Changeflow GovPing Legislation EPA Proposes Illinois Regional Haze Plan Approval

Priority review Rule Added Draft

EPA Proposes Illinois Regional Haze Plan Approval

EPA Rules & Proposed Rules

Published February 27th, 2026

Detected February 27th, 2026

Summary

The Environmental Protection Agency (EPA) has proposed approving Illinois's regional haze plan for the second implementation period. This action addresses the interstate transport of air pollution related to the 2012 PM2.5 and 2015 Ozone National Ambient Air Quality Standards. The public comment period for this proposed rule closes on March 30, 2026.

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What changed

The Environmental Protection Agency (EPA) has issued a proposed rule concerning the approval of Illinois's regional haze plan for the second implementation period. This proposal specifically addresses the interstate transport of air pollution, as it relates to the 2012 PM2.5 and 2015 Ozone National Ambient Air Quality Standards (NAAQS). The EPA is seeking public comment on this proposed approval, which is crucial for states to meet their obligations under the Clean Air Act regarding regional haze.

Regulated entities, particularly those in Illinois and potentially affected by interstate air pollution transport, should review the proposed plan and submit comments by the deadline of March 30, 2026. Failure to comply with regional haze requirements can lead to federal implementation plans and potential sanctions. This proposed rule is part of the ongoing efforts to improve air quality and visibility across the United States.

What to do next

Review the proposed Illinois regional haze plan for the second implementation period.
Submit public comments to the EPA by March 30, 2026.
Assess potential impacts on operations related to interstate air pollution transport.

Source document (simplified)

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Proposed Rule

Air Plan Approvals; Illinois; Regional Haze Plan for the Second Implementation Period; Interstate Transport of Air Pollution for the 2012 PM2.5 and 2015 Ozone NAAQS

A Proposed Rule by the Environmental Protection Agency on 02/27/2026

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1. | | Agency | Docket | Docket ID |
| --- | --- | --- | --- |
| Select | EPA | Illinois 2012 PM2-5 Infrastructure SIP | EPA-R05-OAR-2017-0583 |
| Select | EPA | Illinois 2015 Ozone Infrastructure SIP | EPA-R05-OAR-2019-0311 |
| Select | EPA | Illinois Regional Haze SIP Second Implementation Period | EPA-R05-OAR-2024-0261 |

Document Details Published Content - Document Details Agency Environmental Protection Agency Agency/Docket Numbers EPA-R05-OAR-2017-0583 EPA-R05-OAR-2019-0311 EPA-R05-OAR-2024-0261 FRL-13083-01-R5 CFR 40 CFR 52 Document Citation 91 FR 9779 Document Number 2026-03936 Document Type Proposed Rule Pages 9779-9793
(15 pages) Publication Date 02/27/2026 Published Content - Document Details
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Document Details Published Content - Document Details Agency Environmental Protection Agency Agency/Docket Numbers EPA-R05-OAR-2017-0583 EPA-R05-OAR-2019-0311 EPA-R05-OAR-2024-0261 FRL-13083-01-R5 CFR 40 CFR 52 Document Citation 91 FR 9779 Document Number 2026-03936 Document Type Proposed Rule Pages 9779-9793
(15 pages) Publication Date 02/27/2026 Published Content - Document Details
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| EPA-R05-OAR-2019-0311
(7 Documents) | | | |
| --- | | | |
| Date | | Action | Title |
| | 2026-02-27 | Proposed rule. | Air Plan Approvals; Illinois; Regional Haze Plan for the Second Implementation Period; Interstate Transport of Air Pollution for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2022-04-08 | Final rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2022-01-18 | Final rule. | Air Plan Approval; Illinois; Removal of Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2021-09-29 | Direct final rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2021-09-29 | Proposed rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2020-01-24 | Direct final rule. | Air Plan Approval; Illinois; Emissions Statement Rule Certification for the 2015 Ozone Standard |
| | 2020-01-24 | Proposed rule. | Air Plan Approval; Illinois; Emissions Statement Rule Certification for the 2015 Ozone Standard |

| EPA-R05-OAR-2017-0583
(7 Documents) | | | |
| --- | | | |
| Date | | Action | Title |
| | 2026-02-27 | Proposed rule. | Air Plan Approvals; Illinois; Regional Haze Plan for the Second Implementation Period; Interstate Transport of Air Pollution for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2022-04-08 | Final rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2022-01-18 | Final rule. | Air Plan Approval; Illinois; Removal of Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2021-09-29 | Direct final rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2021-09-29 | Proposed rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 and 2015 Ozone NAAQS |
| | 2019-06-20 | Final rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 NAAQS; Interstate Transport |
| | 2019-02-14 | Proposed rule. | Air Plan Approval; Illinois; Infrastructure SIP Requirements for the 2012 PM2.5 NAAQS; Interstate Transport |

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Environmental Protection Agency

40 CFR Part 52
EPA-R05-OAR-2017-0583; EPA-R05-OAR-2019-0311; EPA-R05-OAR-2024-0261; FRL-13083-01-R5 # AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing to approve the regional haze State Implementation Plan (SIP) revision submitted by the Illinois Environmental Protection Agency (Illinois EPA) on June 3, 2024, as satisfying applicable requirements under the Clean Air Act (CAA) and the EPA's Regional Haze Rule for the program's second implementation period. The EPA proposes to find that Illinois' regional haze SIP submission fulfills the requirement that States must periodically revise their long-term strategies for making reasonable progress towards the national goal of preventing any future, and remedying any existing, anthropogenic impairment of visibility in mandatory Class I Federal areas. The EPA is also proposing to approve portions of Illinois' September 29, 2017, and May 16, 2019, infrastructure SIP submissions for the 2012 fine particulate matter (PM 2.5) and 2015 ozone National Ambient Air Quality Standards (NAAQS), respectively. The EPA is proposing that Illinois' infrastructure submissions fulfill CAA requirements for a State's SIP to contain adequate provisions prohibiting emissions that will interfere with required visibility protection measures in any other State's SIP.

DATES:

Written comments must be received on or before March 30, 2026.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-R05-OAR-2024-0261 (Regional Haze) or EPA-R05-OAR-2019-0311 (infrastructure SIPs) at https://www.regulations.gov or via email to langman.michael@epa.gov. For comments submitted at Regulations.gov, follow the online instructions for submitting comments. 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 the EPA's docket at https://www.regulations.gov any information you consider to be confidential business information (CBI), Proprietary Business Information (PBI), or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (i.e., on the web, cloud, or other file sharing system). For additional submission methods, please contact the person identified in the FOR FURTHER INFORMATION CONTACT section. 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.

FOR FURTHER INFORMATION CONTACT:

Kelsey Foss, Air and Radiation Division (AR-18J), Environmental Protection Agency, Region 5, 77 West Jackson Boulevard, Chicago, Illinois 60604, (312) 886-6008, foss.kelsey@epa.gov. The EPA Region 5 office is open from 8:30 a.m. to 4:30 p.m., Monday through Friday.

SUPPLEMENTARY INFORMATION:

Throughout this document whenever “we,” “us,” or “our” is used, we mean the EPA.

This supplementary information section is arranged as follows:

I. What actions is the EPA proposing?

II. Background and Requirements for Regional Haze Plans

A. Regional Haze Background

B. Roles of Agencies in Addressing Regional Haze

III. Requirements for Regional Haze Plans for the Second Implementation Period

A. Long-Term Strategy for Regional Haze

B. Reasonable Progress Goals

C. Monitoring Strategy and Other State Implementation Plan Requirements

D. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals

E. Requirements for State and Federal Land Manager Coordination

IV. The EPA's Evaluation of Illinois' Regional Haze Submission for the Second Implementation Period

A. Background on Illinois' First Implementation Period SIP Submission

B. Illinois' Second Implementation Period SIP Submission and the EPA's Evaluation

C. Identification of Class I Areas

D. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and the Uniform Rate of Progress

E. Long-Term Strategy for Regional Haze

Selection of Sources for Analysis
Emission Measures Necessary To Make Reasonable Progress
Illinois' Long-Term Strategy
The EPA's Evaluation of Illinois' Compliance With 40 CFR 51.308(f)(2)(i)
Consultation With Federal Land Managers and States
Five Additional Factors

F. Reasonable Progress Goals

G. Monitoring Strategy and Other Implementation Plan Requirements

H. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals

I. Requirements for State and Federal Land Manager Coordination

V. Interstate Transport for the 2012 PM 2.5 and 2015 Ozone NAAQS Infrastructure SIPs—Visibility Component

A. Background on Infrastructure SIPs

B. The EPA's Evaluation of Illinois' Infrastructure SIP Submissions

VI. Proposed Actions

VII. Statutory and Executive Order Reviews

I. What Actions is the EPA Proposing?

On June 3, 2024, Illinois EPA submitted a revision to its SIP to address regional haze for the second implementation period. Illinois EPA submitted this SIP revision to satisfy the requirements of the CAA's regional haze program pursuant to CAA section 169A and 40 CFR 51.308. The EPA proposes to find that the Illinois regional haze SIP revision for the second implementation period meets the applicable statutory and regulatory requirements and thus proposes to approve the submission into Illinois' SIP.

On September 29, 2017, and May 16, 2019, Illinois EPA submitted SIP revisions addressing infrastructure requirements for the 2012 PM 2.5 NAAQS and the 2015 ozone NAAQS, respectively. The EPA proposes to approve both submissions as meeting CAA section 110(a)(2)(D)(i)(II), which requires a State's SIP to contain adequate provisions prohibiting emissions that will interfere with required visibility protection measures in any other State's SIP.

II. Background and Requirements for Regional Haze Plans

A detailed history and background of the regional haze program is provided in multiple prior EPA proposal actions. [1 ] For additional background on the 2017 Regional Haze Rule (RHR) revisions, please refer to Section III. Overview of Visibility Protection Statutory Authority, Regulation, and Implementation of “Protection of Visibility: Amendments to Requirements for State Plans” of the ( printed page 9780) 2017 RHR. [2 ] The following is an abbreviated history and background of the regional haze program and 2017 RHR as it applies to the current action.

A. Regional Haze Background

In the 1977 CAA Amendments, Congress created a program for protecting visibility in the nation's mandatory Class I Federal areas, which include certain national parks and wilderness areas. [3 ] CAA 169A. The CAA establishes as a national goal the “prevention of any future, and the remedying of any existing, impairment of visibility in mandatory class I Federal areas which impairment results from manmade air pollution.” CAA 169A(a)(1). Regional haze is visibility impairment that is produced by a multitude of anthropogenic sources and activities which are located across a broad geographic area and that emit pollutants that impair visibility. Visibility impairing pollutants include fine and coarse particulate matter (PM) (e.g., sulfates, nitrates, organic carbon, elemental carbon, and soil dust) and their precursors (e.g., sulfur dioxide (SO 2), nitrogen oxides (NO X), and, in some cases, volatile organic compounds (VOC) and ammonia (NH 3)). Fine particle precursors react in the atmosphere to form PM 2.5, which impairs visibility by scattering and absorbing light. Visibility impairment reduces the perception of clarity and color, as well as visible distance. [4 ]

To address regional haze visibility impairment, the 1999 RHR established an iterative planning process that requires both States in which Class I areas are located and States “the emissions from which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area to periodically submit SIP revisions to address such impairment. CAA 169A(b)(2); 5 see also 40 CFR 51.308(b), (f) (establishing submission dates for iterative regional haze SIP revisions); (64 FR 35714 at 35768, July 1, 1999).

On January 10, 2017, the EPA promulgated revisions to the RHR, (82 FR 3078, January 10, 2017), that apply for the second and subsequent implementation periods. The reasonable progress requirements as revised in the 2017 rulemaking (referred to here as the 2017 RHR Revisions) are codified at 40 CFR 51.308(f).

B. Roles of Agencies in Addressing Regional Haze

Because the air pollutants and pollution affecting visibility in Class I areas can be transported over long distances, successful implementation of the regional haze program requires long-term, regional coordination among multiple jurisdictions and agencies that have responsibility for Class I areas and the emissions that impact visibility in those areas. To address regional haze, States need to develop strategies in coordination with one another, considering the effect of emissions from one jurisdiction on the air quality in another. Five regional planning organizations (RPOs), which include representation from State and Tribal governments, the EPA, and Federal Land Managers (FLMs), were developed in the lead-up to the first implementation period to address regional haze. RPOs evaluate technical information to better understand how emissions from State and Tribal land impact Class I areas across the country, pursue the development of regional strategies to reduce emissions of particulate matter and other pollutants leading to regional haze, and help States meet the consultation requirements of the RHR.

The Lake Michigan Air Directors Consortium (LADCO) is an RPO that includes the States of Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin. LADCO's work is a collaborative effort of State governments, Tribal governments, and various Federal agencies established to initiate and coordinate activities associated with the management of regional haze, visibility, and other air quality issues in the Midwest. Along with the six LADCO States, participants in LADCO's Regional Haze Technical Workgroup include the EPA, the U.S. National Park Service (NPS), the U.S. Fish and Wildlife Service (FWS), the U.S. Forest Service (USFS), regional Tribal air programs, and local air agencies.

