SIP submittal does not 

include a Step 3 analysis. EPA proposes 

to find that Mississippi was required to 

analyze emissions from the sources and 

other emissions activity from within the 

State to determine whether its 

contributions were significant, and EPA 

proposes to disapprove its submission 

because Mississippi’s submittal failed to 

do so. 

(e) Evaluation of Information Provided 

by Mississippi Regarding Step 4 

Step 4 of the 4-step interstate 

transport framework calls for 

development of permanent and 

federally enforceable control strategies 

to achieve the emissions reductions 

determined to be necessary at Step 3 to 

eliminate significant contribution to 

nonattainment or interference with 

maintenance of the NAAQS. As 

mentioned previously, Mississippi’s SIP 

submittal did not contain an evaluation 

of additional emission control 

opportunities (or establish that no 

additional controls are required), thus, 

no information was provided at Step 4. 

As a result, EPA proposes to disapprove 

Mississippi’s submittal on the separate, 

additional basis that the State has not 

developed permanent and enforceable 

emissions reductions necessary to meet 

the obligations of CAA section 

110(a)(2)(d)(i)(I). 

3. Conclusion for Mississippi 

Based on EPA’s evaluation of 

Mississippi’s SIP submission, EPA is 

proposing to find that Mississippi’s 

September 3, 2019, SIP submission 

addressing CAA section 

110(a)(2)(D)(i)(I) does not meet the 

State’s interstate transport obligations 

because it fails to contain the necessary 

provisions to eliminate emissions that 

will contribute significantly to 

nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state. 

C. Tennessee 

The following section provides 

information related to Tennessee’s SIP 

submission addressing interstate 

transport requirements for the 2015 8- 

hour ozone NAAQS, and EPA’s analysis 

of Tennessee’s submission. 

1. Summary of Tennessee’s 2015 Ozone 

Interstate Transport SIP Submission 

On September 13, 2018, Tennessee 

submitted a SIP revision addressing the 

CAA section 110(a)(2)(D)(i)(I) interstate 

transport requirements for the 2015 8- 

hour ozone NAAQS.52 53 The SIP 

submission provided Tennessee’s 

analysis of its impact to downwind 

states and concluded that emissions 

from the State will not significantly 

contribute to nonattainment or interfere 

with maintenance of the 2015 8-hour 

ozone NAAQS in other states. 

Tennessee’s submission relied on EPA’s 

modeling results for the 2015 8-hour 

ozone NAAQS, contained in the March 

2018 memorandum, to identify 

downwind nonattainment and 

maintenance receptors that may be 

impacted by emissions from sources in 

the State at Steps 1 and 2 of the 4-step 

framework.54 The Tennessee 

Department of Environmental Control 

(TDEC) reviewed EPA’s 2023 modeling, 

concurred with the results, and 

determined that EPA’s future year NOX

projections were reasonable and account 


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55The Tennessee SIP revision specifically cites 

the Federal NOX Budget Trading Program, CAIR, 

and CSAPR. In addition, the Tennessee SIP revision 

discusses Tennessee rule 1200–03–27–.12 (NOX SIP 

Call requirements for Stationary Boilers and 

Combustion Turbines), which had not been 

approved into the SIP at the time of the September 

13, 2018, submittal. EPA finalized approval of 

TAPR 1200–03–27–.12 into the Tennessee SIP on 

March 2, 2021. See 86 FR 12092. 

56See page 9 through 12 of Tennessee’s 

September 13, 2018, SIP submission for a list of 

SIP-approved State rules and Federal rules. This 

can be found in Docket No. EPA–R04–OAR–2021– 

0841. 

57The ozone design values and contributions at 

individual monitoring sites nationwide are 

provided in the file ‘‘2016v2_DVs_state_

contributions.xlsx’’ which is included in Docket 

No. EPA–HQ–OAR–2021–0663. 

