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Interstate Air Pollution Transport
Interstate air pollution transport, or air transport, is a combination of local emissions and emissions from upwind sources impacts air quality in any given location. Emissions of sulfur dioxide (SO2) and nitrogen oxides (NOX) can react in the atmosphere to form fine particle (PM2.5) pollution. Similarly, NOX emissions can react in the atmosphere to create ground-level ozone pollution. These pollutants can travel great distances affecting air quality and public health locally and 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. "Good neighbor" SIPs "contain adequate provisions - prohibiting, consistent with the provisions of this subchapter, any source or other type of emissions activity within the state from emitting any air pollutant in amounts which will... contribute significantly to nonattainment in, or interfere with maintenance by, any other state with respect to any such national primary or secondary ambient air quality standard."
EPA's Actions Under The "Good Neighbor" Provision
The EPA has taken actions to facilitate implementing the provisions of the "good neighbor" provision, including by administering the