III. Requirements for Regional Haze Plans for the Second Implementation Period

Under the CAA and the EPA's regulations, all 50 States, the District of Columbia, and the U.S. Virgin Islands are required to submit regional haze SIPs satisfying the applicable requirements for the second implementation period of the regional haze program by July 31, 2021. Each State's SIP must contain a long-term strategy for making reasonable progress toward meeting the national goal of remedying any existing and preventing any future anthropogenic visibility impairment in Class I areas. CAA 169A(b)(2)(B). To this end, 40 CFR 51.308(f) lays out the process by which States determine what constitutes their long-term strategies, with the order of the requirements in 40 CFR 51.308(f)(1) through (3) generally mirroring the order of the steps in the reasonable progress analysis [6 ] and (f)(4) through (6) containing additional, related requirements. Broadly speaking, a State first must identify the Class I areas within the State and determine the Class I areas outside the State in which visibility may be affected by emissions from the State. These are the Class I areas that must be addressed in the State's long-term strategy. See 40 CFR 51.308(f), (f)(2). For each Class I area within its borders, a State must then calculate the baseline (five-year average period of 2000-2004), current, and natural visibility conditions (i.e., visibility conditions without anthropogenic visibility impairment) for that area, as well as the visibility improvement made to date and the “uniform rate of progress” (URP).

In developing the regulations required by CAA section 169A(b), the EPA established the concept of the URP for each Class I area. The URP is the linear rate of progress needed to attain natural visibility conditions, assuming a starting point of baseline visibility conditions in 2004 and ending with natural conditions in 2064. The URP is determined by drawing a straight line from the measured 2000-2004 baseline conditions (in deciviews) for the 20% most impaired days at each Class I area to the estimated natural conditions (in deciviews) for the 20% most impaired days in 2064. From this calculation, a URP value can be calculated for each ( printed page 9781) year between 2004 and 2064. This linear interpolation is used as a tracking metric to help States assess the amount of progress they are making towards the national visibility goal over time in each Class I area. See 40 CFR 51.308(f)(1). The EPA developed the URP to address the diverse concerns of Eastern and Western States and account for the varying levels of visibility impairment in Class I areas around the country while ensuring an equitable approach nationwide. For each Class I area, States must calculate the URP for the end of each implementation period (e.g., in 2028 for the second implementation period). [7 ] 40 CFR 51.308(f)(1)(vi)(A). States may also adjust the URP to account for impacts from anthropogenic sources outside the United States and/or impacts from certain wildland prescribed fires. 40 CFR 51.308(f)(1)(vi).

Each State having a Class I area and/or emissions that may affect visibility in a Class I area must then develop a long-term strategy that includes the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress in such areas. A reasonable progress determination is based on applying the four factors in CAA section 169A(g)(1) to sources of visibility impairing pollutants that the State has selected to assess for controls for the second implementation period. Additionally, as further explained below, the RHR at 40 CFR 51.308(f)(2)(iv) separately provides five “additional factors” [8 ] that States must consider in developing their long-term strategies. See 40 CFR 51.308(f)(2). A State evaluates potential emission reduction measures for those selected sources and determines which are necessary to make reasonable progress. Those measures are then incorporated into the State's long-term strategy. After a State has developed its long-term strategy, it then establishes RPGs for each Class I area within its borders by modeling the visibility impacts of all reasonable progress controls at the end of the second implementation period, i.e., in 2028, as well as the impacts of other requirements of the CAA. The RPGs include reasonable progress controls not only for sources in the State in which the Class I area is located, but also for sources in other States that contribute to visibility impairment in that area. The RPGs are then compared to the baseline visibility conditions and the URP to ensure that progress is being made towards the statutory goal of preventing any future and remedying any existing anthropogenic visibility impairment in Class I areas. 40 CFR 51.308(f)(2)-(3). For each Class I area, States must compare the RPG for the 20% most impaired days to the URP for the end of the implementation period. If the RPG is above the URP, then an additional “robust demonstration” requirement is triggered for each State that contributes to that Class I area. 40 CFR 51.308(f)(3)(ii). There are additional requirements in the rule, including FLM consultation, that apply to all visibility protection SIPs and SIP revisions. See e.g., 40 CFR 51.308(i).

A. Long-Term Strategy for Regional Haze

While States have discretion to choose any source selection methodology that is reasonable, whatever choices they make should be reasonably explained. To this end, 40 CFR 51.308(f)(2)(i) requires that a State's SIP submission include “a description of the criteria it used to determine which sources or groups of sources it evaluated.” The technical basis for source selection, which may include methods for quantifying potential visibility impacts such as emissions divided by distance metrics, trajectory analyses, residence time analyses, and/or photochemical modeling, must also be appropriately documented, as required by 40 CFR 51.308(f)(2)(iii).

Once a State has selected the set of sources, the next step is to determine the emissions reduction measures for those sources that are necessary to make reasonable progress for the second implementation period. [9 ] This is accomplished by considering the four factors—“the costs of compliance, the time necessary for compliance, and the energy and nonair quality environmental impacts of compliance, and the remaining useful life of any existing source subject to such requirements.” CAA 169A(g)(1). The EPA has explained that the four-factor analysis is an assessment of potential emission reduction measures (i.e., control options) for sources; “use of the terms ‘compliance’ and ‘subject to such requirements’ in section 169A(g)(1) strongly indicates that Congress intended the relevant determination to be the requirements with which sources would have to comply to satisfy the CAA's reasonable progress mandate.” 82 FR 3078 at 3091, January 10, 2017. Thus, for each source it has selected for four-factor analysis, [10 ] a State must consider a “meaningful set” of technically feasible control options for reducing emissions of visibility impairing pollutants. Id. at 3088.

EPA has also explained that, in addition to the four statutory factors, States have flexibility under the CAA and RHR to reasonably consider visibility benefits as an additional factor alongside the four statutory factors. [11 ] Ultimately, while States have discretion to reasonably weigh the factors and to determine what level of control is needed, 40 CFR 51.308(f)(2)(i) provides that a State “must include in its implementation plan a description of . . . how the four factors were taken into consideration in selecting the measure for inclusion in its long-term strategy.”

As explained above, 40 CFR 51.308(f)(2)(i) requires States to determine the emission reduction measures for sources that are necessary to make reasonable progress by considering the four factors. Pursuant to 40 CFR 51.308(f)(2), measures that are necessary to make reasonable progress towards the national visibility goal must be included in a State's long-term strategy and in its SIP. 12 If the outcome of a four-factor analysis is that an emissions reduction measure is necessary to make reasonable progress towards remedying existing or preventing future anthropogenic ( printed page 9782) visibility impairment, that measure must be included in the SIP.

The characterization of information on each of the factors is also subject to the documentation requirement in 40 CFR 51.308(f)(2)(iii). The reasonable progress analysis is a technically complex exercise, and also a flexible one that provides States with bounded discretion to design and implement approaches appropriate to their circumstances. Given this flexibility, 40 CFR 51.308(f)(2)(iii) plays an important function in requiring a State to document the technical basis for its decision making so that the public and the EPA can comprehend and evaluate the information and analysis the State relied upon to determine what emission reduction measures must be in place to make reasonable progress. The technical documentation must include the modeling, monitoring, cost, engineering, and emissions information on which the State relied to determine the measures necessary to make reasonable progress. Additionally, the RHR at 40 CFR 51.308(f)(2)(iv) separately provides five “additional factors” [13 ] that States must consider in developing their long-term strategies: (1) Emission reductions due to ongoing air pollution control programs, including measures to address reasonably attributable visibility impairment; (2) measures to reduce the impacts of construction activities; (3) source retirement and replacement schedules; (4) basic smoke management practices for prescribed fire used for agricultural and wildland vegetation management purposes and smoke management programs; and (5) the anticipated net effect on visibility due to projected changes in point, area, and mobile source emissions over the period addressed by the long-term strategy.

Because the air pollution that causes regional haze crosses State boundaries, 40 CFR 51.308(f)(2)(ii) requires a State to consult with other States that also have emissions that are reasonably anticipated to contribute to visibility impairment in a given Class I area. If a State, pursuant to consultation, agrees that certain measures (e.g., a certain emission limitation) are necessary to make reasonable progress at a Class I area, it must include those measures in its SIP. 40 CFR 51.308(f)(2)(ii)(A). Additionally, the RHR requires that States that contribute to visibility impairment at the same Class I area consider the emission reduction measures the other contributing States have identified as being necessary to make reasonable progress for their own sources. 40 CFR 51.308(f)(2)(ii)(B). If a State has been asked to consider or adopt certain emission reduction measures, but ultimately determines those measures are not necessary to make reasonable progress, that State must document in its SIP the actions taken to resolve the disagreement. 40 CFR 51.308(f)(2)(ii)(C). Under all circumstances, a State must document in its SIP submission all substantive consultations with other contributing States. 40 CFR 51.308(f)(2)(ii)(C).

B. Reasonable Progress Goals

Reasonable progress goals “measure the progress that is projected to be achieved by the control measures States have determined are necessary to make reasonable progress based on a four-factor analysis.” 82 FR 3078 at 3091, January 10, 2017.

For the second implementation period, the RPGs are set for 2028. Reasonable progress goals are not enforceable targets. 40 CFR 51.308(f)(3)(iii). While States are not legally obligated to achieve the visibility conditions described in their RPGs, 40 CFR 51.308(f)(3)(i) requires that “[t]he long-term strategy and the reasonable progress goals must provide for an improvement in visibility for the most impaired days since the baseline period and ensure no degradation in visibility for the clearest days since the baseline period.”

RPGs may also serve as a metric for assessing the amount of progress a State is making towards the national visibility goal. To support this approach, the RHR requires States with Class I areas to compare the 2028 RPG for the most impaired days to the corresponding point on the URP line (representing visibility conditions in 2028 if visibility were to improve at a linear rate from conditions in the baseline period of 2000-2004 to natural visibility conditions in 2064). If the most impaired days RPG in 2028 is above the URP (i.e., if visibility conditions are improving more slowly than the rate described by the URP), each State that contributes to visibility impairment in the Class I area must demonstrate, based on the four-factor analysis required under 40 CFR 51.308(f)(2)(i), that no additional emission reduction measures would be reasonable to include in its long-term strategy. 40 CFR 51.308(f)(3)(ii). To this end, 40 CFR 51.308(f)(3)(ii) requires that each State contributing to visibility impairment in a Class I area that is projected to improve more slowly than the URP provide “a robust demonstration, including documenting the criteria used to determine which sources or groups [of] sources were evaluated and how the four factors required by paragraph (f)(2)(i) were taken into consideration in selecting the measures for inclusion in its long-term strategy.”

C. Monitoring Strategy and Other State Implementation Plan Requirements

Section 51.308(f)(6) requires States to have certain strategies and elements in place for assessing and reporting on visibility. Individual requirements under this section apply either to States with Class I areas within their borders, States with no Class I areas but that are reasonably anticipated to cause or contribute to visibility impairment in any Class I area, or both. Compliance with the monitoring strategy requirement may be met through a State's participation in the Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring network, which is used to measure visibility impairment caused by air pollution at the 156 Class I areas covered by the visibility program. 40 CFR 51.308(f)(6), (f)(6)(i), (f)(6)(iv). All States' SIPs must provide for procedures by which monitoring data and other information are used to determine the contribution of emissions from within the State to regional haze visibility impairment in affected Class I areas, as well as a statewide inventory documenting such emissions. 40 CFR 51.308(f)(6)(ii), (iii), (v). All States' SIPs must also provide for any other elements, including reporting, recordkeeping, and other measures, that are necessary for States to assess and report on visibility. 40 CFR 51.308(f)(6)(vi).

D. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals

Section 51.308(f)(5) requires a State's regional haze SIP revision to address the requirements of paragraphs 40 CFR 51.308(g)(1) through (5) so that the plan revision due in 2021 will serve also as a progress report addressing the period since submission of the progress report for the first implementation period. The regional haze progress report requirement is designed to inform the public and the EPA about a State's implementation of its existing long-term strategy and whether such implementation is in fact resulting in the expected visibility improvement. See 81 FR 26942, 26950 (May 4, 2016), (82 FR 3078 at 3119, January 10, 2017). To this end, every State's SIP revision for the second implementation period is required to assess changes in visibility ( printed page 9783) conditions and describe the status of implementation of all measures included in the State's long-term strategy, including best available retrofit technology (BART) and reasonable progress emission reduction measures from the first implementation period, and the resulting emissions reductions. 40 CFR 51.308(g)(1) and (2).

