On March 3, 2023, the D.C. Circuit Court of Appeals rejected an industry challenge to the April 2021 Revised Cross-State Air Pollution Rule (CSAPR) Update Rule from the Environmental Protection Agency (EPA or Agency), which required power plants in 12 “upwind” states to reduce nitrogen oxide (NOx), an ozone precursor, emissions such that those states did not inhibit downwind states’ ability to comply with the 2008 Ozone National Ambient Air Quality Standard (NAAQS).
EPA first issued the CSAPR Update Rule to address the 2008 ozone NAAQS Good Neighbor obligations in September 2016. The D.C. Circuit remanded the CSAPR Update Rule back to the Agency and vacated EPA’s subsequent “CSAPR Close-Out” Rule. The court ultimately ordered EPA to finish the revised rule ahead of the July 20, 2021, serious attainment deadline for downwind states.
The Midwest Ozone Group (MOG) challenged EPA’s analytical approach to its four-step framework under the Good Neighbor Provision of the Clean Air Act in promulgating the Update Rule. The Good Neighbor Provision requires each upwind state to issue plans that restrict its emissions that will “contribute significantly” to nonattainment or interfere with maintenance in any downwind state with respect to a NAAQS. EPA has developed the following four-step framework to address Good Neighbor obligations:
- Identify downwind receptors projected to have trouble attaining or maintaining the NAAQS in the relevant year.
- Determine which upwind states emissions are “linked” to the downwind receptor(s) by contributing above a threshold amount to downwind nonattainment/maintenance problems.
- For linked states, identify upwind emissions that contribute significantly to downwind nonattainment or interfere with maintenance, including by evaluating whether highly cost-effective control measures are available to address air quality at the downwind receptor.
- For upwind states with emissions that contribute significantly to downwind nonattainment or interfere with maintenance, EPA may develop a rule directing states adopt plans to implement necessary measures.
Among other arguments, MOG contended that EPA deviated from past air quality modeling practices in Step 1, used existing modeling data rather than conduct new modeling for Step 2, and arbitrarily determined control requirements for the units subject to the rule in Step 3.
The court rejected MOG’s contentions and upheld the rule, holding that EPA had adequately explained its techniques and operated reasonably under tight deadlines and that MOG had failed to demonstrate states would have been regulated differently under other analytical methods.
Under the Revised CSAPR Update Rule, EPA required emissions reductions from power plants in the following 12 upwind states through the 2024 ozone season: Illinois, Indiana, Kentucky, Louisiana, Maryland, Michigan, New Jersey, New York, Ohio, Pennsylvania, Virginia, and West Virginia.
 See 42 U.S.C. § 7410(a)(2)(D)(i).
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