Interstate Air Pollution Transport
The total pollution in any area forms from the combination of local and upwind sources. Air transport refers to pollution from upwind emission sources that impact air quality in a given location downwind. Emissions of sulfur dioxide (SO2) and nitrogen oxides (NOX) can each undergo chemical reactions in the atmosphere to form fine particle (soot) pollution. Similarly, NOX emissions can react in the atmosphere to create ground-level ozone (smog) pollution. These pollutants can travel great distances affecting air quality and public health regionally. The transport of these pollutants across state borders, referred to as interstate air pollution transport, makes it difficult for downwind states to meet health-based air quality standards for PM2.5 and ozone.
The "Good Neighbor" Provision
The Clean Air Act's "good neighbor" provision requires EPA and states to address interstate transport of air pollution that affects downwind states' ability to attain and maintain National Ambient Air Quality Standards (NAAQS). Specifically, Clean Air Act section 110(a)(2)(D)(i)(I) requires each state in its State Implementation Plan (SIP) to prohibit emissions that will significantly contribute to nonattainment of a NAAQS, or interfere with maintenance of a NAAQS, in a downwind state. The Act requires EPA to backstop state actions by promulgating Federal Implementation Plans (FIPs) in the event that a state fails to submit or EPA disapproves good neighbor SIPs.
EPA's Actions Under The "Good Neighbor" Provision
The EPA has taken actions to facilitate implementing the provisions of the "good neighbor" provision, including the
- NOX Budget Trading Program (2003-2008)
- Clean Air Interstate Rule (2009-2014)
- Cross-State Air Pollution Rule (2015-present)
- (Begins 2017), which updates the CSAPR ozone season NOX program.
- 2015 Ozone NAAQS (Notice of Data Availability - Preliminary Interstate Ozone Transport Modeling Data for the 2015 Ozone NAAQS) (signed December 2016)
Memo and Supplemental Information on Interstate Transport SIPs for the 2008 Ozone NAAQS (signed October 2017)