Ozone pollution is a public health hazard and a complex problem for states, power plants, and industrial facilities that generate ground-level ozone.
The U.S. Environmental Protection Agency (EPA) recently lowered the ozone air quality standard, leaving states and EPA to grapple with which areas to designate as out of compliance with this standard. Wisconsin ultimately convinced EPA to follow its recommendation to limit the size of the nonattainment areas in the state. Time will tell if the reduced ozone air standard and nonattainment designations will affect air quality or profit margins.
Clean Air Act Regulation of Ozone
EPA has regulated ground-level ozone as a pollutant under the Clean Air Act since 1971.
Ozone is formed from when nitrous oxides (NOx) and volatile organic compounds (VOCs) – so-called ozone precursors – react in sunlight. Increased ozone formation in sunlight means that ozone levels are higher in the summer. High concentrations of ground-level ozone cause respiratory and cardiac problems. The Clean Air Act limits ground-level ozone pollution by regulating the quantity of NOx and VOCs emitted by motor vehicles, power plants, and other industrial facilities.
The Clean Air Act requires EPA to set National Ambient Air Quality Standards (NAAQS) for certain pollutants such as ground-level ozone to protect the health of sensitive populations like children, the elderly, outdoor workers, and asthma sufferers. EPA must revise and update these standards periodically as research advances and as scientists discover that even lower concentrations of pollutants can impact public health.
Once EPA issues new NAAQS for a pollutant, EPA has two years to review air monitoring data to determine which areas meet the new NAAQS. States and tribes propose compliance designations for areas within their boundaries based on air monitoring data and modeling. EPA reviews submitted data and makes one of the following designations:
- areas in compliance with the new standard are designated as attainment;
- areas not in compliance are designated as nonattainment; and
- areas that cannot be classified are either designated as unclassifiable or as attainment/unclassifiable.
EPA is required to designate a nonattainment area if an air quality monitor in that area exceeds the NAAQS or if that area is contributing to a NAAQS violation in a nearby area.
Areas of Attainment and Nonattainment
Areas designated nonattainment for any NAAQS are subject to stricter federal regulations than are areas designated as attainment. For any nonattainment area, states must develop and obtain EPA approval for a plan that:
- inventories sources of emissions;
- imposes stricter pollution control requirements for major emission sources; and
- demonstrates how the state will make reasonable further progress toward attainment of the NAAQS.
For areas designated as nonattainment of the ground-level ozone NAAQS, the requisite emission reductions for pollution sources become stricter as an area deviates further from compliance with the air standard.
States must also develop and implement vehicle inspection and maintenance programs for ozone nonattainment areas.
The Cross State Air Pollution Rule
Even though states are responsible for achieving and maintaining compliance with ozone standards, we know that ozone and its precursors – NOx and VOCs – travel across state and jurisdictional boundaries. In 2011, EPA promulgated the Cross State Air Pollution Rule to address this issue and to help states comply with the “good neighbor” provision of the Clean Air Act.
The Cross State Air Pollution Rule requires some states in the eastern half of the U.S., including Wisconsin, to limit NOx emissions from power plants in the summer months when ozone levels are at their highest. EPA calculates a state’s summer budget of power plant NOx emissions based on how much that state’s NOx emissions contribute to ozone levels in nearby states.
EPA revised the NAAQS for ground-level ozone in 2015 based on new evidence of health impacts at lower ozone levels. The 2015 ozone NAAQS is 70 parts per billion (ppb), reduced from the 2008 standard of 75 ppb. After EPA failed to issue compliance designations by the 2017 deadline, several states – not including Wisconsin – and environmental and public health organizations sued EPA to force it to determine which areas were in or out of compliance with the new standard. The court ruled that EPA had to designate most areas of the country as attainment or nonattainment for the new ozone standard by April 30, 2018.1
Wisconsin’s Ozone Levels
Designations of attainment or nonattainment of the ozone standard are based on air quality data from a three-year period preceding the designation.
