Federal Register / Vol. 87, No. 35 / Tuesday, February 22, 2022 / Proposed Rules 9533 

66 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. 

67A 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. 

68The 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. 

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).66

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 8-hour 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.67

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).68

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 7, 2022 

Diana Esher, 

Acting Regional Administrator, Region III. 

[FR Doc. 2022–02952 Filed 2–18–22; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

EPA–R07–OAR–2021–0851; EPA–HQ–OAR– 

2021–0663; FRL–9425–01–R7] 

Air Plan Disapproval; Missouri 

Interstate Transport of Air Pollution for 

the 2015 8-Hour Ozone National 

Ambient Air Quality Standards 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: Pursuant to the Federal Clean 

Air Act (CAA or the Act), the 

Environmental Protection Agency (EPA) 

is proposing to disapprove a State 

Implementation Plan (SIP) submittal 

from Missouri regarding interstate 

transport for the 2015 8-hour ozone 

national ambient air quality standards 

(NAAQS). The ‘‘good neighbor’’ or 

‘‘interstate transport’’ provision requires 

that each state’s SIP 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. This 

disapproval, if finalized, will establish a 

2-year deadline for the EPA to 

promulgate a Federal Implementation 

Plan (FIP) to address the relevant 

interstate transport requirements, unless 

the EPA approves a subsequent SIP 

submittal that meets these requirements. 

Disapproval does not start a mandatory 

sanctions clock. 

DATES: Written comments must be 

received on or before April 25, 2022. 

ADDRESSES: You may send comments, 

identified as Docket No. EPA–R07– 

OAR–2021–0851, by any of the 

following methods: Federal 

eRulemaking Portal at https:// 


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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. 

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 (Aug. 8, 

2011). 

5Cross-State Air Pollution Rule Update for the 

2008 Ozone NAAQS, 81 FR 74504 (Oct. 26, 2016). 

6 In 2019, the D.C. Circuit Court of Appeals 

remanded the 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 

www.regulations.gov following the 

online nstructions for submitting 

comments or via email to 

stone.william@epa.gov. Include Docket 

ID No. EPA–R07–OAR–2021–0851 in 

the subject line of the message. 

Instructions: All submissions received 

must include the Docket ID No. for this 

rulemaking. Comments received may be 

posted without change to https://

www.regulations.gov/, including any 

personal information provided. For 

detailed instructions on sending 

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 

our staff, the EPA Docket Center and 

Reading Room are open to the public by 

appointment only to reduce the risk of 

transmitting COVID–19. Our 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 us online at https://www.epa.gov/ 

dockets. 

FOR FURTHER INFORMATION CONTACT: 

William Stone, Environmental 

Protection Agency, Region 7 Office, Air 

Quality Planning Branch, 11201 Renner 

Boulevard, Lenexa, Kansas 66219; 

telephone number: (913) 551–7714; 

email address: stone.william@epa.gov. 

SUPPLEMENTARY INFORMATION: Public 

participation: Submit your comments, 

identified by Docket ID No. EPA–R07– 

OAR–2021–0851, at https://

www.regulations.gov (our preferred 

method), or the other methods 

identified in the ADDRESSES section. 

Once submitted, comments cannot be 

edited or removed from the docket. The 

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. The EPA will generally not 

consider comments or comment 

contents located outside of the primary 

submission (i.e., on the web, cloud, or 

other file sharing system). 

There are two dockets supporting this 

action, EPA–R07–OAR–2021–0851 and 

EPA–HQ–OAR–2021–0663. Docket No. 

EPA–R07–OAR–2021–0851 contains 

information specific to Missouri, 

including the 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–R07–OAR–2021– 

0851. For additional submission 

methods, please contact William Stone, 

(913) 551–7714, stone.william@epa.gov. 

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-epa-dockets. Due to public 

health concerns related to COVID–19, 

the EPA Docket Center and Reading 

Room are open to the public by 

appointment only. Our 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 us online at https://

www.epa.gov/dockets. 

The EPA continues to carefully and 

continuously monitor information from 

the Centers for Disease Control and 

Prevention (CDC), local area health 

departments, and our Federal partners 

so that we can respond rapidly as 

conditions change regarding COVID–19. 

The index to the docket for this 

action, Docket No. EPA–R07–OAR– 

2021–0851, is available electronically at 

www.regulations.gov. While all 

documents in the docket are listed in 

the index, some information may not be 

publicly available due to docket file size 

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

Throughout this document, ‘‘we,’’ 

‘‘us,’’ and ‘‘our’’ means the EPA. 

I. Background 

A. Description of Statutory Background 

On October 1, 2015, the 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 ‘‘interstate 

transport’’ or ‘‘good neighbor’’ 

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 interstate 

transport of pollution. There are two socalled ‘‘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). The 

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 the EPA’s Four Step 

Interstate Transport Regulatory Process 

The EPA is using the 4-step interstate 

transport framework (or 4-step 

framework) to evaluate the state’s SIP 

submittals addressing the interstate 

transport provision for the 2015 8-hour 

ozone NAAQS. The 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 and the Cross-State Air 

Pollution Rule Update (CSAPR 

Update) 5 and the Revised CSAPR 

Update, both of which addressed the 

2008 ozone NAAQS.6


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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 the 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 the 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). 

9 82 FR at 1735. 

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, available in the 

docket ID No. EPA–HQ–OAR–2021–0663. 

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 ID No. EPA– 

HQ–OAR–2021–0663. 

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.’’ 

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, available in docket ID 

No. EPA–HQ–OAR–2021–0663. 

14The results of this modeling, as well as the 

underlying modeling files, are included in docket 

ID No. EPA–HQ–OAR–2021–0663. 

15See 85 FR 68964, 68981. 

16See the Air Quality Modeling Technical 

Support Document for the Final Revised Cross-State 

Air Pollution Rule Update, included in the 

Headquarters docket ID 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. 