E. Requirements for State and Federal Land Manager Coordination

CAA section 169A(d) requires that before a State holds a public hearing on a proposed regional haze SIP revision, it must consult with the appropriate FLM or FLMs; pursuant to that consultation, the State must include a summary of the FLMs' conclusions and recommendations in the notice to the public. Consistent with this statutory requirement, the RHR also requires that States “provide the [FLM] with an opportunity for consultation, in person and at a point early enough in the State's policy analyses of its long-term strategy emission reduction obligation so that information and recommendations provided by the [FLM] can meaningfully inform the State's decisions on the long-term strategy.” 40 CFR 51.308(i)(2). For the EPA to evaluate whether FLM consultation meeting the requirements of the RHR has occurred, the SIP submission should include documentation of the timing and content of such consultation. The SIP revision submitted to the EPA must also describe how the State addressed any comments provided by the FLMs. 40 CFR 51.308(i)(3). Finally, a SIP revision must provide procedures for continuing consultation between the State and FLMs regarding the State's visibility protection program, including development and review of SIP revisions, five-year progress reports, and the implementation of other programs having the potential to contribute to impairment of visibility in Class I areas. 40 CFR 51.308(i)(4).

IV. The EPA's Evaluation of Illinois' Regional Haze Submission for the Second Implementation Period

A. Background on Illinois' First Implementation Period SIP Submission

For the first implementation period covering the years 2007 through 2018, Illinois EPA submitted its regional haze SIP to the EPA on June 24, 2011, and the EPA approved it on May 29, 2012. See 77 FR 39943, July 6, 2012. The requirements for regional haze SIPs for the first implementation period are contained in 40 CFR 51.308(d) and (e).

Pursuant to 40 CFR 51.308(g), Illinois was also responsible for submitting a five-year progress report as a SIP revision for the first implementation period. On February 2, 2017, Illinois EPA submitted the progress report. The EPA approved this five-year progress report as a revision to the Illinois SIP at 40 CFR 52.720(e) on April 3, 2018. See 83 FR 15744, April 12, 2018.

B. Illinois' Second Implementation Period SIP Submission and the EPA's Evaluation

In accordance with section 169A of the CAA and the RHR at 40 CFR 51.308(f), Illinois EPA submitted a revision to the Illinois SIP on June 3, 2024, to address its regional haze obligations for the second implementation period, which runs through 2028. [14 ] In developing its 2024 SIP revision, Illinois EPA initiated an FLM consultation process and provided a public comment period for the second implementation period. The public comment period on the 2024 SIP revision ran from January 19, 2024, through March 21, 2024, and a public hearing was held on February 27, 2024. Illinois EPA received and responded to comments from FLMs and the public. Illinois EPA summarized and responded to the FLMs' comments in appendix H to the 2024 SIP submission. Illinois EPA included the public comments and its responses in attachments 3 and 4 to the 2024 SIP submission.

Prior to submitting its 2024 regional haze SIP revision and during the second implementation period, Illinois adopted amendments to its Multi-Pollutant Standards (MPS) Rule on August 22, 2019, [15 ] and submitted the amended MPS Rule to the EPA as a revision to its regional haze SIP on January 23, 2020. The EPA approved the revision on June 14, 2021, and revised Illinois' SIP at 40 CFR 52.720(c). 86 FR 13260, March 8, 2021, and 86 FR 33527, June 25, 2021. The MPS Rule established fleet-wide SO 2 and NO X emission limits for electric generating units (EGUs) and fulfilled the BART requirements of the first implementation period. The provisions of the MPS Rule are further described in section IV of Illinois' 2024 SIP submission and in section 2.1 of the EPA's November 12, 2025, Technical Support Document (TSD) for this proposed rulemaking, which is included in the docket.

The following sections describe Illinois' 2024 SIP submission, including Illinois EPA's assessment of progress made since the first implementation period in reducing emissions of visibility impairing pollutants and of the visibility improvement progress at nearby Class I areas. This notice of proposed rulemaking also contains the EPA's evaluation of Illinois' 2024 SIP submission against the requirements of the CAA and the RHR for the second implementation period of the regional haze program.

C. Identification of Class I Areas

Section 169A(b)(2) of the CAA requires each State in which any Class I area is located or “the emissions from which may reasonably be anticipated to cause or contribute to any impairment of visibility” in a Class I area to have a plan for making reasonable progress toward the national visibility goal. The RHR implements this statutory requirement at 40 CFR 51.308(f), which provides that each State's plan “must address regional haze in each mandatory Class I Federal area located within the State and in each mandatory Class I Federal area located outside the State that may be affected by emissions from within the State,” and (f)(2), which requires each State's plan to include a long-term strategy that addresses regional haze in such Class I areas.

The EPA concluded in the 1999 RHR that “all [s]tates contain sources whose emissions are reasonably anticipated to contribute to regional haze in a Class I area,” 64 FR 35714 at 35721, July 1, 1999, and this determination was not changed in the 2017 RHR. Critically, the statute and regulation both require that the cause-or-contribute assessment consider all emissions of visibility impairing pollutants from a State, as opposed to emissions of a particular pollutant or emissions from a certain set of sources.

Illinois has no Class I areas within its borders that are among the 156 mandatory Class I Federal areas where the EPA deemed visibility to be an important value. See 40 CFR part 81, subpart D. Thus, Illinois EPA only evaluated the State's impact on out-of-State mandatory Class I Federal areas covered under the RHR.

Illinois EPA is a member of LADCO and participated in the development of LADCO's strategy for making reasonable progress towards the national visibility goal in the Class I areas. To identify Class I areas where progress toward natural visibility conditions may be impacted by emissions from sources in ( printed page 9784) Illinois, Illinois EPA reviewed technical analyses conducted by LADCO. This included the technical analyses from the first implementation period compiled in 2007 by LADCO, known as the Midwest RPO at the time, to determine which Class I areas outside the State were affected by emission sources in Illinois. [16 ] These analyses included LADCO's back trajectory analysis and Comprehensive Air Quality Model with extensions and its Particulate Matter Source Apportionment Tool (CAMx-PSAT) as well as MANE-VU's contribution assessment, [17 ] Missouri-Arkansas' Contribution Assessment, VISTAS' Areas of Influence Analysis, [18 ] and WRAP's back trajectories and modeling. [19 ] Using LADCO's back trajectory analysis, LADCO initially assumed a State affected visibility impairment in a Class I area if it was projected to contribute two percent or more to the total light extinction. This threshold accounted for about 90-95 percent of the total light extinction at the Class I areas. Based on analyses conducted by other RPOs, LADCO gave deference to the criteria established by each RPO to identify additional Class I areas affected by LADCO States.

For the second regional haze implementation period, Illinois EPA reviewed later analyses by LADCO that also used CAMx-PSAT. [20 ] In its 2017 analyses, LADCO tagged States and regions as well as individual point sources and inventory source groups to apportion emissions to States and regions. LADCO assessed relative visibility impacts in 2028 by projecting representative emissions inventories and known emission controls from 2016. In 2017, a group of RPOs, States, and the EPA established 2016 as the base year for a national air quality modeling platform for future ozone, PM 2.5, and regional haze SIP development because that year had typical ozone and wildfire conditions. [21 ] LADCO relied upon the EPA's inventory estimates for 2016 and 2028 for most emission sectors as described in the EPA's September 19, 2019, “Availability of Modeling Data and Associated Technical Support Document for the EPA's Updated 2028 Visibility Air Quality Modeling,” (EPA's Updated 2028 Visibility Air Quality Modeling TSD). [22 ] For EGU emissions, LADCO used forecasts from the Eastern Regional Technical Advisory Committee (ERTAC) based on continuous emissions monitoring data from 2016 instead of the Integrated Planning Model used in the EPA's 2016 modeling platform. LADCO also incorporated State-reported changes to EGUs received through September 2020 to estimate 2028 EGU emissions.

Based on LADCO's 2007 and 2017 analyses, [23 ] Illinois EPA used the list of sources from the first implementation period to identify 16 Class I areas affected by emission sources in Illinois in the second implementation period. These Class I areas are: Boundary Waters Canoe Area Wilderness, Brigantine Wilderness Area, Caney Creek Wilderness Area, Great Gulf Wilderness Area, Great Smoky Mountains National Park, Hercules-Glades Wilderness Area, Isle Royale National Park, Lye Brook Wilderness, Acadia National Park, Mammoth Cave National Park, Mingo Wilderness Area, Moosehorn Wilderness Area, Seney Wilderness Area, Sipsey Wilderness Area, Upper Buffalo Wilderness Area, and Voyageurs National Park. [24 ] Illinois EPA characterized the list as conservative because emissions of visibility-impairing pollutants from sources in Illinois have declined since the first implementation period. 2028 visibility conditions at these Class I areas are projected by both LADCO and the EPA to be below the adjusted and unadjusted URP glidepaths provided in the EPA's Updated 2028 Visibility Air Quality Modeling TSD. These projections are depicted in Table 3.1 of Illinois' SIP submission and Table 8 of the EPA's November 12, 2025, TSD. Illinois EPA notes that the 2028 projections do not account for the 2019 revisions to the MPS, many emission reductions that have already taken place during the second implementation period, or all elements of Illinois' long-term strategy. As such, Illinois EPA anticipates greater improvements in visibility than those modeled in the projections by the EPA and LADCO.

D. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and the Uniform Rate of Progress

Section 51.308(f)(1) requires States to determine the following for “each mandatory Class I Federal area located within the State”: baseline visibility conditions for the most impaired and clearest days, natural visibility conditions for the most impaired and clearest days, progress to date for the most impaired and clearest days, the differences between current visibility conditions and natural visibility conditions, and the URP. This section also provides the option for States to propose adjustments to the URP line for a Class I area to account for visibility impacts from anthropogenic sources outside the United States and/or the impacts from wildland prescribed fires that were conducted for certain, specified objectives. 40 CFR 51.308(f)(1)(vi)(B).

Illinois has no mandatory Class I areas within its borders to which the requirements of the visibility protection program apply in 40 CFR part 81, subpart D. Therefore, 40 CFR 51.308(f)(1) and its requirements do not apply.

E. Long-Term Strategy for Regional Haze

Each State having a Class I area within its borders or emissions that may affect visibility in a Class I area must ( printed page 9785) develop a long-term strategy for making reasonable progress towards the national visibility goal. CAA 169A(b)(2)(B). After considering the four statutory factors, all measures that are determined to be necessary to make reasonable progress must be in the long-term strategy. In developing its long-term strategies, a State must also consider the five additional factors in 40 CFR 51.308(f)(2)(iv). As part of its reasonable progress determinations, the State must describe the criteria used to determine which sources or group of sources were evaluated (i.e., subjected to four-factor analysis) for the second implementation period and how the four factors were taken into consideration in selecting the emission reduction measures for inclusion in the long-term strategy. 40 CFR 51.308(f)(2)(iii).

1. Selection of Sources for Analysis

The provisions of 40 CFR 51.308(f)(2)(i) require States to describe the criteria used to determine which sources or groups of sources that State evaluated for potential emission reduction measures. States may rely on technical information developed by the RPOs of which they are members to select sources for four-factor analysis and to conduct that analysis, as well as to satisfy the documentation requirements under 40 CFR 51.308(f).

Illinois EPA described its source selection process in section IV of the 2024 SIP submission. In selecting sources to evaluate for potential control measure additions during the second implementation period, Illinois EPA considered SO 2, NO X, VOC, NH 3, and direct PM emissions but focused on NO X and SO 2 emissions following an analysis of IMPROVE data performed by LADCO. This analysis, described in LADCO's Technical Support Document “Modeling and Analysis for Demonstrating Reasonable Progress for the Regional Haze Rule 2018-2028 Planning Period,” (LADCO's 2021 TSD), [25 ] dated June 17, 2021, demonstrated that ammonium sulfate and ammonium nitrate are the largest components of haze during the most impaired days at the LADCO Class I areas. The LADCO Class I areas consist of Boundary Waters Canoe Area Wilderness and Voyageurs National Park in Minnesota and Isle Royale National Park and Seney Wilderness Area in Michigan. As precursors to ammonium sulfate and ammonium nitrate particulates, SO 2, and NO X, and NH 3 emissions contribute more to visibility impairment in the LADCO Class I Areas than direct PM 2.5 and VOC emissions. Illinois EPA determined that focusing on potential reductions in NO X and SO 2 emissions would be the most effective approach for the second implementation period. The EPA finds this approach to be reasonable, as noted in the “Guidance on Regional Haze State Implementation Plans for the Second Implementation Period,” EPA Office of Air Quality Planning and Standards, Research Triangle Park, August 20, 2019 (“2019 Regional Haze Guidance”) at page 12. [26 ] Illinois decided to focus specifically on NO X and SO 2 emissions from point sources based on information in the EPA's Updated 2028 Visibility Air Quality Modeling TSD, which provided a percentage breakdown of contributions to Class I areas by source sectors, such as point EGU point, non-EGU, nonpoint point, onroad, oil and gas, residential wood combustion, and anthropogenic dust. Table 4.1 of Illinois' 2024 SIP submission includes the percentage contributions to Class I areas affected by Illinois. The EGU and non-EGU point source sector emissions contribute the largest percentage, an average of 56 percent, of the visibility impairment in the Class I areas affected by Illinois. The EPA finds that Illinois EPA's decision to focus on NO X and SO 2 emissions from point sources is further supported by Tables 4-2 and 4-7 of LADCO's 2021 TSD, which show that emissions from point sources account for a large portion of both NO X and SO 2 emissions in Illinois, whereas NH 3, the third precursor to ammonium nitrate and ammonium sulfate, is mostly emitted from nonpoint sources.

