Air News: Kenosha County's ozone nonattainment status reclassified

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Wisconsin Department of Natural Resources - Air Program

September 23, 2019

Kenosha County’s ozone nonattainment status reclassified

The U.S. Environmental Protection Agency (U.S. EPA) finalized a reclassification for a portion of Kenosha County from “moderate” to “serious” nonattainment for the 2008 ozone standard.

The affected portion of Kenosha County, shown shaded on the map, is the area inclusive of and east of Interstate 94. This area is the Wisconsin portion of the three-state (Illinois, Indiana, and Wisconsin) Chicago ozone nonattainment area for the 2008 standard.

The reclassification does not mean ozone pollution is worsening in Kenosha County. In fact, the long-term, three-year ozone design values in the county have been improving, from 84 ppb in 2010-2012 to 79 ppb in 2016-2018. This reclassification is required by the Clean Air Act because the area’s ozone levels did not meet the 2008 standard of 75 ppb by the required federal deadline (July 20, 2018).

The reclassification will take effect September 23, 2019 and will affect how air permitting is conducted in the eastern portion of the county. DNR is working with impacted facilities to explain any changes to the permitting process and to adjust existing permits as needed.

It is important to note that much of the ozone measured in Wisconsin is due to emissions originating from outside the state. Wisconsin’s lakeshore counties experience the highest ozone concentrations on warm days with southerly winds, which transport the compounds that cause ozone, especially volatile organic compounds (VOCs) and nitrogen oxides (NOx), into the state. VOCs and NOx react over Lake Michigan to form high concentrations of ozone, which is transported onshore by the lake breeze.

Overall, ozone levels statewide have decreased over the past 15 years and emissions of ozone precursors like VOCs and NOx have decreased by 50 percent since 2002.

For more information on ozone, EPA’s federal ozone standards and how ozone is measured in Wisconsin, visit the Air Program’s ozone webpage at -