58These modeling results are consistent with the 

results of a prior round of 2023 modeling using the 

2016v1 emissions platform which became available 

to the public in the fall of 2020 in the Revised 

CSAPR Update, as noted in section I. That modeling 

showed that Tennessee had a maximum 

contribution greater than 0.70 ppb to at least one 

nonattainment or maintenance-only receptor in 

2023. These modeling results are included in the 

file ‘‘Ozone Design Values And Contributions 

Revised CSAPR Update.xlsx’’ in Docket No. EPA– 

HQ–OAR–2021–0663. 

for source shutdowns, new controls, and 

fuel switches. TDEC summarized the 

State’s upwind contribution to 26 

nonattainment and maintenance 

receptors and noted Tennessee’s largest 

impact on any potential downwind 

receptor in 2023 would be 0.31 ppb and 

0.65 ppb, respectively. Tennessee found 

that—based on EPA’s 2023 modeling— 

emissions from Tennessee do not 

contribute above 1 percent of the 

NAAQS or above 1 ppb at any monitors 

that are projected to be in 

nonattainment or maintenance. 

Tennessee’s September 13, 2018, SIP 

submittal asserted that NOX emissions 

are considered the primary cause of 

formation of ozone in the southeast 

United States, and emphasized a 

significant reduction in NOX emissions 

reductions from coal-fired EGUs and 

other large NOX sources leading to 

improvements in air quality, including 

reductions attributable to previous 

transport rulemakings.55 Additionally, 

TDEC identifies existing SIP-approved 

provisions, Federal regulations and 

programs, court settlements, and 

statewide source shutdowns that TDEC 

believes limit ozone precursor 

emissions in the State.56

Based on the information contained in 

Tennessee’s transport SIP, TDEC 

concluded that Tennessee does not 

significantly contribute to 

nonattainment or interfere with 

maintenance in another state of the 2015 

8-hour ozone NAAQS, and that the SIP 

provides for adequate measures to 

control ozone precursor emissions. 

2. Prior Notices Related to Tennessee’s 

SIP Submission 

Previously, EPA proposed approval of 

Tennessee’s interstate transport 

provisions for the 2015 8-hour ozone 

NAAQS as addressed in Tennessee’s 

September 13, 2018, SIP submission and 

based on the contribution modeling 

provided in the March 2018 

memorandum. See 84 FR 71854 

(December 30, 2019). When EPA 

completed updated modeling of 2023 in 

2020 using a 2016-based emissions 

modeling platform (2016v1), it became 

evident that Tennessee was projected to 

be linked to downwind nonattainment 

and maintenance receptors (see footnote 

57 below). As a result, EPA deferred 

acting on Tennessee’s SIP submittal 

when it published a supplemental 

proposal in 2021 to approve four other 

southeastern states’ good neighbor SIP 

submissions, using the updated 2023 

modeling. See 86 FR 37942, 37943 (July 

19, 2021). The updated 2023 modeling 

presented in this proposal using an 

updated 2016-based emissions modeling 

platform (2016v2) confirms the prior 

2016-based modeling of 2023 in that it 

continues to show Tennessee is linked 

to at least one downwind nonattainment 

or maintenance receptor. Based on this 

updated modeling using the 2016-based 

emissions modeling platform, discussed 

in section I.C above, EPA is now 

withdrawing its 2019 proposed approval 

on Tennessee’s September 13, 2018, 

interstate transport SIP as published on 

December 30, 2019 at 84 FR 71854. 

3. EPA’s Evaluation of Tennessee’s 2015 

Ozone Interstate Transport SIP 

Submission 

EPA is proposing to find that 

Tennessee’s September 13, 2018, SIP 

submission does not meet the State’s 

obligations with respect to prohibiting 

emissions that contribute significantly 

to nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state based on 

EPA’s evaluation of the SIP submission 

using the 4-step interstate transport 

framework, and EPA is therefore 

proposing to disapprove Tennessee’s 

SIP submission. 

(a) Results of EPA’s Step 1 and Step 2 

Modeling and Findings for Tennessee 

As described in section I, EPA 

performed updated air quality modeling 

to project design values and 

contributions for 2023. These data were 

examined to determine if Tennessee 

contributes at or above the threshold of 

1 percent of the 2015 8-hour ozone 

NAAQS (0.70 ppb) to any downwind 

nonattainment or maintenance receptor. 

