Regulatory Tracker

Regional Haze State Implementation Plans

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Why it Matters

Haze occurs when small particles of air pollution scatter and absorb sunlight, blurring scenic views and decreasing the distance that can be seen from overlooks. In response to this problem, Congress enacted Section 169A of the Clean Air Act (CAA) to protect visibility in national parks and wilderness areas. The Environmental Protection Agency (EPA) subsequently promulgated the Regional Haze Rule in 1999. The program directs states to implement pollution control plans to improve visibility and air quality at national parks, such as the Grand Canyon. Since the implementation of the regional haze program, the average visual range has increased from 90 to 120 miles in some western parks and from 50 to 70 miles in some eastern parks.

In addition to the benefits for visitors at national parks, the regional haze program delivers public health benefits. The primary pollutants that cause regional haze, including particulate matter, nitrogen oxides (NOx), sulfur dioxide (SO2), and volatile organic compounds (VOCs), are linked to serious health effects including premature death. Some of these pollutants also contribute to acid rain. Implementation of the Regional Haze Rule and associated regulations has produced sharp declines in the emissions of those pollutants, resulting in improved air quality as well as improved visibility in scenic areas. In fact, EPA estimates that during the first implementation period (2007-2018), there was a reduction in SO2 emissions of 500,000 tons per year and in NOx emissions of 300,000 tons per year.

For more information on EPA’s guidance for states developing regional haze plans, visit our post on the Regional Haze Rule

Overview and History of the Regional Haze SIPs

The first state plans were due in 2007. Plan revisions are required every decade, with the first full revision now due in 2021 (postponed from an original 2018 deadline). As part of the SIPs, states must calculate and work towards interim, short-term progress goals, with a long-term goal of returning targeted areas to their natural conditions by 2064.

The Clean Air Act and EPA regulations also mandate that certain older power plants adopt pollution abatement methods, known as “Best Available Retrofit Technology.” EPA allows this requirement to be met through a variety of methods: installing and operating specific technology, like scrubbers; requiring that sections of the facility periodically shut down to decrease overall annual emissions, known as “seasonal curtailment;” or integrating the power plants into the interstate emissions trading program, CSAPR.

If sections of the state’s SIP will not result in sufficient improvement to air visibility and quality, including if EPA determines that the pollution control technology is inadequate for specific facilities, EPA is expected to issue a FIP. EPA may also work with the state to revise the SIP. The FIP often addresses the insufficiency of the state’s interim progress goals, as well as specific technology controls for facilities. In practice, FIPs have been effective tools to compel states to take the action required under law even when they are reluctant to do so.

State-Specific History and Trump Era Regional Haze Actions


Dec. 5, 2012 EPA publishes a final rule that partially disapproves one section of Arizona’s SIP and promulgated a FIP to require certain NOx controls for the Cholla Power Plant, a coal-burning plant in Arizona.

Sep. 3, 2014 EPA publishes a final rule completing the 2012 FIP for certain disapproved sections of Arizona’s SIP. The FIP promulgates control technologies for five facilities in Arizona and addresses the short-term progress goals for two facilities in the state.

Oct. 13, 2014 Arizona files a petition for review of EPA’s FIP in the 9th Circuit Court of Appeals. In November, three of the facilities regulated by the FIP file separate petitions for review in the 9th Circuit. The four cases are consolidated as Arizona ex rel Henry Darwin v. USEPA, et al, Docket No. 14-73368.

Jan. 27, 2015 Industry files a motion to stay the final rule.

June 21, 2016 Oral argument is held in Arizona ex rel Henry Darwin v. EPA.


March 27, 2017 EPA publishes a final rule approving a source-specific SIP revision for the Cholla Power Plant in northeastern Arizona. The SIP requires that two units at the plant eventually stop burning coal but allows the plant to emit more NOx than would have been permitted under the previous FIP promulgated by the Obama administration.

April 3, 2017 The 9th Circuit upholds the legality of EPA’s FIP for Arizona as it relates to the emissions controls imposed on the three facilities that filed petitions for review in Arizona ex rel Henry Darwin v. EPA. The court also dismisses some claims brought by the state and industry.

