DNR Releases 2024 Air Quality Trends Report

MADISON, Wis. – The Wisconsin Department of Natural Resources (DNR) today released its annual air quality trends report. This year’s report covers 20 years of state air monitoring data for air pollutants regulated under the Clean Air Act, including ground-level ozone, sulfur dioxide, nitrogen dioxide, carbon monoxide, particle pollution and lead. The report presents data from the 2023 calendar year, including the historic 2023 Canadian wildfire smoke events.

According to the Canadian Interagency Forest Fire Center, 15 million hectares (about two million acres larger than the state of Wisconsin) burned in 2023 – more than six times the annual average in Canada.

“Five percent of the entire Canadian forest burned last year,” said Gail Good, DNR Air Management program director. “During the multi-day air quality advisory in late June of last year, the air monitoring network measured some of the highest PM_2.5 concentrations ever recorded in the state.”

Wildfire smoke events in 2023 resulted in the DNR issuing 15 PM_2.5 air quality advisories – almost five times higher than the average over the previous 12 years. PM_2.5 advisories are issued when air quality has reached or is expected to reach the orange “unhealthy for sensitive groups” level on the Air Quality Index (AQI).

The design values used to assess PM_2.5 concentrations are calculated over a three-year period. This year’s Trends Report shows an increase in PM_2.5 concentrations for the most recent period (2021-2023). Despite the jump caused by 2023’s wildfire smoke, overall, PM_2.5 concentrations have decreased 25% in the last 20 years, and all monitors measured concentrations below the 2012 federal air quality standards.

The report shows that over the last 20 years, statewide ozone concentrations have decreased by 15%. For decades, ozone concentrations have been dropping across the state. However, that trend has slowed. Last year’s wildfire smoke contained ozone-forming pollutants, which, combined with recent warmer-than-usual summers, contributed to increased ozone concentrations.

As a result, the Lake Michigan shoreline area, including the Milwaukee area and parts of Sheboygan and Kenosha counties, continues to fall short of meeting the 2015 ozone standard. Wisconsin has implemented many programs that have reduced emissions of ozone-causing pollutants from power plants, industry and transportation in the state. However, these emission reductions have not resulted in the attainment of the 2015 ozone standard because most ozone-causing emissions are transported across state boundaries and are outside Wisconsin’s control.

To better illustrate the latest trends, the DNR updated its Air Quality Trends Report Interactive StoryMap, which shows Wisconsin's air quality trends for each pollutant over the last 20 years. This tool provides an interactive visual to help convey the complex air quality data.

The 2024 Air Quality Trends Report, StoryMap and other historical reports are available on the DNR’s Air Quality Trends webpage. Current Wisconsin air quality conditions can be found on the Wisconsin Air Quality Monitoring Data webpage.