18See Technical Support Document (TSD) 

Preparation of Emissions Inventories for the 2016v2 

North American Emissions Modeling Platform 

Continued 

Through the development and 

implementation of the CSAPR 

rulemakings and prior regional 

rulemakings pursuant to the interstate 

transport provision,7 the 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 the EPA’s Ozone 

Transport Modeling Information 

The EPA has released several 

documents containing information 

relevant to evaluating interstate 

transport with respect to the 2015 8- 

hour ozone NAAQS. First, on January 6, 

2017, the EPA published a notice of data 

availability (NODA) in which we 

requested comment on preliminary 

interstate ozone transport data including 

projected ozone design values (DVs) and 

interstate contributions for 2023 using a 

2011 base year platform.8 In the NODA, 

the 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, we 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, we issued a memorandum (March 

2018 memorandum) noting that the 

same 2023 modeling data released in the 

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 The 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 

Step 1 of the 4-step interstate transport 

framework.13

Since the release of the modeling data 

shared in the March 2018 

memorandum, the EPA performed 

updated modeling using a 2016-based 

emissions modeling platform (i.e., 

2016v1). This emissions platform was 

developed under the EPA/MultiJurisdictional Organization (MJO)/state 

collaborative project.14 This 

collaborative project was a multi-year 

joint effort by the EPA, MJOs, and states 

to develop a new, more recent emissions 

platform for use by the EPA and states 

in regulatory modeling as an 

improvement over the dated 2011-based 

platform that the EPA had used to 

project ozone design values and 

contribution data provided in the 2017 

and 2018 memoranda. The EPA used 

the 2016v1 emissions to project ozone 

DVs and contributions for 2023. On 

October 30, 2020, in the Notice of 

Proposed Rulemaking for the Revised 

CSAPR Update, the EPA released and 

accepted public comment on 2023 

modeling that used the 2016v1 

emissions platform.15 See 85 FR 68964, 

68981. 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 

ozone NAAQS.16

Following the Revised CSAPR Update 

final rule, the EPA made further updates 

to the 2016 emissions platform to 

include mobile emissions from the 

EPA’s Motor Vehicle Emission 

Simulator MOVES3 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 emissions modeling 

technical support document (TSD) for 

this proposed rule.18 The EPA 


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included in the Headquarters docket ID No. EPA– 

HQ–OAR–2021–0663. 

19Ramboll Environment and Health, January 

2021, www.camx.com. 

20March 2018 memorandum, Attachment A. 

21 Id. at A–1. 

22 Id. 

23For 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 

Aug. 3, 2018). 

performed air quality modeling of the 

2016v2 emissions using the most recent 

public release version of the 

Comprehensive Air Quality Model with 

Extensions (CAMx) photochemical 

modeling, version 7.10. with the 2016 

base year and 2023 future year 

emissions developed as part of the 

2016v2 emissions platform.19 The EPA 

now proposes to rely on modeling based 

on the updated and newly available 

2016v2 air quality modeling in 

evaluating these submissions with 

respect to Steps 1 and 2 of the 4-step 

interstate transport framework. By using 

the updated modeling results, the EPA 

is using the most current and 

technically appropriate information for 

this proposed rulemaking. Section III of 

this document and the Air Quality 

Modeling TSD included in the docket 

for this proposal contain additional 

detail on the modeling performed using 

the 2016v2 emissions. In this document, 

the EPA is accepting public comment on 

this updated 2023 modeling, which uses 

a 2016 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 Ozone NAAQS 

Transport SIP Proposed Actions. 

Comments on the EPA’s air quality 

modeling should be submitted in the 

Regional docket for this action, docket 

ID No. EPA–R07–OAR–2021–0851. 

Comments are not being accepted in 

docket EPA–HQ–OAR–2021–0663. 

States may have chosen to rely on the 

results of the 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 III we evaluate 

how Missouri used air quality modeling 

information in their submission. 

D. The EPA’s Approach to Evaluating 

Interstate Transport SIPs for the 2015 8- 

Hour Ozone NAAQS 

The 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 the CSAPR and 

related rulemakings. Nationwide 

consistency in approach is particularly 

important in the context of interstate 

ozone transport, which is a regionalscale 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, the 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. 

The 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, the 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 ‘‘flexibilities’’ as may 

have been identified or suggested in the 

past, the EPA will evaluate whether the 

state adequately justified the technical 

and legal basis for doing so. 

The EPA notes that certain 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 

ozone NAAQS. Attachment A to the 

March 2018 memorandum identified a 

‘‘Preliminary List of Potential 

Flexibilities’’ that could potentially 

inform SIP development.20 However, 

the 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 the EPA sought 

‘‘feedback from interested 

stakeholders.’’ 21 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 are we 

specifically recommending that states 

use these approaches.’’ 22 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, the 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 the EPA 

must implement the interstate transport 

provision in a manner ‘‘consistent with 

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

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).23 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). 

938 F.3d at 313. 

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

issued a decision in Maryland v. EPA 

that cited the Wisconsin decision in 

holding that the 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 the 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 


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24We note that the court in Maryland did not 

have occasion to evaluate circumstances in which 

the 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. 

25See 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 Aug. 3, 2018). 

26See North Carolina v. EPA, 531 F.3d 896, 910– 

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

‘‘independent significance’’ to each prong of CAA 

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

27See 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). 

28See 76 FR 48208 (August 8, 2011). CSAPR 

Update and Revised CSAPR Update also used this 

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

86 FR 23054 (April 30, 2021). 

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). The 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,24 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, 2024.25 The 

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. 

The 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 the 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, the EPA must act on 

SIP submittals using the information 

available at the time it takes such action. 

In this circumstance, the 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 23074; see also 

Wisconsin, 938 F.3d at 322. 

Consequently, in this proposal the 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, the EPA identifies 

monitoring sites that are projected to 

have problems attaining and/or 

maintaining the NAAQS in the 2023 

analytic year. Where the 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 

the EPA’s 4-step interstate transport 

framework. For sites that are identified 

as a nonattainment or maintenance 

receptor in 2023, we proceed to the next 

step of our 4-step interstate transport 

framework by identifying the upwind 

state’s contribution to those receptors. 