As shown in Table 3, the data 57 indicate 

that in 2023, emissions from Tennessee 

contribute greater than 1 percent of the 

standard to the maintenance-only 

receptor in Denton County, Texas (ID#: 

481210034).58

TABLE 3—TENNESSEE LINKAGE RESULTS BASED ON EPA UPDATED 2023 MODELING

Receptor ID Location Nonattainment/maintenance 

2023 Average 

design value 

(ppb) 

2023 

Maximum 

design value 

(ppb) 

Tennessee 

contribution 

(ppb) 

481210034 ............................. Denton County, Texas .......... Maintenance ......................... 70.4 72.2 0.94 

(b) Evaluation of Information Provided 

by Tennessee Regarding Step 1 

At Step 1 of the 4-step interstate 

transport framework, Tennessee relied 

on EPA modeling included in the March 

2018 memorandum to identify 

nonattainment and maintenance 

receptors in 2023. As described 

previously in section II.C.3.a, EPA has 

recently updated this modeling using 

the most current and technically 

appropriate information. EPA proposes 

to rely on EPA’s most recent modeling 

to identify nonattainment and 

maintenance receptors in 2023. That 

information establishes that there is one 

receptor to which Tennessee is 

projected to be linked in 2023. 

(c) Evaluation of Information Provided 

by Tennessee Regarding Step 2 

At Step 2 of the 4-step interstate 

transport framework, Tennessee relied 

on EPA modeling released in the March 

2018 memorandum to identify upwind 

state linkages to nonattainment and 

maintenance receptors in 2023. As 

described in section I.C of this notice, 


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59To the extent the Tennessee submittal included 

information regarding emissions controls that could 

be interpreted as relevant to a Step 3 analysis, EPA 

evaluates that information in section II.C.3.d. 60See footnote 49. 

EPA has recently updated modeling to 

identify upwind state contributions to 

nonattainment and maintenance 

receptors in 2023. In this proposal, EPA 

relies on the Agency’s most recently 

available modeling to identify upwind 

contributions and ‘‘linkages’’ to 

downwind air quality problems in 2023 

using a threshold of 1 percent of the 

NAAQS. See section I.D for a general 

explanation of the use of 1 percent of 

the NAAQS. 

As shown in Table 3, updated EPA 

modeling identifies Tennessee’s 

maximum contribution to a downwind 

maintenance receptor as greater than 1 

percent of the standard (i.e., 0.70 ppb). 

Therefore, the State is linked to a 

downwind air quality problem at Steps 

1 and 2. Because the entire technical 

basis for Tennessee’s submittal is that 

the State is not linked at Step 2, EPA 

proposes to disapprove Tennessee’s SIP 

submission based on EPA’s finding that 

a linkage does exist.59

Tennessee references a 1 ppb 

threshold in its submittal, citing to 

EPA’s SILs Guidance as justification for 

the use of a 1 ppb threshold. However, 

Tennessee did not provide additional 

discussion or analysis containing 

information specific to Tennessee or the 

receptors to which its emissions are 

potentially linked, which is necessary to 

evaluate the state-specific circumstances 

that could support approval of an 

alternative threshold. Nevertheless, EPA 

recognizes that the most recently 

available EPA modeling at the time 

Tennessee submitted its SIP submittal 

indicated the State did not contribute 

above 1 percent of the NAAQS to a 

projected downwind nonattainment or 

maintenance receptor. Therefore, the 

State may not have considered 

conducting an in-depth analysis as to 

the reasonableness and appropriateness 

of a 1 ppb threshold at Step 2 of the 4- 

step interstate transport framework per 

the August 2018 memorandum. 

However, EPA’s August 2018 

memorandum provided that whether 

use of a 1 ppb threshold is appropriate 

must be based on an evaluation of statespecific circumstances. Tennessee 

provided no such analysis. Further, the 

State did not explain the relevance of 

the SILs Guidance to which it made 

reference. This guidance relates to a 

different provision of the CAA regarding 

implementation of the PSD permitting 

program, i.e., a program that applies in 

areas that have been designated 

attainment 60 or unclassifiable for the 

NAAQS, and it is not applicable to the 

good neighbor provision, which requires 

states to eliminate significant 

contribution or interference with 

maintenance of the NAAQS at known 

and ongoing air quality problem areas in 

other states. 

EPA’s experience with the alternative 

Step 2 thresholds is further discussed in 

section I.D.3.a above. As discussed 

there, EPA is considering withdrawing 

the August 2018 memorandum. 

