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Regional Transport of Ozone

Information provided for informational purposes onlyNote: EPA no longer updates this information, but it may be useful as a reference or resource. See the latest information at the Ozone Implementation web site

Reducing the Regional Transport of Ozone (RTO) and ozone precursors (including nitrogen oxides or NOx) is necessary to help certain States attain the health standards for ground-level ozone (smog). Certain States were required to revise their State Implementation Plan (SIP) measures under EPA’s NOx SIP call to ensure that emissions reductions are achieved to mitigate the regional transport of ozone across State boundaries in the eastern half of the United States. Federal Implementation Plans (FIPs) may be needed to reduce regional transport if any State fails to adequately revise its SIP to comply with the NOx SIP call. In accordance with section 126 of the Clean Air Act, eight Northeastern States filed petitions requesting EPA to make findings and require decreases in NOx emissions from certain stationary sources in upwind States that may significantly contribute to ozone nonattainment problems in the petitioning State. The Ozone Transport Assessment Group (OTAG) was a partnership between the EPA, the Environmental Council of the States and various industry and environmental groups which assessed the long-range transport of ozone and ozone precursors.

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