Illinois EPA selected point sources for potential four-factor analyses based on LADCO's analyses of National Emissions Inventory (NEI) data. LADCO generated source lists based on total process-level emissions of NO X, SO 2, PM 2.5, and NH 3 (Q) divided by distance (d) to the center of the nearest Class I area, where Q/d was used as a surrogate quantitative metric of visibility impact in lieu of air quality modeling. The National Emissions Inventory Collaborative 2016 alpha inventory was selected in 2018 by the LADCO Regional Haze Technical Workgroup for the Q/d analysis as the best available inventory at that time. In support of using the 2016 data, Illinois EPA confirmed that there have been no emissions increases large enough to make use of the 2016 data inappropriate, especially since 2014-2020 NEI data demonstrates decreasing trends in NO X, PM 2.5, and SO 2 emissions. [27 ] For details on the data and methods used in the Q/d analysis, see LADCO's October 14, 2020, technical memorandum “Description of the Sources and Methods Used to Support Q/d Analysis for the 2nd Regional Haze Planning Period” [28 ] and section 5 of LADCO's 2021 TSD.

Illinois EPA designed its source selection methodology to capture a meaningful portion of Illinois' total contribution to visibility impairment in the Class I areas, including the largest sources in the State. Illinois EPA initially set a unit-level Q/d threshold of four to begin identifying point source emission units for potentially cost-effective control additions, where Q reflected LADCO's 2028 projections from the 2016 base year sum of NO X, SO 2, PM 2.5, and NH 3 emissions. To focus on sources with the greatest visibility impact, Illinois EPA then grouped those units by source and identified units with Q/d greater than four at facilities with Q/d greater than 10 for potential four-factor analyses. This resulted in a list of 30 units, accounting for 71.4 percent of all emissions of SO 2, NO X, NH 3, and PM 2.5 from units with Q/d greater than one in Illinois, including all the largest sources. Of these 30 units, 14 are no longer operating:

Electric Energy Inc.—Joppa, Units 1, 2, 3, 4, 5, and 6
Dynegy Midwest Generation LLC—Baldwin, Unit 13
Southern Illinois Power Cooperative—Marion, Unit 4
Illinois Power Resources Generating LLC—Edwards, Units 3 and 4
Illinois Power Generating Co.—Newton, Unit 13
Dynegy Midwest Generation LLC—Wood River, Unit 1
Will County Generating Station—Romeoville, Unit 16
Pacific Ethanol Pekin Inc., Unit 19 [29 ]
Illinois EPA then determined that the existing controls on the following seven units are effective to the extent that a full four-factor analysis would likely ( printed page 9786) result in a conclusion that no further controls are necessary.
Dynegy Midwest Generation LLC—Baldwin, Units 1 and 2 Illinois Power Generating Co.—Newton, Unit 3 Midwest Generation LLC—Powerton, Units 29 and 31 Kincaid Generation LLC, Units 8 and 9
Illinois EPA then selected the remaining nine units for four-factor analyses:
Prairie State Generating Station—Marissa, Units 4 and 5 Southern Illinois Power Cooperative—Marion, Unit 123 Rain CII Carbon LLC—Robinson, Units 1 and 2 Lafarge Midwest Inc.—Grand Chain, Units 47 and 66 [30 ]
- Archer Daniels Midland Co.—Decatur, Units 222 and 230 The demonstrations of existing effective controls and four-factor analyses are addressed under sections IV.E.2 and IV.E.4 of this preamble. Further details on Illinois EPA's source selection process, past retirements, demonstrations of existing effective controls, and four factor analyses are addressed in sections III, IV, V, and VI and appendix A of Illinois' 2024 SIP submission and sections 2 and 3 of the EPA's November 12, 2025, TSD.

2. Emission Measures Necessary To Make Reasonable Progress

The provisions of 40 CFR 51.308(f)(2)(i) require States to evaluate and determine the emission reduction measures that are necessary to make reasonable progress by applying the four statutory factors to sources in a control analysis. The emission reduction measures that are necessary to make reasonable progress must be included in the long-term strategy. 40 CFR 51.308(f)(2).

As mentioned above, Illinois EPA demonstrated that the seven units at Baldwin, Newton, Powerton, and Kincaid have existing effective control measures. Illinois EPA cited requirements contained in the MPS, the Combined Pollutant Standards (CPS), [31 ] and permits as well as 2016-2022 annual NO X and SO 2 emissions data to show that each unit has consistently implemented its existing measures and has achieved reasonably consistent annual emission rates that are not projected to increase in the future. For Baldwin, Newton, and Powerton, Illinois found that the existing measures under the MPS and CPS are necessary for reasonable progress for the second implementation period and documented that they form a part of the long-term strategy, are already federally enforceable and permanent, and are already included in the regulatory portion of Illinois' SIP at 40 CFR 52.720. For Kincaid, Illinois EPA referred to the existing BART measures that were previously included in the long-term strategy developed in the first implementation period. See 77 FR 3966, January 26, 2012. As such, Illinois EPA determined that additional control measures for the seven units at Baldwin, Newton, Powerton, and Kincaid are not necessary to make reasonable progress in the second implementation period. Illinois EPA's demonstrations of existing effective controls for these units are further described in section 3.3 of the EPA's November 12, 2025, TSD.

For the nine units at Prairie State, Marion, Rain CII Carbon, Lafarge Midwest, and Archer Daniels Midland, Illinois EPA provided a four-factor analysis as summarized in section V of Illinois' 2024 SIP submission and section 4 of the EPA's November 12, 2025, TSD. Appendix A to Illinois' submission describes the four-factor analyses in detail. Each analysis considered all four statutory factors and appropriately followed the methods in the EPA Air Pollution Control Cost Manual. [32 ] As presented in Table 1, Illinois EPA documented the range of cost effectiveness of potential new controls that were determined to be technically feasible.

| Facility | Unit | Control option | Cost effectiveness
(2020 dollars) |
| --- | --- | --- | --- |
| Prairie State Generating Station | Boilers 1 and 2 | Integrated Gasification Combined Cycle (IGCC) | $17,219 per ton of both SO 2 and NO X to remove 298.3 tons of NO X and 11,669 tons of SO 2 per year |
| Southern Illinois Power Cooperative | Boiler 123 | Fuel switch | $3,802 per ton of both SO 2 and NO X to remove 143.9 tons of NO X and 1,712 tons of SO 2 per year. |
| | | IGCC | $8,395.90 per ton of both SO 2 and NO X to remove 108.89 tons of NO X and 2017.69 tons of SO 2 per year. |
| Rain CII Carbon LLC | Kilns 1 and 2 | Selective Non-Catalytic Reduction (SNCR) | $3,395 per ton of NO X. |
| | | Selective Catalytic Reduction (SCR) | $7,701 per ton of NO X. |
| | | Semi-dry Flue Gas Desulfurization (FGD) | $9,570 per ton of SO 2. |
| | | Wet FGD | $29,106 per ton of SO 2. |
| Holcim US Inc | Kiln 1 | SNCR | $1,762 per ton of NO X for minimal or no NO X reductions. |
| | | Regenerative SCR | $6,042 per ton of NO X for minimal or no NO X reductions. |
| | | SCR upgrade | $659-$19,445 per ton of NO X to remove a maximum of 147 tons of NO X per year. |
| | | Dry FGD | $2,527-$97,556 per ton of SO 2. |
| | | Semi-dry FGD | $2,637-$51,744 per ton of SO 2. |
| | | Wet FGD | $1,648-$86,570 per ton of SO 2. |
| Archer Daniels Midland Co | Boilers 1-9 | SCR | $4,962-$7,252 per ton of NO X. |
| | | IGCC | $70,878 per ton of both NO X and SO 2. |
| | | Spray Dryer Absorber-FGD | $5,844-$8,010 per ton of SO 2; SO 2 reductions unlikely. |
| | | Wet FGD | $6,353-$8,930 per ton of SO 2; SO 2 reductions unlikely. |
For each unit, Illinois EPA determined that additional control measures are not necessary to make reasonable progress in the second implementation period and that pursuing additional emission reductions ( printed page 9787) through new emission control equipment or emissions limitations is not cost-effective. Illinois EPA determined this based on the units' existing controls, the cost of the alternative control measures, and the remaining useful life of the units. Illinois EPA also concluded that the existing emission control measures for each of these units are not necessary for reasonable progress for the second implementation period and do not need to be included in the regulatory portion of the SIP beyond where they are already included. Illinois EPA determined this based on the limits in the sources' air permits, historical data showing relatively consistent or declining NO X and SO 2 annual emissions, recent unit emission rates, and the 2028 projections of overall emissions showing that emissions are not expected to increase in the future.

3. Illinois' Long-Term Strategy

Each State's long-term strategy must include the enforceable emission limitations, compliance schedules, and other measures that are necessary to make reasonable progress. 40 CFR 51.308(f)(2). After considering information regarding existing effective controls, the four statutory factors in 40 CFR 51.308(f)(2)(i), and the five additional factors in 40 CFR 51.308(f)(2)(iv) in addition to other requirements in 40 CFR 51.308(f)(2)(ii) described below, Illinois EPA developed its long-term strategy for the second implementation period. Illinois EPA's long-term strategy is provided in section VI of Illinois' 2024 SIP submission and lists, at the State's discretion, measures beyond what the State deemed necessary for reasonable progress. Illinois EPA's long-term strategy lists State regulations such as the NO X Reasonably Available Control Technology (RACT) standards [33 ] as well as State regulations that are included in the regulatory part of Illinois' SIP at 40 CFR 52.720 for the MPS, [34 ] CPS, [35 ] and emission standards and limitations for Stationary Reciprocating Internal Combustion Engines (RICE) and Turbines. [36 ] Additionally, Illinois EPA's long-term strategy lists Federal measures for point sources including the Revised Cross-State Air Pollution Rule Update, [37 ] New Source Performance Standards (NSPS), [38 ] and National Emission Standards for Hazardous Air Pollutants (NESHAP), [39 ] as well as several Federal measures for area sources and on-road and non-road mobile sources. Of all the measures in the list, Illinois EPA only specified the State regulations for the MPS, CPS, and Stationary RICE and Turbines as necessary for reasonable progress in the second implementation period and reiterated that those measures are part of Illinois' SIP under 40 CFR 52.720, thus already federally enforceable and permanent. Illinois EPA did not identify any additional control requirements necessary for reasonable progress or any additional measures to be incorporated by reference into the regulatory portion of Illinois' SIP.

4. The EPA's Evaluation of Illinois' Compliance With 40 CFR 51.308(f)(2)(i)

The EPA proposes to find that Illinois has satisfied the requirements of 40 CFR 51.308(f)(2)(i) related to evaluating sources and determining the emission reduction measures that are necessary to make reasonable progress by considering the four statutory factors. The EPA is basing this proposed finding on the State's examination of its largest sources as described above. The State considered the four statutory factors, the historical emissions data, the emission reductions that have already taken place during the second implementation period, and the current control measures. As summarized above and further described in the EPA's November 12, 2025, TSD, Illinois' selection of sources and evaluation of control measures was reasonable and consistent with the requirements of 40 CFR 51.308(f)(2)(i).

In addition, as recently announced and applied in the approval of the West Virginia regional haze SIP submittal, [40 ] it is the EPA's policy that, where visibility conditions for a Class I area impacted by a State are below the URP and the State has considered the four statutory factors, the State will have presumptively demonstrated reasonable progress for the second implementation period for that Class I area. The EPA has the discretion and authority to change policy. In FCC v. Fox Television Stations, Inc., the U.S. Supreme Court plainly stated that an agency is free to change a prior policy and “need not demonstrate . . . that the reasons for the new policy are better than the reasons for the old one; it suffices that the new policy is permissible under the statute, that there are good reasons for it, and that the agency believes it to be better.” 566 U.S. 502, 515 (2009) (referencing Motor Vehicle Mfrs. Ass'n of United States, Inc. v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29 (1983)). See also Perez v. Mortgage Bankers Assn., 135 S. Ct. 1199 (2015). The EPA believes that its recently adopted policy aligns with the purpose of the statute and RHR, which is achieving “reasonable” progress, not maximal progress, toward Congress' natural visibility goal.