(d) Evaluation of Information Provided 

by Tennessee Regarding Step 3 

At Step 3 of the 4-step interstate 

transport framework, a state’s emissions 

are further evaluated, in light of 

multiple factors, including air quality 

and cost considerations, to determine 

what, if any, emissions significantly 

contribute to nonattainment or interfere 

with maintenance and, thus, must be 

eliminated under CAA section 

110(a)(2)(D)(i)(I). 

To effectively evaluate which 

emissions in the state should be deemed 

‘‘significant’’ and therefore prohibited, 

states generally should prepare an 

accounting of sources and other 

emissions activity for relevant 

pollutants and assess potential, 

additional emissions reduction 

opportunities and resulting downwind 

air quality improvements. EPA has 

consistently applied this general 

approach (i.e., Step 3 of the 4-step 

interstate transport framework) when 

identifying emissions contributions that 

the Agency has determined to be 

‘‘significant’’ (or interfere with 

maintenance) in each of its prior 

Federal, regional ozone transport 

rulemakings, and this interpretation of 

the statute has been upheld by the 

Supreme Court. See EME Homer City, 

572 U.S. 489, 519 (2014). While the EPA 

has not directed states that they must 

conduct a Step 3 analysis in precisely 

the manner the EPA has done in its 

prior regional transport rulemakings, 

state implementation plans addressing 

the obligations in CAA section 

110(a)(2)(D)(i)(I) must prohibit ‘‘any 

source or other type of emissions 

activity within the State’’ from emitting 

air pollutants which will contribute 

significantly to downwind air quality 

problems. Thus, states must complete 

something similar to the EPA’s analysis 

(or an alternative approach to defining 

‘‘significance’’ that comports with the 

statute’s objectives) to determine 

whether and to what degree emissions 

from a state should be ‘‘prohibited’’ to 

eliminate emissions that will 

‘‘contribute significantly to 

nonattainment in or interfere with 

maintenance of’’ the NAAQS in any 

other state. Tennessee did not conduct 

such an analysis in its SIP submission. 

The State did not analyze total ozone 

precursors that continue to be emitted 

from sources and other emissions 

activity within the State, evaluate the 

emissions reduction potential of any 

additional controls using cost or other 

metrics, nor evaluate any resulting 

downwind air quality improvements 

that could result from such controls. 

Instead, Tennessee included in its 

submittal a list of existing emissions 

control programs and measures in the 

State. However, EPA’s modeling already 

takes account of such measures. Despite 

these existing emissions controls, the 

State is projected in the most recent 

modeling to be linked to at least one 

downwind nonattainment or 

maintenance receptor. The State was 

therefore obligated at Step 3 to assess 

additional control measures using a 

multifactor analysis. 

As mentioned above, EPA has newly 

available information that indicates 

sources in Tennessee are linked to 

downwind air quality problems for the 

2015 ozone standard. Therefore, EPA 

proposes to disapprove Tennessee’s 

September 18, 2018, SIP submission on 

the separate, additional basis that the 

SIP submittal did not assess additional 

emissions control opportunities. 

(e) Evaluation of Information Provided 

by Tennessee Regarding Step 4 

Step 4 of the 4-step interstate 

transport framework calls for 

development of permanent and 

federally enforceable control strategies 

to achieve the emissions reductions 

determined to be necessary at Step 3 to 

eliminate significant contribution to 

nonattainment or interference with 

maintenance of the NAAQS. As 

mentioned in section II.C.3.d, 

Tennessee’s SIP submission did not 

contain an evaluation of additional 

emissions control opportunities (or 

establish that no additional controls are 

required), thus, no information was 

provided at Step 4. As a result, EPA 

proposes to disapprove Tennessee’s 

September 18, 2018, submittal on the 

separate, additional basis that the State 

has not developed permanent and 

enforceable emissions reductions 

necessary to meet the obligations of 

CAA section 110(a)(2)(d)(i)(I). 

4. Conclusion for Tennessee 

Based on EPA’s evaluation of 

Tennessee’s SIP submission and after 

consideration of updated EPA modeling 

using the 2016-based emissions 


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61 In deciding whether to invoke the exception by 

making and publishing a finding that an action is 

based on a determination of nationwide scope or 

effect, the Administrator takes into account a 

number of policy considerations, including his 

judgment balancing the benefit of obtaining the D.C. 

