Ozone Nonattainment Information
Proposed
Ozone Nonattainment Area -
Sublette County and Portions of Lincoln and Sweetwater Counties
CAUTION: SOME FILES MAY BE IN EXCESS OF 5 MB
In March 2008 the U.S. Environmental Protection Agency (EPA) promulgated a new National Ambient Air Quality Standard (NAAQS) for ozone. The ozone standard was lowered from 0.08 parts per million (ppm) to 0.075 ppm based on the fourth highest 8-hour average value per year at a site, averaged over three years. Based on monitoring results from 2006 through 2008, the entire state of Wyoming is in compliance with this standard except for at a single monitor, the Boulder monitor, in Sublette County. The Wyoming Department of Environmental Quality, Air Quality Division (AQD) evaluated whether a nonattainment area should be designated due to the monitored results at the Boulder monitor. The AQD recommended that the Upper Green River Basin (UGRB) be designated as nonattainment for the 2008 ozone National Ambient Air Quality Standard (NAAQS). The AQD based this recommendation on a careful review of the circumstances surrounding the incidence of elevated ozone events. Elevated ozone in the UGRB is associated with distinct meteorological conditions. These conditions have occurred in February and March in some (but not all) of the years since monitoring stations began operation in the UGRB in 2005.
On March 12, 2009, Governor Freudenthal submitted a recommendation to the U.S. EPA that the agency should designate the UGRB in southwest Wyoming as an ozone nonattainment area.
The AQD submitted a Technical Support Document to EPA on March 26, 2009, which described the technical analysis (and documentation: Appendix S.1, Appendix S.3, Appendix S.4A, Appendix S.4B, Appendix Glossary, Technical Support Document II) which supports the boundary selection of the proposed nonattainment area. The AQD submitted additional documentation to the EPA on May 19, 2009 and August 17, 2009. This information included a Legal Description of the Boundary, a Revised Boundary Figure, an Updated Trajectory Figures for Pages 56 to 86 in the Technical Support Document, and a Description and Trajectories for the March 8-12, 2008 Ozone Event.
On September 16, 2009, the U.S. EPA announced it would reconsider the 2008 standard for ground-level ozone. The EPA intends to propose any needed revisions to the ozone standards by December 2009 and issue a final decision by August 2010. The EPA also proposed to stay the 2008 standards for the purpose of attainment (meeting standards) and nonattainment (not meeting standards) area designations. During the stay, activity will not proceed on the UGRB proposed nonattainment area. EPA proposes to institute an accelerated ozone designation process for the reconsidered standards to be completed by August 2011.
On December 17, 2009, EPA extended their target date to propose a reconsidered ozone NAAQS until January 6, 2010.
On January 6, 2010, EPA proposed that the primary ozone standard be set between 0.060 and 0.070 ppm. The EPA also proposed a separate secondary standard for ozone. The EPA will accept public comment for 60 days after the proposed rule is published in the Federal Register. Additional information is available on the EPA website: http://www.epa.gov/air/ozonepollution/actions.html.
EPA has indicated that completing this rulemaking has taken longer than anticipated. EPA is committed to signing a final rule on the reconsideration of the 2008 Ozone standard by July 29, 2011.
EPA letter to Governors Office in regard to designation on December 8, 2011.
On April 30, 2012, Wyoming received a letter from EPA designating Sublette County and parts of Lincoln and Sweetwater Counties as non-attainment for ozone.
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