Oct. 10, 2017 EPA issues a final rule approving Arizona’s SIP for the Coronado Generating Station. The rule allows Arizona to require alternative technology controls that will require temporary shutdown of the facility in order to meet the regional haze goals. This is different than using control technology that causes continuous lower pollution levels of NOx, which the Obama administration had proposed.

June 11, 2018 EPA approves Arizona’s SIP for Maricopa County.

July 11, 2019 EPA approves Arizona’s five-year status report and a determination by Arizona that the state’s existing regional haze plans are adequate and do not require revisions.  Arizona submitted the status report on November 12, 2015.


Sep. 27, 2016 EPA publishes a final rule that issued a FIP for Arkansas and includes pollution limits for NOx, SO2, and particulate matter for six facilities, as well as SO2 and NOx limits for an additional facility. The FIP also establishes short-term progress goals for reducing haze over Arkansas’ protected areas. The FIP gives power plants 18 months to comply with the rule.

Nov. 22, 2016 The state of Arkansas files a petition for review of the FIP in the 8th Circuit Court of Appeals. Industry and conservation groups join the suit later that month and file individual petitions for review. The court later consolidates the cases as State of Arkansas v. EPA, Docket No. 16-4270.


Feb. 7, 2017 Arkansas asks for a stay of the FIP. Industry files a motion for a stay on February 8, 2017.

March 7, 2017 EPA files an unopposed motion to hold the case in abeyance. The court grants this motion on March 8, 2017. The court has continued to hold the case in abeyance.

April 14, 2017 EPA agrees to reconsider certain aspects of the final rule. On April 25, 2017, EPA extends the 18-month compliance deadline for certain facilities by 90 days.

July 12, 2017 Arkansas proposes revisions to the SIP regarding NOx controls for power plants. The proposed SIP states that no additional controls are needed beyond the CSAPR interstate trading provisions.

July 13, 2017 EPA proposes a rule to approve these revisions. EPA also proposes a rule extending the compliance dates for additional facilities until January 27, 2020.

Dec. 15, 2017 Arkansas files a motion for a stay of the final rule. EPA does not oppose Arkansas’ motion, and industry supports it. Environmental groups oppose the stay.

Feb. 12, 2018 EPA publishes a final rule approving Arkansas’ July 12 SIP and rescinding the portions of the FIP requiring more stringent NOx controls for the affected power plants.

March 7, 2018 The court grants industry’s motion for a stay on the SO2 emission limits, allowing three facilities in Arkansas to delay reducing their emissions while the state finalizes its SIP revisions.

March 21, 2018 The conservation groups file a motion for reconsideration of the stay.

July 13, 2018 and September 13, 2018 The court denies the conservation groups’ motions to lift the abeyance. The court has not yet responded to the motion to reconsider the stay on the SO2 emission limits.

Nov. 30, 2018 EPA proposes to approve Arkansas’ final revisions to the 2008 Regional Haze SIP. Arkansas submitted the revisions to EPA on Aug. 8, 2018.

Sep. 27, 2019 EPA finalizes its approval of Arkansas’ SIP revisions, including revisions to the SO2 limits, and withdraws the corresponding, more-stringent FIP provisions.

Oct. 1, 2019 EPA approves Arkansas’ five-year status report and a determination by Arkansas that the state’s existing regional haze plans are adequate and do not require revisions. Arkansas originally submitted the status report on June 2, 2015.

Nov. 25, 2019 Sierra Club and the National parks Conservation Association file a petition for review of EPA’s Sept. 27 approval of Arkansas’ SIP revisions.

Dec. 18, 2019 The 8th Circuit grants a joint motion to hold in abeyance Sierra Club v. EPA, No. 19-3526. The case is paused pending the District Court’s entry of a settlement agreement between the Sierra Club and Entergy Arkansas that would resolve the issues in the case. That settlement agreement is part of a separate lawsuit – Sierra Club v. Entergy Arkansas, Case No. 4:18-cv-00854-KGB (E.D. Ark.).