Circuit’s authoritative centralized review versus 

allowing development of the issue in other contexts 

and the best use of agency resources. 

modeling platform, EPA is proposing to 

find that the portion of Tennessee’s 

September 13, 2018, SIP submission 

addressing CAA section 

110(a)(2)(D)(i)(I) does not meet the 

State’s interstate transport obligations 

because it fails to contain the necessary 

provisions to eliminate emissions that 

will contribute significantly to 

nonattainment or interfere with 

maintenance of the 2015 8-hour ozone 

NAAQS in any other state. 

III. Proposed Actions 

EPA is proposing to disapprove the 

2015 ozone good neighbor interstate 

transport SIP revisions from Alabama, 

dated August 20, 2018; from 

Mississippi, dated September 3, 2019; 

and from Tennessee, dated September 

13, 2018. Under CAA section 110(c)(1), 

if finalized, these disapprovals would 

establish a 2-year deadline for EPA to 

promulgate a FIP for Alabama, 

Mississippi, and Tennessee to address 

the CAA section 110(a)(2)(D)(i)(I) 

interstate transport requirements 

pertaining to significant contribution to 

nonattainment and interference with 

maintenance of the 2015 8-hour ozone 

NAAQS in other states, unless EPA 

approves a SIP that meets these 

requirements. However, under the CAA, 

a good neighbor SIP disapproval does 

not start a mandatory sanctions clock. 

IV. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

These proposed actions are not 

significant regulatory actions and were 

therefore not submitted to the Office of 

Management and Budget for review. 

B. Paperwork Reduction Act (PRA) 

These proposed actions do not impose 

an information collection burden under 

the PRA because they do not contain 

any information collection activities. 

C. Regulatory Flexibility Act (RFA) 

These actions merely propose to 

disapprove SIP submissions as not 

meeting the CAA for Alabama, 

Mississippi, and Tennessee. EPA 

certifies that these proposed rules will 

not have a significant economic impact 

on a substantial number of small entities 

under the RFA (5 U.S.C. 601 et seq.) 

D. Unfunded Mandates Reform Act 

(UMRA) 

These proposed actions do not 

contain any unfunded mandate as 

described in UMRA, 2 U.S.C. 1531– 

1538, and do not significantly or 

uniquely affect small governments. 

These proposed actions impose no 

enforceable duty on any state, local, or 

tribal governments or the private sector. 

E. Executive Order 13132: Federalism 

These proposed actions do not have 

federalism implications. They will not 

have substantial direct effects on the 

states, on the relationship between the 

national government and the states, or 

on the distribution of power and 

responsibilities among the various 

levels of government. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

These proposed actions do not have 

tribal implications as specified in 

Executive Order 13175. These proposed 

actions do not apply on any Indian 

reservation land, any other area where 

EPA or an Indian tribe has demonstrated 

that a tribe has jurisdiction, or nonreservation areas of Indian country. 

Thus, Executive Order 13175 does not 

apply to these actions. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

EPA interprets Executive Order 13045 

as applying only to those regulatory 

actions that concern environmental 

health or safety risks that EPA has 

reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive Order. These proposed 

actions are not subject to Executive 

Order 13045 because they merely 

propose to disapprove SIP submissions 

from Alabama, Mississippi, and 

Tennessee as not meeting the CAA. 

H. Executive Order 13211, Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

These proposed actions are not 

subject to Executive Order 13211, 

because they are not significant 

regulatory actions under Executive 

Order 12866. 

I. National Technology Transfer and 

Advancement Act 

This proposed rulemaking does not 

involve technical standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

EPA believes the human health or 

environmental risk addressed by these 

proposed actions will not have potential 

disproportionately high and adverse 

human health or environmental effects 

on minority, low-income or indigenous 

populations. These proposed actions 

merely propose to disapprove SIP 

submissions as not meeting the CAA. 

K. CAA Section 307(b)(1) 

Section 307(b)(1) of the CAA governs 

judicial review of final actions by EPA. 