In the 2017 RHR Revisions, the EPA addressed the role of the URP as it relates to a State's development of its second implementation period SIP. 82 FR 3078 (January 10, 2017). Specifically, in response to comments suggesting that the URP should be considered a “safe harbor” that relieve States of any obligation to consider the four statutory factors, the EPA explained that the URP was not intended to be such a safe harbor. Id. at 3099. “Some commenters stated a desire for corresponding rule text dealing with situations where RPGs are equal to (“on”) or better than (“below”) the URP or glidepath. Several commenters stated that the URP or glidepath should be a `safe harbor,' opining that States should be permitted to analyze whether projected visibility conditions for the end of the implementation period will be on or below the glidepath based on on-the-books or on-the-way control measures, and that in such cases a four-factor analysis should not be required.” Id.

Other 2017 RHR comments indicated a similar approach, such as “a somewhat narrower entrance to a `safe harbor,' ” by suggesting that if current visibility conditions are already below the end-of-planning-period point on the URP line, a four-factor analysis should not be required.” Id. The EPA stated in its response that we did not agree with either of these recommendations. “The CAA requires that each SIP revision contain long-term strategies for making reasonable progress, and that in determining reasonable progress states must consider the four statutory factors. Treating the URP as a safe harbor would be inconsistent with the statutory requirement that states assess the potential to make further reasonable progress towards natural visibility goal in every implementation period.” Id.

However, so long as a State considers the four factors, the presumption that a Class I area below the URP is achieving reasonable progress is consistent with the CAA and RHR. Indeed, we believe this policy also recognizes the considerable improvements in visibility impairment that have been made by a wide variety of State and Federal programs in recent decades. In sum, Illinois EPA selected a number of ( printed page 9788) sources, evaluated emissions control measures, and considered the four statutory factors. In addition, as discussed in section 6 of the EPA's November 12, 2025, TSD, visibility conditions at all Class I areas to which Illinois contributes are below the URP. In light of these facts, this policy also supports the EPA's proposed finding that Illinois reasonably concluded that no additional measures are necessary to achieve reasonable progress during the second implementation period.

5. Consultation With Federal Land Managers and States

The consultation requirements of 40 CFR 51.308(f)(2)(ii) provide that States must consult with other States that are reasonably anticipated to contribute to visibility impairment in a Class I area to develop coordinated emission management strategies containing the emission reductions measures that are necessary to make reasonable progress. Section 51.308(f)(2)(ii)(A) and (B) require States to consider the emission reduction measures identified by other States as necessary for reasonable progress and to include agreed upon measures in their SIPs, respectively. Section 51.308(f)(2)(ii)(C) speaks to what happens if States cannot agree on what measures are necessary to make reasonable progress. States may also satisfy the requirement of 40 CFR 51.308(f)(2)(ii) to engage in interstate consultation with other States that have emissions that are reasonably anticipated to contribute to visibility impairment in a given Class I area under the auspices of intra- and inter-RPO engagement.

Although Illinois has no mandatory Class I Federal areas within its borders, emissions from sources within Illinois influence visibility at mandatory Class I Federal areas. Through intra- and inter-RPO engagement, Illinois EPA consulted with other States to develop a coordinated emission management approach to its regional haze SIP and to address Illinois' impact on nearby Class I areas. Consultation within LADCO and between LADCO and neighboring RPOs, including CenSARA [41 ] and VISTAS, [42 ] developed the technical information needed for such coordinated strategies. Inter-RPO cooperation is evident in LADCO's 2021 TSD and accompanying electronic docket, [43 ] which include area of influence modeling contributed by CenSARA and analyses for all Class I areas performed by LADCO.

Illinois EPA also received and responded to requests from MANE-VU, [44 ] Arkansas, [45 ] and Missouri [46 ] regarding regional haze. MANE-VU requested that Illinois ensure emission controls be operated year-round on certain EGUs and that Illinois pursue an ultra-low sulfur fuel oil standard. Illinois EPA replied that it already requires consistent NO X and SO 2 controls as well as an ultra-low sulfur fuel oil standard. In response to MANE-VU's request regarding the pursuit of energy initiatives, Illinois EPA noted Illinois' priorities on energy efficiency and other clean energy technologies. Arkansas requested that Illinois perform a four-factor analysis of Prairie State Generating Station because of its anticipated impact on visibility in the Upper Buffalo Wilderness Area. Illinois EPA replied that it would perform a four-factor analysis on this source. Missouri requested that Illinois consider performing four-factor analyses on Electric Energy Inc.—Joppa, Prairie State Generating Station, Southern Illinois Power Cooperative—Marion, and Dynegy Midwest Generation LLC—Baldwin. Illinois EPA addressed these sources in its 2024 SIP submission and cooperated with Missouri through LADCO and CenSARA. Illinois EPA did not receive any replies disagreeing with its responses. Section XIII of Illinois' SIP submission and section 5 of the EPA's November 12, 2025, TSD provide detailed summaries of Illinois' consultation with States, Tribes, and RPOs.

The EPA proposes to find that Illinois has satisfied the consultation requirements of 40 CFR 51.308(f)(2)(ii). Illinois has met the 40 CFR 51.308(f)(2)(ii)(A) and (B) requirements with its participation in the LADCO consultation process plus its individual communication with contributing States and RPOs. There were no disagreements with any other State, therefore 40 CFR 51.308(f)(2)(ii)(C) does not apply to Illinois.

The requirements of 40 CFR 51.308(f)(2)(iii) provide that a State must document the technical basis for its decision making to determine the emission reduction measures that are necessary to make reasonable progress. The documentation requirement of 40 CFR 51.308(f)(2)(iii) provides that States may meet their obligations to document the technical bases on which they are relying to determine the emission reductions measures that are necessary to make reasonable progress through an RPO, as long as the process has been “approved by all State participants.”

Illinois EPA adequately documented the technical basis that it relied on in determining the emission reduction measures that are necessary to make reasonable progress. By referencing and including LADCO's 2021 TSD as appendix B to its 2024 SIP submission, Illinois EPA also documented the Memorandum of Agreements between the Region 5 States and LADCO as well as the agreement from the States to use the analysis process provided by LADCO for regional haze efforts.

In addition to including LADCO's 2021 TSD as appendix B to its 2024 SIP submission, Illinois EPA described the technical analyses performed by LADCO and the EPA that the State relied upon for modeling visibility impacts of Illinois sources on Class I areas and projecting 2028 visibility conditions.

The cost and engineering analyses performed by Illinois EPA to address the four statutory factors were summarized in section V of the State's SIP submission and described in detail in appendix A to the submission.

Throughout its 2024 SIP submission, Illinois provided 2016 emissions data and other information used by LADCO to calculate Q/d values and project 2028 visibility conditions. Illinois EPA explained that because LADCO's Q/d analysis was performed in 2017, the 2016 emissions data used for the analysis was the best and most recent data available at the time. Also, as mentioned above, Illinois EPA reasoned that there have been no emissions increases large enough to make use of ( printed page 9789) the 2016 data inappropriate. Illinois EPA also provided Clean Air Markets Program Data (CAMPD) [47 ] from 2018 to 2022 that it had considered as well as the 2014, 2017, and 2020 NEI that it had submitted to the EPA to comply with the triennial reporting requirements of 40 CFR 51 subpart A.

As documented in Illinois' 2024 SIP submission, LADCO's analyses included the collection and analysis of ambient monitoring data, including the IMPROVE monitoring data. In section XII of its 2024 SIP submission, Illinois EPA described its monitoring network, which it uses to measure the ambient concentrations of pollutants including those that contribute to visibility degradation. Illinois also included its annual 2023 Ambient Air Monitoring Network Plan as appendix E to its 2024 SIP submission and committed to maintaining its monitoring network in section I of its 2024 SIP submission.

The EPA proposes to find that Illinois' documentation of the technical basis of the long-term strategy, including the modeling, monitoring, engineering, cost, and emissions information discussed above, satisfies the requirements of 40 CFR 51.308(f)(2)(iii).

The provisions of 51.308(f)(2)(iii) require that the emissions information considered to determine the measures that are necessary to make reasonable progress include information on emissions for the most recent year for which the State has submitted triennial emissions data to the EPA (or a more recent year), with a 12-month exemption period for newly submitted data. The most recent triennial NEI at the time of Illinois' SIP submission was 2020. Illinois EPA's regional haze SIP revision for the second implementation period included NEI data for 2014, 2017, and 2020. For its four-factor analyses and demonstrations of existing effective controls, Illinois EPA used 2015 to 2022 emissions data where applicable, including 2018—2022 data from CAMPD and 2028 projections from LADCO and ERTAC. Based on Illinois EPA's consideration and analysis of the emissions information to determine measures necessary for reasonable progress, including the most recent NEI available at the time and emissions data from other sources and years, the EPA proposes to find that Illinois has satisfied the emissions information requirement in 40 CFR 51.308(f)(2)(iii).

6. Five Additional Factors

In addition to the four statutory factors, section 169A(b)(2)(B) of the CAA requires the EPA to ensure that each SIP contains a long-term (ten to fifteen year) strategy for making reasonable progress toward meeting the national goal of addressing impairment of visibility in mandatory Class I Federal areas from manmade air pollution. Accordingly, the EPA established five additional factors listed in 40 CFR 51.308(f)(2)(iv) that States must consider in developing their long-term strategies. In section VIII of Illinois' 2024 SIP submission, Illinois EPA explained how it had addressed this requirement. For the reasons discussed below, the EPA proposes to find that Illinois adequately considered the five additional factors in developing its 2024 SIP submission.

As required by 40 CFR 51.308(f)(2)(iv)(A), Illinois considered emission reductions due to ongoing air pollution control programs. These include State and Federal regulations reducing emissions from point sources, on-road and non-road mobile sources, and area sources. Illinois EPA listed over 30 standards and programs that have been—and are expected to continue—limiting haze-forming emissions in Illinois.

Pursuant to 40 CFR 51.308(f)(2)(iv)(B), Illinois EPA considered measures to mitigate the impacts of construction activities on visibility in Class I areas. Illinois EPA noted that construction activities in Illinois are unlikely to contribute significantly to visibility impairment at Class I areas due to their distance from the State. Illinois EPA also explained that in addition to Federal non-road standards for construction vehicles and equipment, construction projects in Illinois are often subject to contract restrictions, including idling restrictions for construction vehicles and equipment; the EPA-approved controls for non-road diesel equipment; use of newer, cleaner, and more fuel-efficient engines for equipment; and optimizing earthwork and excavation to minimize haul trips. Illinois EPA noted that the State also requires the use of ultra-low sulfur diesel fuel, [48 ] which also mitigates the environmental impacts of construction because construction equipment generally uses diesel fuel. Finally, Illinois EPA committed to continue working with other State and Federal agencies to ensure that environmental impacts are given due consideration in construction project contracting.

As required by 40 CFR 51.308(f)(2)(iv)(C), Illinois EPA considered source retirement and replacement schedules in developing its long-term strategy.

In accordance with 40 CFR 51.308(f)(2)(iv)(D), Illinois EPA considered basic smoke management practices for prescribed fire used for agricultural and wildland vegetation management purposes and chose to prepare a statewide voluntary smoke management plan in cooperation with State land managers. The Illinois Smoke Management Plan is included as appendix F to Illinois' 2024 SIP submission and provides strategies for minimizing smoke during prescribed burns, best management practices for burns, and guidance on when to burn based on the Air Quality Index.

As required by 40 CFR 51.308(f)(2)(iv)(E), Illinois EPA considered the anticipated net effect on visibility due to projected changes in point, area, and mobile source emissions over the period addressed by its long-term strategy. This consideration led Illinois to choose to focus on point sources for the second implementation period but to also include measures controlling mobile and area source emissions in its long-term strategy. Illinois included tables in its submission showing 2016 emissions of NO X, PM 2.5, SO 2, and VOC from point, area, and mobile sources compared to projected 2028 emissions of the same pollutants by the same source categories.

After considering information regarding existing effective controls, the four statutory factors in 40 CFR 51.308(f)(2)(i), the five additional factors in 40 CFR 51.308(f)(2)(iv), and other requirements described above, the EPA proposes to find that Illinois has submitted a regional haze plan that meets the requirements of 40 CFR 51.308(f)(2) related to development of a long-term strategy. Thus, the EPA proposes to find that Illinois has satisfied the applicable requirements for making progress towards natural visibility conditions in Class I areas that may be affected by emissions from the State.

