Ozone Standards and Nonattainment Designations

Ground-level ozone's harmful effects on human health and the environment prompted the federal government to set air quality standards for the amount of ozone in the air over certain time periods. Counties that do not meet these standards receive a nonattainment designation that triggers increased pollution control requirements for businesses in the area, along with other efforts to reduce ozone levels. Several counties in eastern Wisconsin are currently designated as nonattainment areas under federal rules.

Gov. Doyle's letter to EPA on ozone nonattainment - On March 12, 2009, Gov. Doyle wrote to EPA, recommending the agency designate all Wisconsin counties as attainment for the 8-hour ozone standard. 3/16/2009

• Letter [PDF 102KB]
• Appendix [PDF 57KB]

This page includes an overview of ozone standards and links to more information about nonattainment designation.

Ozone Nonattainment

When a county is identified as not meeting a federal air quality standard based on monitored values of the outside air, it is designated by the U.S. Environmental Protection Agency as nonattainment and given a target date to meet the standard. State plans are then prepared that include regulations for controls on emissions that are needed to reduce the air pollution and meet the standard. If at any time monitored values show that the air quality has improved and the county now meets the standard, the DNR can request redesignation of the county. Currently, ten counties in eastern Wisconsin are designated as nonattainment, though the DNR has petitioned U.S. EPA to redesignate eight of the counties.

Find more information, including maps and details of the 2007 redesignation request, on our Ozone Nonattainment Areas page.

Overview of Ozone Standards

The federal Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to develop two types of air quality standards for key air pollutants:

• Primary standards protect public health, including the health of groups especially affected by air pollution, such as asthmatics, children and the elderly.
• Secondary standards protect public welfare and the environment, including protection against damage to animals, crops and buildings.

EPA is required to set a primary standard at a level that protects public health with an adequate margin of safety. EPA is required to set a secondary standard at a level that protects public welfare and the environment from any known or anticipated adverse effects.

In 1997, EPA revised the ozone standard and set the primary standard to 0.08 parts per million (ppm) for an 8-hour average (that is, the average of ozone levels recorded over an 8-hour period cannot exceed 0.08 ppm). The secondary standard is currently the same as the primary standard for ozone. For more details see EPA’s Web site on the National Ambient Air Quality Standards [exit DNR].

One determines whether a violation of the standard occurs by first calculating the “design value” for each monitoring location, then comparing that to the 0.08 ppm standard. The design value is the average over a three-consecutive-year period of the fourth-highest concentration in each year. These design values are then compared to the level of the standard, 0.08 ppm, to determine if ozone levels at any monitoring location have violated the standard during the period in question.

Find links to current and historical data on ozone levels in Wisconsin on the Ozone Resources and Air Monitoring Data page.

For more on specific regulatory requirements related toozone standards, visit the Ozone Control Strategies and Regulations page.