The EPA’s approach to identifying 

ozone nonattainment and maintenance 

receptors in this action is consistent 

with the approach used in previous 

transport rulemakings. The 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.26

For the purpose of this proposal, the 

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 the EPA defined 

nonattainment receptors as those areas 

that both currently measure 

nonattainment and that the EPA projects 

will be in nonattainment in the future 

analytic year (i.e., 2023).27

In addition, in this proposal, the EPA 

identifies a receptor to be a 

‘‘maintenance’’ receptor for purposes of 

defining interference with maintenance, 

consistent with the method used in the 

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).28 Specifically, the 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. The 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). The 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. Consistent with 

the methodology described for 

nonattainment, those sites that are 


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29As 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, the EPA has 

developed emissions inventories, analyzed different 

levels of control stringency at different cost 

thresholds, and assessed resulting downwind air 

quality improvements. 

currently measuring ozone 

concentrations below the level of the 

applicable NAAQS, but that are 

projected to be nonattainment based on 

the average or maximum design values, 

are identified as maintenance-only 

receptors. 

3. Step 2 of the 4-Step Interstate 

Transport Framework 

In Step 2, the 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 the 

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). 

The 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 the 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. The EPA continues 

to find 1 percent to be an appropriate 

threshold. For ozone, as the EPA found 

in the Clean Air Interstate Rule (CAIR), 

CSAPR, and CSAPR Update, portion of 

the nonattainment problems from 

anthropogenic sources in the U.S. 

results 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. The 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 the 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)). 

The 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, 

the 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. 

4. Step 3 of the 4-Step Interstate 

Transport Framework 

Consistent with the 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. The 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 the 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 emissions-reducing 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 welldocumented evaluation determining 

whether their emissions constitute 

significant contribution or interference 

with maintenance by evaluating 

additional available control 

opportunities by preparing a multifactor 

assessment. While the EPA has not 

prescribed a particular method for this 

assessment, the 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 

additional emissions controls should be 

required.29

5. Step 4 of the 4-Step Interstate 

Transport Framework 

At Step 4, states (or the 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 SIP 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 

110(a)(2)(A); Committee for a Better 

Arvin v. U.S. E.P.A., 786 F.3d 1169, 

1175–76 (9th Cir. 2015) (holding that 

measures relied on by state to meet CAA 

requirements must be included in the 

SIP). 

II. SIP Submission Addressing 

Interstate Transport of Air Pollution for 

the 2015 8-Hour Ozone NAAQS 

On June 10, 2019, the Missouri 

Department of Natural Resources’ Air 

Pollution Control Program (MoDNR) 


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made a SIP submission to address 

interstate transport of air pollution for 

the 2015 8-hour ozone NAAQS. 

MoDNR’s good neighbor SIP submission 

for the 2015 ozone NAAQS relied on the 

EPA’s four-step approach and 

corresponding memoranda for 

determining obligations for upwind 

states to limit transported air pollution 

to downwind states. The State 

concluded that emissions from sources 

or emissions activity in Missouri will 

not contribute significantly to 

nonattainment or interfere with 

maintenance of the 2015 ozone NAAQS 

in any downwind states. 

In its analysis, the state relied on the 

EPA’s modeling released with the 

March 2018 memorandum to identify 

nonattainment and maintenance 

receptors in 2023 (Step 1). The State 

also relied on the EPA’s modeling from 

the March 2018 memorandum to 

identify which monitors were then 

linked to emissions from Missouri. In its 

submission, the MoDNR identified all of 

the nonattainment and maintenance 

receptors to which Missouri was 

projected to contribute more than 0.70 

ppb to the 2023 DV. Table 1 provides 

information on the six nonattainment 

and maintenance receptors identified by 

the MoDNR. 

TABLE 1—2023 AVERAGE AND MAXIMUM DESIGN VALUES AT DOWNWIND RECEPTORS WITH MISSOURI CONTRIBUTIONS

LARGER THAN 0.70 PPB

Site 

(monitor, county, state) 

2023 

Average DV 

(ppb) 

2023 

Maximum DV 

(ppb) 

Missouri 

contribution 

(ppb) 

Comments 

260050003, Allegan, MI .................................................................. 69.0 71.7 2.61 Maintenance receptor. 

261630019, Wayne, MI ................................................................... 69.0 71.0 0.92 Maintenance receptor. 

484392003, Brazoria, TX ................................................................ 74.0 74.9 0.88 Nonattainment receptor. 

482011039, Harris, TX .................................................................... 71.8 73.5 0.88 Nonattainment receptor.

550790085 Milwaukee, WI .............................................................. 71.2 73.0 0.93 Nonattainment receptor. 

551170006, Sheboygan, WI ............................................................ 72.8 75.1 1.37 Nonattainment receptor. 

The state analyzed each of the six 

receptors in Table 1 using information 

in the EPA’s 2018 guidance memoranda 

described above. For the two receptors 

in Texas, the state observed that the 

total upwind state contribution is 

approximately 13 ppb to both of these 

Texas receptors and that Texas’ in-state 

contribution to these two receptors is 26 

ppb to the Brazoria County receptor and 

22.6 ppb to the Harris County receptor. 

The MoDNR combined the 

contributions from initial/boundary 

conditions with the contribution from 

biogenic emissions to show that the 

contribution from these two categories 

is over 52 ppb, at these two receptors. 

Based on this information, the MoDNR 

claimed that the ozone problems at 

these two receptors are not caused by 

upwind U.S. anthropogenic emissions 

from other states, but rather that in-state 

contributions, natural ozone 

concentrations, and international 

emissions are the likely significant 

contributors to the problem at these two 

sites. 