F. Reasonable Progress Goals

Section 51.308(f)(3) contains the requirements pertaining to RPGs for each Class I area. Section 51.308(f)(3)(i) requires a State in which a Class I area is located to establish RPGs—one each for the most impaired and clearest days—reflecting the visibility conditions that will be achieved at the ( printed page 9790) end of the implementation period as a result of the emission limitations, compliance schedules and other measures required under paragraph (f)(2) to be in States' long-term strategies, as well as implementation of other CAA requirements. The long-term strategies as reflected by the RPGs must provide for an improvement in visibility on the most impaired days relative to the baseline period and ensure no degradation on the clearest days relative to the baseline period. Section 51.308(f)(3)(ii) applies in circumstances in which a Class I area's RPG for the most impaired days represents a slower rate of visibility improvement than the uniform rate of progress calculated under 40 CFR 51.308(f)(1)(vi). Under 40 CFR 51.308(f)(3)(ii)(A), if the State in which a mandatory Class I area is located establishes an RPG for the most impaired days that provides for a slower rate of visibility improvement than the URP, the State must demonstrate that there are no additional emission reduction measures for anthropogenic sources or groups of sources in the State that would be reasonable to include in its long-term strategy. Section 51.308(f)(3)(ii)(B) requires that if a State contains sources that are reasonably anticipated to contribute to visibility impairment in a Class I area in another State, and the RPG for the most impaired days in that Class I area is above the URP, the upwind State must provide the same demonstration.

Because Illinois has no Class I areas within its borders to which the requirements of the visibility protection program apply in 40 CFR part 81, subpart D, Illinois is subject to 40 CFR 51.308(f)(3)(ii)(B), but not 40 CFR 51.308(f)(3)(i) or (f)(3)(ii)(A).

Under 40 CFR 51.308(f)(3)(ii)(B), a State that contains sources that are reasonably anticipated to contribute to visibility impairment in a Class I area in another State for which a demonstration by the other State is required under 40 CFR 51.308(f)(3)(ii)(B) must demonstrate that there are no additional emission reduction measures that would be reasonable to include in its long-term strategy. Table 3.1 of Illinois' 2024 SIP submission shows that at each of the Class I areas impacted by emissions from Illinois, the 2028 projected visibility impairment is not above the adjusted URP glidepaths for the 20 percent most impaired days. Because no Class I areas impacted by emissions from Illinois have RPGs above the 2028 URP, Illinois is not required to demonstrate that there are no additional emission reduction measures for anthropogenic sources or groups of sources that would be reasonable to include in their long-term strategies. Therefore, the EPA proposes that the demonstration requirement under 40 CFR 51.308(f)(3)(ii)(B) does not apply to Illinois.

The EPA proposes to determine that Illinois has satisfied the applicable requirements of 40 CFR 51.308(f)(3) relating to RPGs.

G. Monitoring Strategy and Other Implementation Plan Requirements

Section 51.308(f)(6) specifies that each comprehensive revision of a State's regional haze SIP must contain or provide for certain elements, including monitoring strategies, emissions inventories, and any reporting, recordkeeping and other measures needed to assess and report on visibility. A main requirement of this section is for States with Class I areas to submit monitoring strategies for measuring, characterizing, and reporting on visibility impairment. Compliance with this requirement may be met through participation in the IMPROVE network.

Section 51.308(f)(6)(i) requires SIPs to provide for the establishment of any additional monitoring sites or equipment needed to assess whether reasonable progress goals to address regional haze for all mandatory Class I Federal areas within the State are being achieved. Section 51.308(f)(6)(ii) requires SIPs to provide for procedures by which monitoring data and other information are used in determining the contribution of emissions from within the State to regional haze visibility impairment at mandatory Class I Federal areas both within and outside the State. All provisions under 40 CFR 51.308(f)(6) apply only to States containing mandatory Class I Federal areas listed in 40 CFR part 81, subpart D. As noted above, Illinois does not have any mandatory Class I Federal areas located within its borders to which the requirements of the visibility protection program apply in 40 CFR part 81, subpart D. Therefore, 40 CFR 51.308(f)(6)(i) and (ii) do not apply.

The provisions of 40 CFR 51.308(f)(6)(iii) require States with no Class I areas to include procedures by which monitoring data and other information are used in determining the contribution of emissions from within the State to regional haze visibility impairment at Class I areas in other States. States with Class I areas must establish a monitoring program and report data to the EPA that is representative of visibility at the Class I Federal areas. The IMPROVE network meets this requirement. Illinois EPA does not have any Class I areas or operate any monitoring sites under the Federal IMPROVE program. Therefore, the RHR does not require the approval of Illinois' monitoring network. However, Illinois EPA did include a description and a map of its monitoring network in its 2024 SIP revision and attached the Illinois Ambient Air Monitoring 2023 Network Plan as appendix E to the submission. Illinois EPA explained that the procedures by which monitoring data and other information are used to determine the contribution of Illinois emissions to visibility impairment at all affected Class I areas were established in conjunction with LADCO. Sections 7.0 and 8.0 of LADCO's TSD—included as appendix B to Illinois' 2024 SIP revision—describe the procedures.

Section 51.308(f)(6)(iv) requires the SIP to provide for the reporting of all visibility monitoring data to the Administrator at least annually for each Class I area in the State. As noted above, Illinois does not have any mandatory Class I Federal areas located within its borders to which the requirements of the visibility protection program apply in 40 CFR part 81, subpart D. Therefore, 40 CFR 51.308(f)(6)(iv) does not apply.

Section 51.308(f)(6)(v) requires SIPs to provide for a statewide inventory of emissions of pollutants that are reasonably anticipated to cause or contribute to visibility impairment, including emissions for the most recent year for which data are available and estimates of future projected emissions. It also requires a commitment to update the inventory periodically. Illinois' 2024 SIP submission provided statewide inventories of such emissions and future 2028 projected emissions in Tables 3.2, 3.3, 11.5, 11.6, and 11.7, including emissions information from the 2014, 2017, and 2020 NEI. Additionally, Illinois EPA provided CAMPD information for 2018 to 2022 and historical EGU emissions information from 1999 to 2020 in Figures 3.5 and 3.6. For future projected emissions, Illinois EPA relied on LADCO's analysis, which estimated 2028 projected emissions of SO 2 and NO X for specific facilities in the LADCO States based on 2016 emissions as well as ERTAC and State forecasts. These projected emissions were included in Illinois' 2024 SIP submission as well as in LADCO's TSD, which Illinois EPA included as appendix B to its 2024 SIP submission. In its 2024 SIP submission, Illinois EPA committed to continue updating its emissions inventory [49 ] and ( printed page 9791) to continue working with LADCO to project future emissions of relevant pollutants. The EPA proposes to find that Illinois has met the requirements of 40 CFR 51.308(f)(6).

H. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals

Section 51.308(f)(5) requires that periodic comprehensive revisions of States' regional haze plans also address the progress report requirements of 40 CFR 51.308(g)(1) through (5). The purpose of these requirements is to evaluate progress towards the applicable RPGs for each Class I area within the State and each Class I area outside the State that may be affected by emissions from within that State. Sections 51.308(g)(1) and (2) apply to all States and require a description of the status of implementation of all measures included in a State's first implementation period regional haze plan and a summary of the emission reductions achieved through implementation of those measures. Section 51.308(g)(3) applies only to States with Class I areas within their borders and requires such States to assess current visibility conditions, changes in visibility relative to baseline (2000-2004) visibility conditions, and changes in visibility conditions relative to the period addressed in the first implementation period progress report. Section 51.308(g)(4) applies to all States and requires an analysis tracking changes in emissions of pollutants contributing to visibility impairment from all sources and sectors since the period addressed by the first implementation period progress report. This provision further specifies the year or years through which the analysis must extend depending on the type of source and the platform through which its emission information is reported. Finally, 40 CFR 51.308(g)(5), which also applies to all States, requires an assessment of any significant changes in anthropogenic emissions within or outside the State have occurred since the period addressed by the first implementation period progress report, including whether such changes were anticipated and whether they have limited or impeded expected progress towards reducing emissions and improving visibility.

Prior to its 2024 SIP submission, Illinois submitted its first 5-year progress report to the EPA on February 2, 2017, and the EPA approved it on April 3, 2018. 83 FR 15744, April 12, 2018. Thus, the progress report elements included in section XI of Illinois' SIP revision for the second implementation period addressed 2017 through 2021. This is consistent with 40 CFR 51.308(f)(5), which requires States to address the elements in 40 CFR 51.308(g)(1) through (5) for the period since the most recent progress report.

As required by 40 CFR 51.308(g)(1), Illinois EPA described the implementation status of the measures relied on for reasonable progress in the first implementation period in section XI of its submission. These included NO X and SO 2 emission limits in source-specific permits for two EGUs—the City of Springfield's City Water, Light & Power facility in Dallman and Kincaid Generation, LLC; consent decrees mandating BART for two petroleum refineries—CITGO Petroleum Corporation and ExxonMobil Oil Corporation; and emission reductions at all EGUs subject to the MPS and CPS.

Pursuant to 40 CFR 51.308(g)(2), Illinois EPA summarized the emission reductions achieved through the implementation of these measures in Tables 4.4 through 4.7 and 11.1 through 11.4 of its submission. Illinois EPA also reproduced the list of on-the-books control strategies that had been included in its 2017 progress report and provided the status of these measures.

The provisions of 40 CFR 51.308(g)(3) require States to assess Reasonable Progress Goals, including current visibility conditions and changes, for any Class I areas within the State. Because Illinois has no Class I areas, the requirements of 40 CFR 51.308(g)(3) do not apply to Illinois.

Pursuant to 40 CFR 51.308(g)(4), Tables 11.5 to 11.7 of Illinois EPA's 2024 SIP submission tracked changes in emissions of CO, NH 3, NO X, PM 10, PM 2.5, SO 2, and VOCs from 2014 through 2020. Changes in NO X and SO 2 emissions from all Illinois EGUs from 1999 through 2020 were also provided in Figures 3.5 and 3.6 of the 2024 SIP submission and changes in NO X and SO 2 emissions from specific sources from 2018 through 2022 were provided in section VI of the 2024 SIP submission.

Addressing 40 CFR 51.308(g)(5), Illinois EPA did not identify any significant changes in anthropogenic emissions within the State that have occurred since its 2011 regional haze SIP submission that could limit or impede visibility progress. Illinois EPA reported that all projected emission reductions anticipated in the 2011 regional haze SIP submission and in the 2017 progress report have been realized.

The EPA proposes to find that Illinois EPA has met the requirements of 40 CFR 51.308(g)(1) through (5).

I. Requirements for State and Federal Land Manager Coordination

CAA section 169A(d) requires States to consult with FLMs before holding the public hearing on a proposed regional haze SIP, and to include a summary of the FLMs' conclusions and recommendations in the notice to the public. In addition, 40 CFR 51.308(i)(2) 's FLM consultation provision requires a State to provide FLMs with an opportunity for consultation that is early enough in the State's policy analyses of its emission reduction obligation so that information and recommendations provided by the FLMs' can meaningfully inform the State's decisions on its long-term strategy. If the consultation has taken place at least 120 days before a public hearing or public comment period, the opportunity for consultation will be deemed early enough. Regardless, the opportunity for consultation must be provided at least sixty days before a public hearing or public comment period at the State level. Section 51.308(i)(2) also provides two substantive topics on which FLMs must be provided an opportunity to discuss with States: assessment of visibility impairment in any Class I area and recommendations on the development and implementation of strategies to address visibility impairment. Section 51.308(i)(3) requires States, in developing their implementation plans, to include a description of how they addressed FLMs' comments.

Illinois engaged with FLMs at multiple points in the development process of its SIP revision, including NPS, USFS, FWS, and the U.S. Department of Interior—Bureau of Land Management. On March 9, 2020, NPS emailed Illinois a list of sources recommended for four-factor analysis. Illinois EPA shared a draft SIP revision with NPS and USFS on August 14, 2023, thus beginning the formal FLM consultation process over 120 days before posting the proposed SIP submission for public comment. On October 4, 2023, Illinois EPA attended a consultation call with NPS and USFS during which the FLMs summarized their conclusions and recommendations for the draft SIP revision. On October 13, 2023, Illinois received letters from NPS and USFS describing their recommendations in technical detail. As required by 40 CFR 51.308(i)(3) and noted in the EPA's November 12, 2025, TSD, Illinois summarized the FLMs' initial recommendations in section XIII of its SIP submission and included summaries of the FLMs' comments with a response to each, as well as the full ( printed page 9792) letters received from the FLMs, in appendix H of its submission.

Illinois published a public notice of its proposed SIP revision on Illinois EPA's website [50 ] on January 19, 2024, beginning a 30-day public comment period and stating that a public hearing would be held if requested. In accordance with 40 CFR 51.308(i)(2), Illinois began the public comment period at least 60 days after initiating the FLM consultation process and, as required by CAA section 169A(d), included summaries of the FLMs' recommendations in the public notice. On January 23, 2024, Illinois received requests for a hearing and an extension of the public comment period. On January 26, 2024, Illinois published a public notice of a virtual hearing to be held on February 27, 2024, and of a 30-day extension of the comment period. The hearing was held as planned on February 27, 2024. In total, Illinois received four written comments and one oral comment during the 60-day public comment period and concurrent hearing. Illinois included the public comments and Illinois' responses in attachments 3 and 4 to its submission, including a letter from NPS addressing Illinois' responses to NPS' initial recommendations for the SIP revision.