Wisconsin samples air quality at 30 monitoring locations throughout Wisconsin. Between 2014 and 2016, the only monitors in Wisconsin that exceeded the 2015 ground-level ozone NAAQS were those along the Lake Michigan shoreline in Door, Kenosha, Manitowoc, Milwaukee, Ozaukee, and Sheboygan counties. The ozone levels at these violating monitors ranged from 71 ppb to 79 ppb, with the highest ozone levels recorded at the Kohler-Andrae monitor in Sheboygan along the Lake Michigan shoreline.2
Emissions in other states contribute to ozone pollution in Wisconsin, and Wisconsin’s emissions also travel to other states. The higher observed ozone levels in southeast Wisconsin are attributed in part to emissions from states to the southeast and the unique meteorological conditions along Lake Michigan.
In response to concerns about the regulatory impact of a nonattainment designation and the localized high ozone concentrations along Lake Michgan, the Wisconsin Legislature decided to eliminate the Sheboygan County monitor along the lakeshore and instead rely on an air monitor further inland. In 2018, Wisconsin passed a law that requires DNR to exclude the Kohler-Andrae monitor in Sheboygan from the air monitoring network that the State and EPA use to determine compliance with the NAAQS.3
Ozone Designations in Wisconsin
Counties in southeast Wisconsin have been in and out of attainment with the ozone standard for decades. Even though ozone concentrations have decreased, EPA has also incrementally lowered the ozone standard as we learn more about the negative health effects of ozone. Under the previous 2008 ozone NAAQS, only Sheboygan County and a portion of Kenosha County were designated nonattainment.
On Sept. 21, 2016, Governor Scott Walker recommended that EPA designate all areas of Wisconsin as attainment for the 2015 ozone standard. In 2017, DNR sent a supplemental technical support document to EPA in support of the Governor’s request. DNR proposed that EPA either adopt the Governor’s request to designate all of Wisconsin as attainment or designate only a small area along the Lake Michigan shoreline as nonattainment. DNR based this recommendation on Wisconsin’s improved ozone levels, reduced ozone emissions, and other states’ contribution to ozone pollution in Wisconsin. DNR also noted that Wisconsin’s higher ozone levels are limited to the Lake Michigan shoreline, which DNR attributed to inland lake breezes of ozone-rich air transported from southern states.
In the end of 2017, EPA proposed to designate most of Wisconsin as attainment, but proposed nonattainment designations for Milwaukee, Ozaukee, Racine, Washington, and Waukesha counties, and for part of Kenosha, Door, Manitowoc, and Sheboygan counties. EPA proposed to designate these areas nonattainment because they either contained violating air monitors, contributed to a violation at a nearby monitor, or both. DNR responded to EPA’s proposed designations in early 2018, and disputed EPA’s rationale for designating this larger portion of southeast Wisconsin as nonattainment.
EPA issued its final ozone designations for Wisconsin on May 1, 2018, which designated as nonattainment an area between 2 to 5 miles inland of the lakeshore in Kenosha, Door, Manitowoc, Sheboygan, Milwaukee, and Ozaukee counties. EPA cited DNR’s data and analysis to support its finding that only this smaller area along the lakeshore exceeded or contributed to an exceedance of the 2015 ozone air quality standard.
What This Means for Wisconsin
Following EPA’s ozone area designations for Wisconsin, the state must develop a plan to demonstrate how it will bring these nonattainment areas into compliance.
Compared to the designations under the 2008 standard, Wisconsin has more counties with partial nonattainment areas, though less of Sheboygan County is nonattainment. Compared to EPA’s proposed designations in late 2017, EPA’s final rule granted Wisconsin a significant reprieve from the additional regulation that would have been imposed on a larger portion of southeast Wisconsin.
It remains uncertain how nonattainment designations in Wisconsin and throughout the region may affect emission budgets for Wisconsin and neighboring states under the Cross State Air Pollution Rule. Also uncertain is how these regulatory changes will affect Wisconsin’s ozone levels, air quality, and public health in the years to come.
1 In re Ozone Designation Litigation, 286 F. Supp. 3d 1082, 1087 (N.D. Cal. 2018).
2 Wisconsin Department of Natural Resources, 2015 Ozone National Ambient Air Quality Standards: Technical Support Document at 7 (April 2017).
3 2017 Wis. Act. 159.