Interstate Air Pollution Transport
Interstate air pollution transport, or air transport, refers to emissions from upwind sources that impacts air quality in a given location downwind. The total pollution in any area forms from the combination of local emissions and emissions from upwind. Emissions of sulfur dioxide (SO2) and nitrogen oxides (NOX) can react 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 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