The provisions of 40 CFR 51.308(i)(4) require States to provide procedures for continuing consultation with FLMs on the implementation of visibility protection program requirements. As an active member of LADCO, Illinois continues to coordinate regularly with FLMs on the implementation of visibility protection plans and the planning of future work. In its 2024 SIP submission, Illinois committed to continue its fulfillment of all requirements of 40 CFR 51.308, including maintenance of adequate monitoring networks and production of emissions inventories, progress reports, and future SIP revisions. Given Illinois' actions recounted above, the EPA proposes to find that Illinois has satisfied the requirements of both 40 CFR 51.308(i) and 169A(d) to consult with the FLMs on its regional haze SIP for the second implementation period.

V. Interstate Transport for the 2012 PM

                2.5
                 and 2015 Ozone NAAQS Infrastructure SIPs—Visibility Component

A. Background on Infrastructure SIPs

Whenever the EPA promulgates a new or revised NAAQS, CAA section 110(a)(1) requires States to make SIP submissions to provide for the implementation, maintenance, and enforcement of the NAAQS. This particular type of SIP submission is commonly referred to as an “infrastructure SIP.” These submissions must meet the various requirements of CAA section 110(a)(2), as applicable. Due to ambiguity in some of the language of CAA section 110(a)(2), the EPA believes that it is appropriate to interpret these provisions in the specific context of acting on infrastructure SIP submissions. The EPA has previously provided comprehensive guidance on the application of these provisions through a guidance document for infrastructure SIP submissions (EPA's 2013 Guidance) and through regional actions on infrastructure submissions. [51 ] Unless otherwise noted below, we are following that existing approach in acting on this submission. In addition, in the context of acting on such infrastructure submissions, the EPA evaluates the submitting State's SIP for facial compliance with statutory and regulatory requirements, not for the State's implementation of its SIP. [52 ] The EPA has other authority to address any issues concerning a State's implementation of the rules, regulations, consent orders, etc. that comprise its SIP.

CAA section 110(a)(2)(D)(i)(II) prohibits emissions in one State from interfering with visibility protection measures in another State. On September 29, 2017, and May 16, 2019, Illinois submitted SIP revisions addressing infrastructure requirements for the 2012 PM 2.5 and 2015 ozone NAAQS, respectively.

This proposed rulemaking evaluates the element of Illinois EPA's SIP submissions for the 2012 PM 2.5 and 2015 ozone NAAQS addressing the fourth component (“Prong 4”) of CAA section 110(a)(2)(D)(i)—the requirement that a State's SIP contain adequate provisions prohibiting any source or other type of emissions activity within the State from emitting any air pollutant in amounts which will interfere with measures required to be included in the applicable SIP for any other State to protect visibility.

Under the applicable requirements for visibility protection of CAA section 110(a)(2)(D)(i)(II), States are subject to visibility and regional haze program requirements under part C of the CAA, which includes sections 169A and 169B. The EPA's 2013 Guidance states that these Prong 4 requirements can be satisfied by approved SIP provisions that the EPA has found to adequately address any contribution of that State's sources that impact the visibility program requirements in other States. [53 ] The EPA's 2013 Guidance lays out how a State's infrastructure SIP may satisfy Prong 4. In the second implementation period, confirmation that the State has a fully approved regional haze SIP that fully meets the requirements of 40 CFR 51.308 will satisfy the requirements of Prong 4. [54 ]

In the second implementation period, the EPA's Regional Haze regulations under 40 CFR 51.308(f) require that a State consider the emission reduction measures identified by other States as being necessary to make reasonable progress towards meeting the national visibility goal in Class I Federal areas. Specifically, the regulations also require a State to include in its Regional Haze SIP all measures agreed to during that process or measures that will provide equivalent visibility improvement. 40 CFR 51.308(f)(2)(ii). Thus, in meeting the requirements of 40 CFR 51.308(f), an approved regional haze SIP meeting the statutory and regulatory requirements, including 40 CFR 51.308(f)(2)(ii), will ensure that emissions from sources under an air agency's jurisdiction are not interfering with measures required to be included in other air agencies' plans to protect visibility and will, therefore, satisfy Prong 4. ( printed page 9793)

B. The EPA's Evaluation of Illinois' Infrastructure SIP Submissions

To address the requirements of CAA section 110(a)(2)(D)(i)(II), both Illinois EPA's September 29, 2017, infrastructure SIP submission for the 2012 PM 2.5 NAAQS and Illinois EPA's May 16, 2019, submission for the 2015 ozone NAAQS discuss the State's Prevention of Significant Deterioration program, nonattainment New Source Review program, and regional haze program. As discussed in the “Background on Illinois' First Implementation Period SIP Submission” section of this proposed rulemaking and noted in Illinois EPA's submissions, Illinois' regional haze SIP for the first implementation period was approved on July 6, 2012 (77 FR 39943), effective August 6, 2012.

In this proposed rulemaking, the EPA is proposing to approve Illinois' regional haze plan for the second implementation period. For the reasons stated above, by meeting the statutory and regulatory requirements of the regional haze program, including the interstate consultation requirements in 40 CFR 51.308(f)(2)(ii), Illinois' SIP adequately prohibits emissions from within the State that would interfere with visibility protection measures in any other State's SIP. Therefore, the EPA proposes that Illinois has met the applicable section 110(a)(2)(D)(i)(II) Prong 4 requirement relating to visibility protection for the 2012 PM 2.5 and 2015 ozone NAAQS.

VI. Proposed Actions

The EPA proposes to approve Illinois' SIP submission, dated June 3, 2024, as satisfying the regional haze requirements for the second implementation period contained in 40 CFR 51.308(f). The EPA also proposes to approve Illinois' SIP submissions, dated September 29, 2017, and May 16, 2019, as satisfying the interstate transport infrastructure requirements related to visibility protection contained in CAA section 110(a)(2)(D)(i)(II) for the 2012 PM 2.5 and 2015 ozone NAAQS.

VII. Statutory and Executive Order Reviews

Under the CAA, the Administrator is required to approve a SIP submission that complies with the provisions of the CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, the EPA's role is to approve State choices, provided that they meet the criteria of the CAA. Accordingly, this action merely approves State law as meeting Federal requirements and does not impose additional requirements beyond those imposed by State law. For that reason, this action:

Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);
Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review under Executive Order 12866;
Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.);
Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
Does not have federalism implications as specified in Executive Order 13132 (64 FR 43255, August 10, 1999);
Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;
Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and
Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the CAA. In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where the EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

List of Subjects in 40 CFR Part 52

Environmental protection
Air pollution control
Incorporation by reference
Nitrogen oxides
Ozone
Particulate matter
Sulfur oxides Dated: February 19, 2026.

Anne Vogel,

Regional Administrator, Region 5.

Footnotes

                     
                    See [90 FR 13516](https://www.federalregister.gov/citation/90-FR-13516) (March 24, 2025).

Back to Citation 2.

                     
                    See [82 FR 3078](https://www.federalregister.gov/citation/82-FR-3078) (January 10, 2017, located at *[https://www.federalregister.gov/documents/2017/01/10/2017-00268/protection-of-visibility-amendments-to-requirements-for-State-plans#h-16](https://www.federalregister.gov/documents/2017/01/10/2017-00268/protection-of-visibility-amendments-to-requirements-for-State-plans#h-16)).*

Back to Citation 3.

                     Areas statutorily designated as mandatory Class I Federal areas consist of national parks exceeding 6,000 acres, wilderness areas and national memorial parks exceeding 5,000 acres, and all international parks that were in existence on August 7, 1977. CAA 162(a). There are 156 mandatory Class I areas. The list of areas to which the requirements of the visibility protection program apply is in [40 CFR part 81, subpart D](https://www.ecfr.gov/current/title-40/part-81/subpart-D).

Back to Citation 4.

                     There are several ways to measure the amount of visibility impairment, *i.e.,* haze. One such measurement is the deciview, which is the principal metric used by the RHR. Under many circumstances, a change in one deciview will be perceived by the human eye to be the same on both clear and hazy days. The deciview is unitless. It is proportional to the logarithm of the atmospheric extinction of light, which is the perceived dimming of light due to its being scattered and absorbed as it passes through the atmosphere. Atmospheric light extinction (bext.

                    ) is a metric used for expressing visibility and is measured in inverse megameters (Mm −1). The formula for the deciview is 10 ln (bext.

                    )/10 Mm −1). [40 CFR 51.301](https://www.ecfr.gov/current/title-40/section-51.301).

Back to Citation 6.

                     The EPA explained in the 2017 RHR Revisions that we were adopting new regulatory language in [40 CFR 51.308(f)](https://www.ecfr.gov/current/title-40/section-51.308#p-51.308(f)) that, unlike the structure in 51.308(d), “tracked the actual planning sequence.” ([82 FR 3091](https://www.federalregister.gov/citation/82-FR-3091), January 10, 2017).

Back to Citation 7.

                     We note that RPGs are a regulatory construct that we developed to address the statutory mandate in CAA section 169B(e)(1), which required our regulations to include “criteria for measuring ‘reasonable progress’ toward the national goal.” Under [40 CFR 51.308(f)(3)(ii)](https://www.ecfr.gov/current/title-40/section-51.308#p-51.308(f)(3)(ii)), RPGs measure the progress that is projected to be achieved by the control measures a State has determined are necessary to make reasonable progress. Consistent with the 1999 RHR, the RPGs are unenforceable, though they create a benchmark that allows for analytical comparisons to the URP and mid-implementation-period course corrections if necessary. [82 FR 3091-3092](https://www.federalregister.gov/citation/82-FR-3091) (January 10, 2017).

Back to Citation 8.

                     The five “additional factors” for consideration in [40 CFR 51.308(f)(2)(iv)](https://www.ecfr.gov/current/title-40/section-51.308#p-51.308(f)(2)(iv)) are distinct from the four factors listed in CAA section 169A(g)(1) and [40 CFR 51.308(f)(2)(i)](https://www.ecfr.gov/current/title-40/section-51.308#p-51.308(f)(2)(i)) that states must consider and apply to sources in determining reasonable progress.

Back to Citation 9.

                     The CAA provides that, “[i]n determining reasonable progress there shall be taken into consideration” the four statutory factors. CAA 169A(g)(1). However, in addition to four-factor analyses for selected sources, groups of sources, or source categories, a State may also consider additional emission reduction measures for inclusion in its long-term strategy, *e.g.,* from other newly adopted, on-the-books, or on-the-way rules and measures for sources not selected for four-factor analysis for the second implementation period.

Back to Citation 10.

                     “Each source” or “particular source” is used here as shorthand. While a source-specific analysis is one way of applying the four factors, neither the statute nor the RHR requires States to evaluate individual sources. Rather, States have “the flexibility to conduct four-factor analyses for specific sources, groups of sources or even entire source categories, depending on state policy preferences and the specific circumstances of each state.” [82 FR 3078](https://www.federalregister.gov/citation/82-FR-3078) at 3088, January 10, 2017.

Back to Citation 11.

                     See, *e.g.,* Responses to Comments on Protection of Visibility: Amendments to Requirements for State Plans; Proposed Rule ([81 FR 26942](https://www.federalregister.gov/citation/81-FR-26942), May 4, 2016) (December 2016), Docket Number EPA-HQ-OAR-2015-0531, U.S. Environmental Protection Agency at 186.

Back to Citation 13.

                     The five “additional factors” for consideration in [40 CFR 51.308(f)(2)(iv)](https://www.ecfr.gov/current/title-40/section-51.308#p-51.308(f)(2)(iv)) are distinct from the four factors listed in CAA section 169A(g)(1) and [40 CFR 51.308(f)(2)(i)](https://www.ecfr.gov/current/title-40/section-51.308#p-51.308(f)(2)(i)) that States must consider and apply to sources in determining reasonable progress.

Back to Citation 14.

                     Since Illinois did not submit a complete SIP revision by the July 31, 2021, due date in the RHR, the EPA issued a finding of failure to submit on August 29, 2022. 
                    See [87 FR 52856](https://www.federalregister.gov/citation/87-FR-52856), August 30, 2022.

Back to Citation 15.

                    See 
                     Illinois Pollution Control Board, *In the Matter of: Amendments to 35 Ill. Adm. Code 225.233, Multi-Pollutant Standard (MPS),* R18-20, Adopted Rule, Final Order, August 22, 2019. *[https://pcb.illinois.gov/documents/dsweb/Get/Document-100916](https://pcb.illinois.gov/documents/dsweb/Get/Document-100916).*

Back to Citation 16.