The MoDNR also noted that its 

contribution to the projected 2023 ozone 

DV at the two Texas receptors is 0.88 

ppb. The MoDNR then referenced 

statements in the EPA’s August 2018 

memorandum on the use of alternative 

thresholds that a 1 ppb threshold would 

generally capture a substantial amount 

of transported contribution from 

upwind states to the downwind 

monitors. The MoDNR concluded that 1 

ppb is, therefore, an appropriate 

alternative screening threshold for 

evaluating whether emissions in their 

state are linked to the ozone problems 

at these two receptors. Based on this 

alternative threshold, the State 

determined that it will not contribute 

significantly to these nonattainment 

receptors in 2023. The MoDNR then 

concluded that its SIP sufficiently 

addresses the good neighbor obligation 

for the 2015 ozone NAAQS with respect 

to these two Texas receptors based only 

on its Step 2 weight of evidence 

analysis. 

For the Milwaukee, Wisconsin 

receptor, the MoDNR noted that its 

projected contribution to this receptor is 

0.93 ppb, and thus less than 1 ppb. The 

State observed that the 1 ppb threshold 

would capture 79.4 percent of the total 

contribution from all upwind states and 

that the contribution captured by the 1 

ppb threshold is 83 percent of the 

amount captured by the 0.70 ppb 

threshold at this receptor. The state 

asserted that the 1 ppb threshold would 

capture a substantial amount of total 

upwind states’ contribution to ozone 

concentrations at this receptor, which 

will lead to meaningful emission 

reductions to ensure attainment of the 

NAAQS at this monitor in 2023. 

Therefore, the MoDNR relied on a 1 ppb 

threshold to conclude that its existing 

SIP sufficiently addresses the good 

neighbor obligation for the 2015 ozone 

NAAQS with respect to this receptor. 

For the Wayne, Michigan site, the 

state observed that the 1 ppb threshold 

captures 61.8 percent of total upwind 

state contributions and the contribution 

captured by the 1 ppb threshold would 

constitute 92.2 percent of the total 

contribution that would be captured by 

the 0.70 ppb threshold. The state 

asserted that the 1 ppb threshold will 

capture a substantial amount of upwind 

states’ contribution to the ozone 

concentrations at this site, which will 

lead to meaningful emission reductions 

that will help ensure attainment of the 

NAAQS at this receptor in 2023. The 

MoDNR noted that its projected 

contribution to the Wayne, Michigan 

receptor is 0.92 ppb, and thus less than 

1 ppb. Therefore, the MoDNR concluded 

that its existing SIP sufficiently 

addresses the good neighbor obligation 

for the 2015 ozone NAAQS with respect 

to this receptor based only on this Step 

2 weight of evidence analysis. 

For the Sheboygan, Wisconsin site, 

the State observed that the 1 ppb 

threshold would capture 79.4 percent of 

the total upwind contributions and that 

a 2 ppb threshold would capture 68.2 

percent of the total upwind state 

contributions. The State also observed 

that an alternative 2 ppb threshold 

would capture 85.9 percent of the 

upwind state contributions captured 

under a 1 ppb threshold. Using these 

data, the MoDNR asserted that a 2 ppb 

threshold is appropriate because it 

would capture nearly 70 percent of the 

total upwind state contributions and 

thus would result in meaningful 

emission reductions that will help to 

ensure attainment of the NAAQS at the 

site by 2023. The state also asserted that 

the primary contributors to the 

projected ozone concentrations at the 

monitor in Sheboygan include 

emissions from Illinois, Indiana, and 

Wisconsin. The MoDNR cited the EPA 

modeling projecting that emissions from 

these states would contribute a 


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9540 Federal Register / Vol. 87, No. 35 / Tuesday, February 22, 2022 / Proposed Rules 

30 Interstate Transport Modeling for the 2015 

Ozone National Ambient Air Quality Standard, the 

technical support document (TSD), https://

www.ladco.org/wp-content/uploads/Documents/ 

Reports/TSDs/O3/LADCO_2015O3iSIP_TSD_

13Aug2018.pdf. 

combined 31.93 ppb in 2023 to the 

Sheboygan receptor. 

For the Sheboygan receptor, the 

MoDNR also pointed to the Lake 

Michigan Air Director’s Consortium’s 

(LADCO’s) interstate transport modeling 

results for the 2015 ozone NAAQS. The 

State noted that LADCO’s analysis also 

indicates that the ozone levels at the 

Wisconsin shoreline of Lake Michigan 

are heavily affected by the emissions 

from Illinois, Indiana, and Wisconsin.30

The MoDNR further pointed out that 

the other monitoring site in Sheboygan 

County (551170009), which is a few 

miles further inland than the Sheboygan 

nonattainment receptor, has no 

projected problems with attaining and 

maintaining compliance with the 2015 

ozone NAAQS. The MoDNR concluded 

that the nonattainment receptor in 

Sheboygan is heavily influenced by 

local transport emissions and lake 

breeze effects over Lake Michigan. The 

State asserted that use of a 2 ppb 

threshold would capture a substantial 

amount of upwind states’ contribution 

to the ozone concentrations at this site, 

which will lead to meaningful emission 

reductions that will help ensure 

attainment of the NAAQS at this 

monitor in 2023. The MoDNR noted that 

its projected contribution to the 

Sheboygan, Wisconsin receptor is 1.37 

ppb, which is less than 2 ppb. 

Therefore, the MoDNR concluded that 

its existing SIP sufficiently addresses 

the good neighbor obligation for the 

2015 ozone NAAQS with respect to the 

Sheboygan receptor based only on this 

Step 2 weight of evidence analysis. 

For the Allegan, Michigan receptor, 

the MoDNR used an analysis based on 

information in the EPA’s October 2018 

memorandum on alternative approaches 

for identifying maintenance receptors to 

claim that the Allegan monitoring site 

will not be a receptor in 2023. 

