EPA Determines Phoenix-Mesa Would Have Met 2015 Ozone Standards But for International Emissions

The U.S. Environmental Protection Agency (EPA) has issued a final rule determining that the Phoenix-Mesa nonattainment area in Arizona would have attained the 2015 ozone National Ambient Air Quality Standards (NAAQS) by the August 3, 2024 Moderate area attainment deadline, were it not for ozone-forming emissions originating outside the United States — primarily transboundary pollution from international sources. Because the failure to meet the standard is attributed to international emissions beyond the area's control, EPA is invoking the Clean Air Act's 'but for' provision, which shields areas from reclassification penalties when attainment failure is caused by foreign emissions. As a result, Phoenix-Mesa retains its classification as a 'Moderate' nonattainment area and is not reclassified to 'Serious,' which would have triggered more stringent requirements. This final action also relieves Arizona of certain regulatory obligations. The State is no longer required to submit attainment contingency measures or reasonable further progress (RFP) contingency measures for the Phoenix-Mesa area, reducing the administrative and regulatory burden on state air quality agencies. The ruling fulfills EPA's statutory obligation under the Clean Air Act to make an attainment determination following the attainment deadline. It reflects an acknowledgment that local and state-level pollution controls alone cannot fully offset the impact of transboundary international air pollution on regional ozone levels.

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