Regulatory Tracker

Air Transport – Cross-State Air Pollution Rule / Good Neighbor Rule, Section 126 Petitions, and Section 184 Ozone Transportation Commission Petition

Click here to return to our Regulatory Tracker or here to sign up for our monthly Tracker email updates. If you’re a reporter and would like to speak with an expert on this rule, please email us.

For information on EPA’s National Ambient Air Quality Standards (NAAQS) scientific review and approval process read our NAAQS Regulatory Tracker page here. To follow EPA’s work on the Ozone NAAQS, see our Ozone NAAQS Regulatory Tracker page here and for information on the PM NAAQS, see our PM NAAQS Regulatory Tracker page here.

Why it Matters

The Clean Air Act’s (CAA) “Good Neighbor” provision requires upwind states to ensure that the air pollution they create does not affect downwind states’ ability to meet the NAAQS. Downwind states rely on this provision to protect their residents’ health. States are required to address interstate pollution in their State Implementation Plans (SIPs) for implementing the NAAQS.

A downwind state can file a CAA section 126 petition asking EPA to regulate pollution from sources in another state when that pollution is moving across state lines and impairing interstate air quality. Additionally, section 176A of the CAA authorizes EPA to establish a transport region of states that contribute significantly to a NAAQS violation. Section 184 established such a region for ozone—the Ozone Transport Region (OTR)—for the northeast and mid-Atlantic and requires certain control requirements to address interstate ozone pollution transport within the OTR.

To address regional transport in the eastern half of the US, EPA established the Cross-State Air Pollution Rule (CSAPR) to require upwind states to reduce interstate pollution of soot and smog contributors, sulfur dioxide (SO2), and oxides of nitrogen (NOx), and ensure downwind states can meet the NAAQS for the 2008 ozone standard. EPA is now working to finalize the Good Neighbor Plan to address air transport related to the 2015 ozone standard.

Current Status

We will continue to update this map as courts issue decisions.


In 2020, in response to section 126 petitions, the D.C. Circuit denied Delaware’s petition, granted Maryland’s petition in part, and vacated EPA’s denial of New York’s petition and returning the petition to EPA for reconsideration.

A group of eastern states and D.C. also asked EPA in 2020 under section 184(c) to require Pennsylvania to further regulate its coal-fired power plants. EPA held a public hearing on February 2, 2021 and released information that it believed “may be relevant in reaching a decision on the recommendation.” Comments were due April 7, 2021.

On March 15, 2021, the Biden EPA issued a final rule updating the CSAPR for the 2008 ozone NAAQS, which EPA states resolves 21 states’ outstanding interstate ozone transport obligations with respect to the 2008 ozone NAAQS. This rule was in response to the D.C. Circuit’s remand of the CSAPR Update in Wisconsin v. EPA and also responds to the D.C. Circuit vacatur of the CSAPR Close-Out in New York v. EPA. The court had determined that the CSAPR Update rule was unlawful as it would have allowed states to continue their significant contributions to downwind ozone problems beyond their attainment dates.

For the transport related to the 2015 ozone NAAQS, EPA published its proposed Good Neighbor Plan for power plants in certain states as well as new NOx emission limits for certain industrial sources on April 6, 2022Comments were due on June 21, 2022.

On March 15, 2023 EPA published the final Good Neighbor Plan Rule, which implements NOx limits on power plants and industrial sources (for the first time) in 23 states. The Rule carries forward previous interstate air pollution program cap-and-trade programs for power plants, with several revisions including dynamic budgets and annual recalibration of the allowance bank. It also includes backstop emissions rates and flexibilities to ensure states meet the 2015 ozone NAAQS attainment deadlines, without compromising electric grid reliability. Read our summary of the rule here: 2023 Good Neighbor Plan.

Air Transport Rules

Air Transport Rules History: Cross-State Air Pollution Rule / Good Neighbor Rule

Section 126

Section 184(c) – Ozone Transportation Commission Petition