Specifically, rather than rely upon the 

EPA’s projected 2023 maximum design 

value for identifying maintenance 

receptors, the state used an alternative 

approach that included projected 2023 

ozone concentrations based on a 2-year 

base period (2010–2011), a 3-year base 

period (2009–2011) and a 4-year base 

period (2009–2012) to demonstrate that 

the Allegan monitoring site would attain 

the standard by 2023. To support the 

use of these alternative base periods, the 

State provided an analysis for the three 

consideration outlined in the August 

2018 memorandum: (i) Meteorological 

conditions in the area of the monitoring 

site were conducive to ozone formation 

during the alternative base period 

design value used for projections; (ii) 

ozone concentrations have been 

trending downward at the site since 

2011 (and ozone precursor emissions of 

NOX and VOCs have also decreased); 

and (iii) emissions are expected to 

continue to decline in the upwind and 

downwind states out to the attainment 

date of the site. The MoDNR noted that 

ozone concentrations during the 

summer of 2009 were well below 

normal for the state of Michigan despite 

having a large number of days during 

the ozone season where they claim that 

meteorology was conducive to ozone 

formation. The MoDNR also noted that 

the summer of 2012 was among the 

most ozone conducive summers across 

the entire Midwestern portion of the 

country. MoDNR suggested that the 

variation in the degree of ozone 

conducive meteorology between 2009 

and 2012 would counterbalance in the 

alternative baseline period. 

The State provided an analysis 

showing ozone concentrations trending 

down since 2012 at the Allegan monitor. 

The State also provided the total 

statewide anthropogenic NOX and VOC 

emissions (ozone precursors) in 

Michigan, Missouri, and two 

neighboring states that are upwind of 

the Allegan monitor during 2011 and 

2017 (i.e., Illinois and Indiana), which 

showed that emissions in all four of 

these states went down during this time 

period. 

The MoDNR concluded that the 

Allegan receptor meets all the criteria 

listed in the EPA October memorandum 

relating to alternative methods for 

identifying maintenance receptors. 

Based on this analysis, the MoDNR 

asserted that the Allegan Michigan 

monitor should not be a maintenance 

receptor for purposes of the 2015 ozone 

NAAQS. Therefore, the State found that 

the Missouri’ existing SIP fully 

addresses the CAA good neighbor 

obligation with respect to the Allegan, 

Michigan receptor. 

Based on the analysis above, the 

MoDNR concluded that its current SIP 

adequately addresses the state’s 

obligation under CAA section 

110(a)(2)(D)(i)(I) (the good neighbor 

provision) with respect to the 2015 

ozone NAAQS. The MoDNR stated that 

it has demonstrated that its SIP 

submittal ensures that emissions in 

Missouri will not significantly 

contribute to nonattainment or interfere 

with maintenance of the 2015 ozone 

NAAQS in any downwind state. Based 

on this conclusion, the MoDNR 

concluded its analysis at Step 2 of the 

4-step interstate transport framework 

and provided no analysis for steps 3 or 

4. 

III. EPA Evaluation 

The EPA is proposing to find that the 

June 10, 2019, SIP submission from the 

MoDNR 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 the 

EPA’s evaluation of the SIP submission 

using the 4-step interstate transport 

framework, and the EPA is therefore 

proposing to disapprove Missouri’s 

submission. 

A. Missouri 

1. Evaluation of Information Provided 

by the MoDNR Regarding Step 1 

At Step 1 of the 4-Step interstate 

transport framework, the MoDNR relied 

on the EPA modeling released in the 

March 2018 memorandum to identify 

nonattainment and maintenance 

receptors in 2023. As correctly noted in 

the MoDNR SIP submittal, the EPA’s 

prior analysis indicated that the State 

was linked to six nonattainment and/or 

maintenance receptors in three 

downwind states in 2023 (identified in 

Table 1 of this action). In its October 

2018 memorandum on alternative 

maintenance receptors, the EPA 

suggested that States could provide 

meteorological data, among other data, 

to support potential alternative 

methodologies or flexibilities to identify 

maintenance receptors. The MoDNR 

utilized this flexibility to eliminate the 

Allegan, Michigan maintenance receptor 

(monitor ID 260050003) based on the 

use of alternative base year periods. The 

State considered three alternative base 

periods as a basis for projecting design 

values in 2023. These based periods 

include (1) a 2-year base period using 

4th high ozone concentrations in 2010 

and 2011, (2) a 3-year base year period 

from 2009–2011, and (3) a 4-year base 

year period from 2009–2012. As an 

initial matter, design values, by 

definition are based on the average of 

the 4th highest maximum daily 8-hour 

ozone concentration in three 

consecutive years. The ‘‘pseudo’’ design 

values calculated by the State using 2 

years of data, when data for the third 

year (i.e., 2009) were clearly available, 

and using 4 years of data do not 

constitute alternative design values. In 

this regard, the approach by the State 

using these two alternatives runs 

counter to the approach identified in the 

October 2018 memorandum: ‘‘. . . . 

EPA believes that a state may, in some 


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cases, use a design value from the base 

period that is not the maximum design 

value.’’ 

The State also provided information 

and analysis of meteorological data to 

attempt to establish that all years that 

constitute the 2011 design value (i.e., 

the average of the 4th high values in 

2009, 2010, and 2011) were conducive 

to ozone formation. The State’s analysis 

noted that the summer of 2009 was well 

below normal for average temperatures, 

but highlighted that data from Western 

Michigan Regional Airport national 

weather service site showed that a 

number of days in summer of 2009 were 

conducive to ozone formation. Overall, 

the state identified 25 days between 

May and September of 2009 that it 

considered conducive to ozone 

formation based on the criteria that the 

temperature reached 80 degrees 

Fahrenheit or greater, no precipitation 

occurred, and the daily average wind 

speed was less than 5 miles per hour. In 

the EPA’s review, we find the State did 

not sufficiently demonstrate that all 

years within the alternative base period 

were conducive to ozone formation. As 

the State noted, the summer of 2009 was 

abnormally cool in Michigan. While the 

State also analyzed local meteorological 

data (temperature, precipitation, wind 

speed) near the Allegan, Michigan 

monitor to identify 25 days that it 

considered conducive to ozone 

formation based on surface 

temperatures, wind speed and 

precipitation, the State did not provide 

any technical analysis to demonstrate a 

statistically significant relationship 

between high ozone concentrations at 

the Allegan receptor and the 

temperature, precipitation, and wind 

speed criteria used in the submittal to 

define ozone conducive conditions for 

this receptor. In addition, the State’s 

evaluation 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 2009. The supplemental information 

provided in the October 2018 

memorandum, which included 

temperature anomalies by state and 

region of the U.S. and annual state-wide 

average June–August temperature 

rankings, clearly highlight that the 

summer of 2009 was abnormally cool in 

Michigan and the Great Lakes Region. 