Jan. 5, 2016 EPA partially disapproves Texas’ revised SIP and promulgates a FIP, which includes SO2 controls for eight coal-fired power plants. The controls are estimated to reduce SO2 emissions by 230,000 tons annually.

March 1, 2016 Texas and industry groups file petitions for review of EPA’s actions in the 5th Circuit Court of Appeals, State of Texas, et al v. EPA, Docket No. 16-60118.

March 3, 2016 Industry files a motion to stay the final rule. Texas files an additional motion to stay on March 17, 2016. The court grants the motion to stay the rule on July 15, 2016.

Dec. 2, 2016 EPA files a motion to remand the case to EPA for reconsideration following settlement discussions between the parties.

Jan. 4, 2017 EPA publishes a new proposed rule to impose SO2 limits on 14 power plants in Texas. The limits are expected to reduce emissions by approximately 194,000 tons annually. The FIP also allows Texas to meet its NOx requirements by participating in CSAPR.


Feb. 23, 2017 The 5th Circuit grants EPA’s motion to remand the case to the agency.

Oct. 17, 2017 EPA issues a final rule partially approving Texas’ SIP and issuing a FIP, allowing Texas to meet requirements for SO2 and NOx emissions through an intrastate trading system.

Dec. 15, 2017 coalition of conservation organizations files a petition for review of the final rule in the 5th Circuit, National Parks Conservation Association, et al v. EPA, Docket No. 17-60828. The groups also file a petition with EPA to reconsider the rule. Both petitions argue that the final rule published in October is unlawful because the intrastate trading system is unrelated to the proposed FIP that EPA published in January.

March 7, 2018 Following a joint motion by the conservation groups and EPA, the 5th Circuit stays the case pending EPA’s reconsideration of the final rule.

Aug. 27, 2018 EPA publishes a proposed rule affirming its actions in October 2017 to partially approve Texas’ SIP and to issue a FIP, enabling Texas to establish an intrastate trading program.

Nov. 14, 2019 EPA publishes a supplemental notice of proposed rulemaking to propose four revisions to the intrastate SO2 trading program finalized in Oct. 2017. The proposed modifications include adding an “assurance level” – an annual emissions limit that triggers a penalty for units that exceed the limit.

June 29, 2020 EPA issues a final rule approving Texas’ intrastate SO2 trading program. The final plan includes an “assurance level” – an annual emissions limit that triggers a penalty for units that exceed the limit. EPA sets the assurance level around 290,000 tons.


July 5, 2016 EPA partially approves Utah’s SIP and promulgates a FIP that would impose NOx emissions limits on two facilities in Utah.

Sep. 1, 2016 Utah files a petition for review in the 10th Circuit. Industry also files petitions for review in the 10th Circuit. The court later consolidates the three cases as State of Utah v. EPA, et al, Docket No. 16-09541.

Oct. 28, 2016 Utah and industry file separate motions to stay the rule. EPA opposes these motions on December 16, 2016.


Feb. 15, 2017 EPA files a motion to postpone deciding whether it will continue to oppose the motion for a stay. EPA files two motions in March and May further postponing this action.

July 18, 2017 EPA decides to reconsider the FIP and files a motion to abate the case in Utah.

Sep. 11, 2017 The court grants the motions for a stay and EPA’s motion to abate the case. The court requires that EPA provide status reports every 90 days.

Dec. 13, 2017 EPA files a status report stating that it is investigating updated technical analysis to revise the rule.

March 12, 2018 EPA files a status report stating that the updated air quality model simulations are expected to be completed by May. Following evaluation of the simulations, EPA will move forward with publishing a new proposed rule for Utah.

Sep. 10, 2018 EPA files a status report stating that the updated modeling and technical analyses are still being developed. Per the 10th Circuit’s order, the case remains on hold.

June 24, 2019 Utah’s Air Quality Board adopts revised regional haze sections of the state’s SIP.

