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Interstate Air Pollution Transport

Interstate Air Pollution Transport

What's New
  • January 22, 2015 - EPA issued a memo (PDF 1p) and preliminary air quality modeling data (PDF 155 pp) that will help states as they develop State Implementation Plans to address cross-state transport of air pollution for the 2008 ozone standards. For more information visit Transport for the 2008 Ozone NAAQS.

  • November 21, 2014 - EPA issued a ministerial rule (PDF 53 pp) that aligns the dates in the CSAPR rule text with the revised court-ordered schedule, including 2015 Phase 1 implementation and 2017 Phase 2 implementation. In a separate ministerial action, EPA issued a NODA (PDF 8 pp), as required by CSAPR, that aligns the final CSAPR default allowance allocation years with the revised court-ordered schedule.
  • 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 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 NOX Budget Trading Program, the Clean Air Interstate Rule, and the Cross-State Air Pollution Rule. Most recently, CSAPR addresses pollution transport for the 1997 ozone NAAQS, 1997 PM2.5 NAAQS, and 2006 PM2.5 NAAQS. As appropriate, EPA will work with our state partners to develop paths forward to address transport for newer NAAQS

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