Therefore, the EPA finds that not all 

years within the alternative base period 

used by the State (i.e., 2009–2011) were 

conducive to ozone formation, 

especially given the abnormally cold 

temperatures seen in the summer of 

2009. Accordingly, in view of the 

guidance included in the October 2020 

memorandum, it was not appropriate for 

the state to have eliminated the Allegan, 

Michigan receptor as a maintenance 

receptor at Step 1 of the 4-step interstate 

transport framework on this basis. 

Further, the MoDNR’s attempt to 

eliminate this receptor on the basis of 

this analysis did not provide any basis 

to eliminate the other receptors to 

which the EPA’s modeling suggested the 

state was linked. The EPA’s most recent 

modeling, discussed further in section 

III.A.3, confirms that the existence of 

several receptors to which the state is 

linked. The EPA therefore proposes to 

proceed to evaluate the submittal at 

Step 2. 

2. Evaluation of Information Provided 

by the State Regarding Step 2 

As an initial matter, the EPA disagrees 

with the arguments made by MoDNR 

based on the ostensible ‘‘causation’’ of 

the projected attainment and 

maintenance problems at the receptors 

in Brazoria County and Harris County in 

Texas. While it is correct that impacts 

from various sources, such as in-state 

contributions, background ozone 

concentrations, and international 

emissions, are often themselves 

significant contributors to attainment 

and maintenance problems at receptors 

for the 2015 ozone NAAQS, this does 

not address the question of whether 

there are also interstate transport 

impacts from emissions sources or 

activities in Missouri that significantly 

contribute to nonattainment, or interfere 

with maintenance, in any other state. 

This question is not one of causation, 

but rather of whether there is significant 

contribution as contemplated in CAA 

section 110(a)(2)(D)(i)(I). The EPA’s 4- 

step interstate transport framework is 

intended to evaluate whether there are 

emissions that the State must address in 

its SIP to meet this requirement for 

purposes of the 2015 ozone NAAQS. 

The State also utilized a 1 ppb 

threshold at Step 2 for the receptors in 

Wayne Michigan, Milwaukee, 

Wisconsin and both Texas receptors to 

evaluate whether the state was ‘‘linked’’ 

to a projected downwind nonattainment 

or maintenance receptor. As discussed 

in the EPA’s August 2018 

memorandum, with appropriate 

additional analysis it may be reasonable 

for states to use a 1 ppb contribution 

threshold, instead of the 1 percent of the 

NAAQS threshold for the purposes of 

identifying linkages to appropriate 

downwind receptors. In some cases, 

MoDNR argued for application of the 

alternative 1 ppb threshold, by 

presenting the different numerical 

percentages of downwind impacts that 

the respective thresholds would result 

in, and then asserting that the 

percentages of upwind contribution 

captured from the 1 ppb threshold 

would be sufficiently substantial to 

justify its use for Missouri. 

For the Wayne, Michigan receptor, 

MoDNR observed that application of a 1 

ppb threshold would capture 61.8 

percent of total upwind state 

contributions, and that the contribution 

captured by the 1 ppb threshold would 

constitute 92.2 percent of the total 

contribution that would be captured by 

application of the 0.70 ppb threshold. 

The State thus argued that use of a 1 

ppb threshold instead of a 1% of the 

NAAQS threshold will capture a 

substantial amount of upwind states’ 

contribution to the ozone concentrations 

at this site. Using this alternative 

threshold, MoDNR stated that the 

projected Missouri contribution to the 

Wayne, Michigan receptor is 0.92 ppb, 

and thus less than 1 ppb. MoDNR made 

a comparable argument for the 

Milwaukee, Wisconsin receptor (79.4 

percent of the total contribution from all 

upwind states and that the contribution 

captured by the 1 ppb threshold is 83 

percent of the amount captured by the 

0.70 ppb threshold). For the receptors in 

Brazoria County and Harris County, 

Texas, the MoDNR did not provide any 

additional analyses to determine the 

appropriateness of the application of the 

1 ppb threshold at either of these 

receptors, and simply referred to the 

August 2018 memorandum as evidence 

to support the use of a 1 ppb threshold 

at these receptors. Rather than a 

quantitative comparison, MoDNR made 

qualitative statements to the effect that 

a 1 ppb threshold would be appropriate 

given other considerations, such as the 

impacts of local or international 

sources. 

However, the EPA’s memorandum did 

not indicate that this type of 

information alone was determinative of 

whether an alternative threshold was in 

fact appropriate to justify use of a 

threshold in lieu of the 0.70 ppb level. 

Rather, the EPA 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. The MoDNR 

did not provide any further technical 

justification to make that determination. 

The EPA notes that in each case, the 

use of the alternative 1 ppb threshold 


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31August 2018 memo at 4. 

32Air 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. 

33We note that Congress has placed on the 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. 34See August 2018 memo, at 4. 

would have the result of reducing the 

amount of cumulative upwind state 

emissions that would be captured. 

While the EPA does not, in this action, 

approve of the state’s application of the 

1 ppb threshold, because the state has 

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 would 

not alter our review and proposed 

disapproval of this SIP submittal. 