This section provides, in part, that 

petitions for review must be filed in the 

D.C. Circuit: (i) When the agency action 

consists of ‘‘nationally applicable 

regulations promulgated, or final actions 

taken, by the Administrator,’’ or (ii) 

when such action is locally or regionally 

applicable, if ‘‘such action is based on 

a determination of nationwide scope or 

effect and if in taking such action the 

Administrator finds and publishes that 

such action is based on such a 

determination.’’ For locally or regionally 

applicable final actions, the CAA 

reserves to EPA complete discretion 

whether to invoke the exception in 

(ii).61

EPA anticipates that this proposed 

rulemaking, if finalized, would be 

‘‘nationally applicable’’ within the 

meaning of CAA section 307(b)(1) 

because it would take final action on 

SIP submittals for the 2015 8-hour 

ozone NAAQS for the states of Alabama, 

Mississippi, and Tennessee, which are 

located in three different Federal 

judicial circuits (the Eleventh Circuit, 

the Fifth Circuit, and the Sixth Circuit, 

respectively). It would apply uniform, 

nationwide analytical methods, policy 

judgments, and interpretation with 

respect to the same CAA obligations, 

i.e., implementation of good neighbor 

requirements under CAA section 

110(a)(2)(D)(i)(I) for the 2015 8-hour 

ozone NAAQS for states across the 

country, and final action would be 

based on this common core of 

determinations, described in further 

detail below. 

If EPA takes final action on this 

proposed rulemaking, in the alternative, 

the Administrator intends to exercise 

the complete discretion afforded to him 

under the CAA to make and publish a 

finding that the final action (to the 

extent a court finds the action to be 

locally or regionally applicable) is based 

on a determination of ‘‘nationwide 

scope or effect’’ within the meaning of 

CAA section 307(b)(1). Through this 


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9562 Federal Register / Vol. 87, No. 35 / Tuesday, February 22, 2022 / Proposed Rules 

62A finding of nationwide scope or effect is also 

appropriate for actions that cover states in multiple 

judicial circuits. In the report on the 1977 

Amendments that revised section 307(b)(1) of the 

CAA, Congress noted that the Administrator’s 

determination that the ‘‘nationwide scope or effect’’ 

exception applies would be appropriate for any 

action that has a scope or effect beyond a single 

judicial circuit. See H.R. Rep. No. 95–294 at 323, 

324, reprinted in 1977 U.S.C.C.A.N. 1402–03. 

63EPA may take a consolidated, single final 

action on all of the proposed SIP disapproval 

actions with respect to obligations under CAA 

section 110(a)(2)(D)(i)(I) for the 2015 8-hour ozone 

NAAQS. Should EPA take a single final action on 

all such disapprovals, this action would be 

nationally applicable, and EPA would also 

anticipate, in the alternative, making and 

publishing a finding that such final action is based 

on a determination of nationwide scope or effect. 

rulemaking action (in conjunction with 

a series of related actions on other SIP 

submissions for the same CAA 

obligations), EPA interprets and applies 

section 110(a)(2)(d)(i)(I) of the CAA for 

the 2015 8-hour ozone NAAQS based on 

a common core of nationwide policy 

judgments and technical analysis 

concerning the interstate transport of 

pollutants throughout the continental 

U.S. In particular, EPA is applying here 

(and in other proposed actions related to 

the same obligations) the same, 

nationally consistent 4-step framework 

for assessing good neighbor obligations 

for the 2015 8-hour ozone NAAQS. EPA 

relies on a single set of updated, 2016- 

base year photochemical grid modeling 

results of the year 2023 as the primary 

basis for its assessment of air quality 

conditions and contributions at Steps 1 

and 2 of that framework. Further, EPA 

proposes to determine and apply a set 

of nationally consistent policy 

judgments to apply the 4-step 

framework. EPA has selected a 

nationally uniform analytic year (2023) 

for this analysis and is applying a 

nationally uniform approach to 

nonattainment and maintenance 

receptors and a nationally uniform 

approach to contribution threshold 

analysis.62 For these reasons, the 

Administrator intends, if this proposed 

action is finalized, to exercise the 

complete discretion afforded to him 

under the CAA to make and publish a 

finding that this action is based on one 

or more determinations of nationwide 

scope or effect for purposes of CAA 

section 307(b)(1).63

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Ozone. 

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

Dated: February 3, 2022. 

Daniel Blackman, 

Regional Administrator, Region 4. 

[FR Doc. 2022–02948 Filed 2–18–22; 8:45 am] 

BILLING CODE 6560–50–P 


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