                     The Midwest RPO's “Draft List of Class I Areas Located Within (or Impacted by) Midwest RPO States,” June 26, 2007 was included as attachment 1, appendix A of the Illinois' regional haze SIP for the first implementation period submitted to the EPA on June 24, 2011, and is contained in the docket for the rulemaking where the EPA approved the SIP on May 29, 2012: EPA-R05-OAR-2011-0598.

Back to Citation 17.

                     The Mid-Atlantic/Northeast Visibility Union (MANE-VU) is the RPO for the Northeastern and Mid-Atlantic States and Tribal governments, which include Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Penobscot Indian Nation, Rhode Island, St. Regis Mohawk Tribe, and Vermont.

Back to Citation 18.

                     Metro 4/SESARM/VISTAS refers to the Southeastern States Air Resources Managers, Inc. (SESARM) and the Visibility Improvement State and Tribal Association of the Southeast (VISTAS) as the RPO for Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennesse, Virginia, West Virginia, the Eastern Band of Cherokee Indians, and Knox County, Tennessee (representing the 17 Southeastern local air agencies).

Back to Citation 19.

                     The Western Regional Air Partnership (WRAP) is the RPO for Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon, Utah, and Wyoming.

Back to Citation 20.

                    See 
                     appendix B of Illinois 2024 SIP submission. Details of the analysis and source-apportioned visibility contributions at Class I areas for regional haze second implementation period are documented in LADCO's “Modeling and Analysis for Demonstrating Reasonable Progress for the Regional Haze Rule 2018-2028 Planning Period: Technical Support Document,” June 17, 2021.

Back to Citation 21.

                    See 
                     “Base Year Selection Workgroup Final Report,” produced by the Inventory Collaborative Base Year Selection Workgroup, April 5, 2017, available at *[https://drive.google.com/file/d/1o0e75dIliyjDZOmBDOPxIdMUhUTeph4Y/view](https://drive.google.com/file/d/1o0e75dIliyjDZOmBDOPxIdMUhUTeph4Y/view)* and included in the Docket EPA-R05-OAR-2024-0261 associated with this proposed rulemaking.

Back to Citation 22.

                     EPA, Office of Air Quality Planning and Standards, “Availability of Modeling Data and Associate Technical Support Document for EPA's Updated 2028 Visibility Air Quality Modeling,” September 19, 2019, available at *[https://www.epa.gov/sites/default/files/2019-10/documents/updated_2028_regional_haze_modeling-tsd-2019_0.pdf](https://www.epa.gov/sites/default/files/2019-10/documents/updated_2028_regional_haze_modeling-tsd-2019_0.pdf)* and included in the docket for this proposed rulemaking.

Back to Citation 23.

                    See 
                     appendix B of Illinois 2024 regional haze SIP submission for LADCO's technical support document and supporting materials.

Back to Citation 24.

                     A list of Class I areas impacted by Illinois and an accompanying map are found in section I of Illinois' 2024 SIP submission. Tables 3.1 and 4.1 of Illinois' 2024 SIP submission provide 2028 visibility projections for these areas based on modeling by LADCO and the EPA.

Back to Citation 25.

                     LADCO's 2021 TSD is contained in appendix B of Illinois' 2024 regional haze SIP submission.

Back to Citation 26.

                     The EPA's 2019 Regional Haze Guidance is available at *[https://www.epa.gov/visibility/guidance-regional-haze-state-implementation-plans-second-implementation-period](https://www.epa.gov/visibility/guidance-regional-haze-state-implementation-plans-second-implementation-period)* and is included in the docket for this proposed rulemaking.

Back to Citation 27.

                     See Tables 11.5 to 11.7 of Illinois' 2024 SIP submission.

Back to Citation 28.

                     LADCO's October 14, 2020, technical memorandum “Description of the Sources and Methods Used to Support Q/d Analysis for the 2nd Regional Haze Planning Period” contains a weblink to the spreadsheets and emissions data files used for the Q/d analysis and is publicly available in the docket for this proposed rulemaking and on LADCO's website at *[https://www.ladco.org/wp-content/uploads/Projects/Regional-Haze/Round2/LADCO_QoverD_Memo_16Oct2020.pdf](https://www.ladco.org/wp-content/uploads/Projects/Regional-Haze/Round2/LADCO_QoverD_Memo_16Oct2020.pdf).*

Back to Citation 29.

                     Pacific Ethanol Pekin Inc. is now Alto Pekin, LLC.

Back to Citation 30.

                     Lafarge Midwest Inc.—Grand Chain is now Holcim US, Inc.—Joppa Plant, Grand Chain.

Back to Citation 31.

                     The CPS are described in section IV of Illinois' 2024 regional haze SIP submission and in section 2.2 of the EPA's November 12, 2025, TSD.

Back to Citation 32.

                     
                    See 
                     the EPA's Air Pollution Control Cost Manual, available at *[https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/cost-reports-and-guidance-air-pollution](https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/cost-reports-and-guidance-air-pollution)* and included in the docket for this proposed rulemaking.

Back to Citation 33.

                     
                    See 
                     35 Illinois Administrative Code 217.

Back to Citation 34.

                     
                    See [86 FR 33527](https://www.federalregister.gov/citation/86-FR-33527), June 25, 2021.

Back to Citation 35.

                     
                    See [83 FR 8612](https://www.federalregister.gov/citation/83-FR-8612), February 28, 2018.

Back to Citation 36.

                     
                    See [74 FR 30466](https://www.federalregister.gov/citation/74-FR-30466), June 26, 2009.

Back to Citation 37.

                     
                    See [40 CFR 97, subpart GGGGG](https://www.ecfr.gov/current/title-40/part-97/subpart-GGGGG).

Back to Citation 38. 40 CFR 60.

Back to Citation 39. 40 CFR 63.

Back to Citation 40. 90 FR 16478, 16483, April 18, 2025, and 90 FR 29737, 29738-29740, July 7, 2025.

Back to Citation 41.

                     Central States Air Resource Agencies (CenSARA) is the RPO for the State and local governments of Arkansas, Iowa, Kansas, Louisiana, Missouri, Nebraska, Oklahoma, and Texas.

Back to Citation 42.

                     Visibility Improvement State and Tribal Association of the Southeast (VISTAS) is the RPO for the Southeastern State, Tribal, and local governments, which include Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, West Virginia, the Eastern Band of Cherokee Indians, and Knox County, Tennessee.

Back to Citation 43.

                     LADCO's electronic docket for its 2021 TSD is posted beneath the TSD documents at *<a href="https://www.ladco.org/reports/technical-support/ladco-regional-haze-tsd-second-implementation-period/">https://www.ladco.org/reports/technical-support/ladco-regional-haze-tsd-second-implementation-period/</a>.* The “2016-based 2028 glidepaths and PSAT tracer contributions” spreadsheet includes summaries of LADCO's 2016-based modeling for all Class I areas. A pdf version of this spreadsheet is included in the docket.

43.

                     See Figure 2-7 of LADCO's 2021 TSD.

Back to Citation 44.

                     The Mid-Atlantic/Northeast Visibility Union (MANE-VU) is the RPO for the Northeastern and Mid-Atlantic State and Tribal governments, which include Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Penobscot Indian Nation, Rhode Island, St. Regis Mohawk Tribe, and Vermont. MANE-VU's request and Illinois' response is addressed in section XIII and appendix D of Illinois' 2024 SIP submission.

Back to Citation 45.

                     Arkansas' request and Illinois' response is addressed in section XIII and appendix C of Illinois' 2024 SIP submission.

Back to Citation 46.

                     Missouri's request and Illinois' response are described in attachment 4 to Illinois' 2024 SIP submission.

Back to Citation 47.

                     The EPA's CAMPD information is publicly available at *<a href="https://campd.epa.gov/">https://campd.epa.gov/</a>.*

Back to Citation 48.

                     35 Illinois Administrative Code sections 214.122 and 214.305 limit the sulfur content of distillate fuel oil and residual fuel oil used by stationary sources. 35 Illinois Administrative Code 214 is available at *<a href="https://pcb.illinois.gov/documents/dsweb/Get/Document-11922/">https://pcb.illinois.gov/documents/dsweb/Get/Document-11922/</a>.*

Back to Citation 49.

                     The Air Emissions Reporting Requirements for State emissions inventories are codified in [40 CFR part 51, subpart A](https://www.ecfr.gov/current/title-40/part-51/subpart-A).

Back to Citation 50.

                     Illinois' proposed regional haze SIP revision submittal and all documents related to the public comment period and hearing were made publicly available at *[https://epa.illinois.gov/public-notices/general-notices.html](https://epa.illinois.gov/public-notices/general-notices.html).*

Back to Citation 51.

                     The EPA explains and elaborates on these ambiguities and its approach to address them in its September 13, 2013, “Guidance on Infrastructure State Implementation Plan (SIP) Elements under Clean Air Act sections 110(a)(1) and 110(a)(2)” (available at *[https://www3.epa.gov/airquality/urbanair/sipstatus/docs/Guidance_on_Infrastructure_SIP_Elements_Multipollutant_FINAL_Sept_2013.pdf](https://www3.epa.gov/airquality/urbanair/sipstatus/docs/Guidance_on_Infrastructure_SIP_Elements_Multipollutant_FINAL_Sept_2013.pdf)* and included in the docket for this proposed rulemaking), as well as in numerous agency actions, including the EPA's prior action on Michigan's, Illinois', Minnesota's, and Wisconsin's infrastructure SIPs to address the 2008 lead NAAQS ([79 FR 27241](https://www.federalregister.gov/citation/79-FR-27241) (May 13, 2014)).

Back to Citation 52.

                     See U.S. Court of Appeals for the Ninth Circuit decision in *Montana Environmental Information Center* v. *EPA,* No. 16-71933 (Aug. 30, 2018).

Back to Citation 53.

                     The EPA's 2013 Guidance at 32-33.

Back to Citation 54.

                     In the EPA's 2013 Guidance, we indicated that it may be appropriate to supplement the guidance regarding the relationship between regional haze SIPs and Prong 4 after second implementation period SIPs become due, which occurred on July 31, 2021. After a review of the EPA's 2013 Guidance and the second implementation period regional haze requirements, the EPA maintains the interpretation that a fully approved regional haze SIP satisfies Prong 4 requirements in the second implementation period.

Back to Citation [FR Doc. 2026-03936 Filed 2-26-26; 8:45 am]

BILLING CODE 6560-50-P

Published Document: 2026-03936 (91 FR 9779)

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EPA Proposes Illinois Regional Haze Plan Approval

Summary

What changed

What to do next

Source document (simplified)

Proposed Rule

Air Plan Approvals; Illinois; Regional Haze Plan for the Second Implementation Period; Interstate Transport of Air Pollution for the 2012 PM2.5 and 2015 Ozone NAAQS

Enhanced Content - Related Documents

Illinois 2012 PM2-5 Infrastructure SIP

Illinois 2015 Ozone Infrastructure SIP

Illinois Regional Haze SIP Second Implementation Period

- Sharing Enhanced Content - Sharing Shorter Document URL https://www.federalregister.gov/d/2026-03936 Email Email this document to a friend Enhanced Content - Sharing

Environmental Protection Agency

ACTION:

SUMMARY:

DATES:

ADDRESSES:

FOR FURTHER INFORMATION CONTACT:

SUPPLEMENTARY INFORMATION:

I. What Actions is the EPA Proposing?

II. Background and Requirements for Regional Haze Plans

A. Regional Haze Background

B. Roles of Agencies in Addressing Regional Haze

III. Requirements for Regional Haze Plans for the Second Implementation Period

A. Long-Term Strategy for Regional Haze

B. Reasonable Progress Goals

C. Monitoring Strategy and Other State Implementation Plan Requirements

D. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals

E. Requirements for State and Federal Land Manager Coordination

IV. The EPA's Evaluation of Illinois' Regional Haze Submission for the Second Implementation Period

A. Background on Illinois' First Implementation Period SIP Submission

B. Illinois' Second Implementation Period SIP Submission and the EPA's Evaluation

C. Identification of Class I Areas

D. Calculations of Baseline, Current, and Natural Visibility Conditions; Progress to Date; and the Uniform Rate of Progress

E. Long-Term Strategy for Regional Haze

1. Selection of Sources for Analysis

2. Emission Measures Necessary To Make Reasonable Progress

3. Illinois' Long-Term Strategy

4. The EPA's Evaluation of Illinois' Compliance With 40 CFR 51.308(f)(2)(i)

5. Consultation With Federal Land Managers and States

6. Five Additional Factors

F. Reasonable Progress Goals

G. Monitoring Strategy and Other Implementation Plan Requirements

H. Requirements for Periodic Reports Describing Progress Towards the Reasonable Progress Goals

I. Requirements for State and Federal Land Manager Coordination

V. Interstate Transport for the 2012 PM

A. Background on Infrastructure SIPs

B. The EPA's Evaluation of Illinois' Infrastructure SIP Submissions

VI. Proposed Actions

VII. Statutory and Executive Order Reviews

List of Subjects in 40 CFR Part 52

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