The 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 at Step 

2.31 However, the EPA also indicated 

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, the 

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 the 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, the EPA expended its own 

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.32 It was at the 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 ozone NAAQS. 

Furthermore, the 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 ozone NAAQS raises 

substantial policy, consistency, and 

practical implementation concerns.33

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 SIP 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 could 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. The EPA recognized in the 

August 2018 memo that there was some 

similarity in the amount of total upwind 

contribution captured (on a nationwide 

basis) between 1percent and 1 ppb. 

However, the 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 seven percent of 

total upwind state contribution was lost 

according to the modeling underlying 

the August 2018 memorandum; 34 in the 

EPA’s updated modeling, the amount 

lost is five 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 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. 

Accord 76 FR 48237–38. 

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, the EPA’s experience 

since the issuance of that memo has 

revealed substantial programmatic and 

policy difficulties in attempting to 

implement this approach. Nonetheless, 

the EPA is not, at this time, rescinding 

the August 2018 memorandum. The 

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, the EPA may 

determine to rescind the August 2018 

memorandum in the future. 

MoDNR used two arguments at Step 

2 for excluding the nonattainment 

receptor in Sheboygan, Wisconsin, 

(Monitor ID: 551170006). First, the State 

utilized a 2 ppb threshold at Step 2 to 

identify whether the state was ‘‘linked’’ 

to this receptor. Second, the state argued 

that any reductions from Missouri 

would have a de minimis or minimal 

effect on air quality improvements at 

this receptor due to the larger impacts 

from other states such as Wisconsin, 


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35Because the EPA finds that the MoDNR 

submittal’s arguments with respect to its linkages in 

the modeling it relied on are not sufficient or 

technically justified to conclude the state is not 

linked to downwind receptors, the EPA can also 

conclude that the same arguments would not be 

meritorious even if applied with respect to the 

receptor linkages the EPA finds in its more recent 

2023 modeling using the 2016v2 emissions 

platform. 

36 Design values and contributions at individual 

monitoring sites nationwide are provide in the file: 

‘‘2016v2_DVs_state_contributions.xlsx’’ which is 

included in docket ID No. EPA–HQ–OAR–2021– 

0663. 

Illinois and Indiana. The EPA discusses 

both of these arguments in this section. 

In its analysis, the state argued that 

because a 2 ppb threshold would 

capture 68.2% of cumulative upwind 

state contributions at the Sheboygan 

receptor, similar to the ‘‘approximately 

70 percent of total upwind 

contribution’’ captured on average 

nationwide at the 1 ppb threshold the 

EPA identified in the August 2018 

memorandum, a 2 ppb threshold is 

appropriate to use at this receptor. 

While the EPA had determined that an 

alternative threshold that would capture 

a sufficient percentage of upwind state 

emissions comparable to the amount 

that would be captured at the level of 1 

percent of the NAAQS may be 

appropriate, the Agency also indicated 

that more analysis would be needed to 

reach a determinative conclusion of 

appropriateness. As explained with 

respect to the alternative 1 ppb 

threshold that MoDNR sought to use for 

the for the receptors in Wayne 

Michigan, Milwaukee, Wisconsin and 

both Texas receptors, it did not provide 

any further technical justification to 

make the determination. 

As explained with respect to the 

potential use of an alternative 1 ppb 

threshold, the EPA’s experience since 

the issuance of the 2018 memorandum 

discussing the issue has revealed 

substantial programmatic and policy 

difficulties in attempting to implement 

this approach even for a 1 ppb 

threshold. At no point did the EPA 

suggest that a 2 ppb threshold might be 

appropriate for this purpose under any 

circumstances. Such a threshold would 

be higher than the threshold that the 

EPA has historically used in interstate 

transport rules that courts have 

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

at issue), or that the EPA has considered 

even potentially appropriate if it were to 

achieve functionally the same air 

quality impacts (i.e., 1 ppb). 

The second argument that the state 

used to exclude the Sheboygan, 

Wisconsin receptor in Step 2 was 

related to emissions from other states. 

The state argued that the primary 

contributors to the projected ozone 

concentrations in Sheboygan are the 

upwind states of Illinois and Indiana 

and the home state itself, Wisconsin. 

The EPA’s 2018 modeling showed these 

states would contribute a combined 

31.93 ppb in 2023 to the Sheboygan 

receptor. However, the state’s reasoning 

related to Indiana, Illinois and 

Wisconsin emissions is inapplicable to 

the requirements of CAA section 

110(a)(2)(D)(i)(I). The good neighbor 

provision requires states and the EPA to 

address interstate transport of air 

pollution that contributes to downwind 

states’ ability to attain and maintain 

NAAQS. Whether emissions from other 

states also contribute to the same 

downwind air quality issue is irrelevant 

in assessing whether a downwind state 

has an air quality problem, or whether 

the upwind state at issue state is 

significantly contributing to that 

problem. The Ozone NAAQS 

nonattainment and maintenance 

problems that result from interstate 

transport are typically the result of 

cumulative impacts from multiple 

states. States are not obligated under 

CAA section 110(a)(2)(D)(i)(I) to reduce 

emissions only if doing so would be 

sufficient in isolation to resolve all 

downwind nonattainment or 

maintenance problems. Rather, each 

state is obligated to eliminate its own 

‘‘significant contribution’’ or 

‘‘interference’’ with the ability of other 

states to attain or maintain the NAAQS. 

Indeed, the D.C. Circuit in Wisconsin 

specifically rejected petitioner 

arguments suggesting that upwind states 

should be excused from good neighbor 

obligations on the basis that some other 

source of emissions (whether 

international or another upwind state) 

could be considered the ‘‘but-for’’ cause 

of downwind air quality problem. 938 

F.3d 303 at 323–324. The court viewed 

petitioners’ arguments as essentially an 

argument ‘‘that an upwind State 

‘contributes significantly’ to downwind 

nonattainment only when its emissions 

are the sole cause of downwind 

nonattainment.’’ 938 F.3d 303 at 324. 