Sep. 9, 2019 EPA’s status report states that Utah submitted the draft SIP amendments to EPA for approval and is finalizing additional revisions to the state’s regional haze SIP.

Jan. 22, 2020 EPA publishes a proposed rule to approve Utah’s SIP revision related to the Hunter and Huntington power plants. This rule would withdraw the FIP that EPA put into place in 2016. The SIP imposes less stringent NOx emissions controls on the two plants and relies on the shutdown of a different power plant to achieve the required reasonable progress towards visibility improvement.

Oct. 28, 2020 EPA finalizes its approval of Utah’s SIP and its withdrawal of the FIP.


Jan. 30, 2014 EPA publishes a final rule that partially approved Wyoming’s SIP and promulgated a FIP for Wyoming that establishes NOx controls for three facilities in the state.

March 28, 2014 Wyoming and conservation groups file opposing petitions for review of EPA’s actions in the 10th Circuit Court of Appeals.

March 31, 2014 Industry groups also petition the court for review. These four cases are later consolidated under Basin Electric Power v. EPA, et al, Docket No.14-09533.

June 11, 2014 The state of Wyoming and industry file separate motions to stay the final rule.

Sept. 9, 2014 The 10th Circuit grants the motions for a stay.


April 24, 2017 EPA, Wyoming, and the Basin Electric Power Cooperative reach a settlement regarding the Laramie River Generating Station.

April 28, 2017 EPA, industry, and Wyoming file a motion to abate proceedings on all four petitions. The court grants this motion on May 17, 2017.

June 2, 2017 The conservation groups file a motion to proceed separately with their case in Wyoming, as the settlement agreement only covers one facility and does not address many of the groups’ challenges to the final rule.

June 12, 2017 EPA opposes the conservation groups’ motion, arguing that the cases should not be severed, as the four petitions all challenge the same final rule.

June 19, 2017 The 10th Circuit denies the conservation groups’ motion and keeps the proceedings on hold for all four consolidated cases. The court continues this hold on November 9, 2017 and again on May 8, 2018, awaiting the final implementation of the settlement agreement. 

April 5, 2018 Wyoming submits a revised SIP to EPA for review. EPA has until October 5, 2018 to issue a proposed revision to the FIP.

May 20, 2019 EPA approves the Wyoming SIP revisions, submitted April 5, 2018, and revisions to the FIP for regional haze in Wyoming. The revisions modify the sulfur dioxide (SO2) emissions reporting requirements in the SIP for Laramie River Station power plant and the nitrogen oxides (NOx) and SO2 emission limits in the FIP.

Oct. 24, 2019 PacifiCorp files a petition for reconsideration of EPA’s 2014 FIP as it relates to the required pollution control technology for a specific coal-fired plant – Wyodak – based on updated cost estimates.


May 22, 2019 EPA proposes to fully approve Indiana’s SIP and SIP revisions. If finalized, this action will withdraw the FIP that EPA previously promulgated for Indiana.

Sep. 6, 2019 EPA finalizes its approval of Indiana’s SIP and its withdrawal of the FIP.


Sep. 12, 2017 EPA finalizes revisions to Montana’s FIP, which EPA promulgated in 2012 after the state did not submit a regional haze SIP. EPA acknowledges that these revisions do not address portions of the FIP that the 9th circuit vacated in 2015.

Oct. 4, 2019 EPA approves Montana’s five-year status report and a determination by Montana that the existing FIP is adequate and does not require revisions. Montana originally submitted the status report on November 7, 2017.

Cross-State Air Pollution Rule Updates

For other states, EPA previously enacted FIPs to allow states to continue participating in the Clean Air Interstate Rule’s emissions trading programs following its 2011 update as the Cross-State Air Pollution Rule (CSAPR). EPA is now replacing those FIPs with SIP revisions that similarly integrate CSAPR. Since October 2017, EPA has withdrawn FIPs and approved corresponding SIPs that rely on CSAPR to reduce regional haze for the following states: Georgia, Alabama, Kentucky, Virginia, Ohio, Tennessee, South Carolina, Missouri, West Virginia, and South Carolina.