The court explained that ‘‘an upwind 

State can ‘contribute’ to downwind 

nonattainment even if its emissions are 

not the but-for cause.’’ Id. at 324–325. 

See also Catawba County v. EPA, 571 

F.3d 20, 39 (D.C. Cir. 2009) (rejecting 

the argument ‘‘that ‘significantly 

contribute’ unambiguously means 

‘strictly cause’ ’’ because there is ‘‘no 

reason why the statute precludes EPA 

from determining that [an] addition of 

[pollutant] into the atmosphere is 

significant even though a nearby 

county’s nonattainment problem would 

still persist in its absence’’); Miss. 

Comm’n on Envtl. Quality v. EPA, 790 

F.3d 138, 163 n.12 (D.C. Cir. 2015) 

(observing that the argument that ‘‘there 

likely would have been no violation at 

all . . . if it were not for the emissions 

resulting from [another source]’’ is 

‘‘merely a rephrasing of the but-for 

causation rule that we rejected in 

Catawba County.’’). Therefore, a state is 

not excused from eliminating its 

significant contribution on the basis that 

other states’ emissions also contribute 

some amount of pollution to the same 

receptors to which the state is linked. 

As a result, Step 3 analysis of the 4-Step 

Interstate Transport Framework is 

necessary. 

Thus, the EPA proposes that 

MoDNR’s submittal did not adequately 

justify the use of an alternative 

threshold or otherwise establish that it 

should not be considered linked at Step 

2. The EPA proposes to apply the 1 

percent of NAAQS threshold, consistent 

with the discussion in this subsection. 

Under the proposed 1 percent threshold, 

both in the modeling available to the 

state at the time it made its submittal, 

and under the newly available 2023 

modeling discussed below, Missouri is 

linked to downwind nonattainment and 

maintenance receptors.35

3. Results of the EPA’s Step 1 and Step 

2 Modeling and Findings for Missouri 

As described in section I, the EPA 

performed air quality modeling to 

project design values and contributions 

for 2023 using the 2016v2 emissions 

platform. The EPA examined these data 

to determine if emissions in Missouri 

contribute 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 

in this most recent round of modeling. 

As shown in Table 2, the data indicate 

that in 2023, emissions from sources in 

Missouri contribute greater than 1 

percent of the NAAQS to nonattainment 

or maintenance-only receptors in Racine 

County and Kenosha County, 

Wisconsin, and Cook County, Illinois.36

Therefore, based on the EPA’s 

evaluation of the information submitted 

by MoDNR, and based on the EPA’s 

most recent modeling results for 2023, 

the EPA proposes to find that Missouri 

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. 


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TABLE 2—MISSOURI LINKAGE RESULTS BASED ON THE EPA UPDATED 2023 MODELING

Receptor ID Location Nonattainment/maintenance 

2023 Average 

design value 

(ppb) 

2023 Maximum 

design value 

(ppb) 

MO contribution 

(ppb) 

550590025 .......................... Kenosha, Wisconsin ......... Maintenance .......................... 69.2 72.3 1.66 

550590019 .......................... Kenosha, Wisconsin ......... Nonattainment ....................... 72.8 73.7 1.08 

170317002 .......................... Cook, Illinois ...................... Maintenance .......................... 70.1 73.0 0.94 

551010020 .......................... Racine, Wisconsin ............ Nonattainment ....................... 71.3 73.2 0.92 

4. Evaluation of Information Provided 

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 evaluate effectively 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. The 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. 

MoDNR did not conduct such an 

analysis in its SIP submission, as a 

result of its conclusions pursuant to 

Step 1 and Step 2 of its analysis with 

respect to the six receptors that the EPA 

previously identified. As explained in 

connection with the evaluation of 

MoDNR’s Step 1 and Step 2 analyses, 

the EPA disagrees with those analyses 

and accordingly the State should have 

evaluated effectively which emissions 

in the State should be deemed 

‘‘significant’’ and therefore prohibited, 

in its SIP submission. We therefore 

propose that MoDNR was required to 

analyze emissions from the sources and 

other emissions activity from within the 

state to determine whether its 

contributions were significant, and we 

propose to disapprove its submission 

because MoDNR failed to do so. 

5. Evaluation of Information Provided 

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, Missouri’s SIP 

submission 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, the EPA proposes to 

disapprove Missouri’ 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). 

6. Conclusion 

Based on the EPA’s evaluation of the 

MoDNR’s SIP submission, the EPA is 

proposing to find that the MoDNR’s 

June 10, 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. 

IV. Proposed Action 

We are proposing to disapprove the 

MoDNR’s June 10, 2019 SIP submission 

pertaining to interstate transport of air 

pollution which will significantly 

contribute to nonattainment or interfere 

with maintenance of the 2015 8-hour 

ozone NAAQS in other states. Under 

CAA section 110(c)(1), disapproval 

would establish a 2-year deadline for 

the EPA to promulgate a FIP for 

Missouri 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 the EPA approves a SIP 

that meets these requirements. 

Disapproval does not start a mandatory 

sanctions clock for Missouri. 

V. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This action is not a significant 

regulatory action and was therefore not 

submitted to the Office of Management 

and Budget for review. 

B. Paperwork Reduction Act (PRA) 

This proposed action does not impose 

an information collection burden under 

the PRA because it does not contain any 

information collection activities. 

C. Regulatory Flexibility Act (RFA) 

I certify that this action will not have 

a significant economic impact on a 

substantial number of small entities 

under the RFA. This action merely 

proposes to disapprove a SIP 

submission as not meeting the CAA. 

D. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain any 

unfunded mandate as described in 

UMRA, 2 U.S.C. 1531–1538, and does 


lotter on DSK11XQN23PROD with PROPOSALS1
Federal Register / Vol. 87, No. 35 / Tuesday, February 22, 2022 / Proposed Rules 9545 

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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