2024 Wisconsin Air Quality Trends Report

Wisconsin Department of Natural Resources

Report Overview

Each year, the Wisconsin Department of Natural Resources (DNR) releases an Air Quality Trends report that shares official state monitoring data for air pollutants regulated under the Clean Air Act.

This StoryMap is intended to complement the DNR’s  Annual Trends Report  and provides an interactive look into the monitored air quality trends throughout Wisconsin over the past 20 years. Both the 2024 Trends Report and the accompanying StoryMap include monitoring data through 2023.

Explore the map to the right by hovering your mouse over or clicking on the monitoring site locations to see air monitoring station information from around the state.

Throughout the Trends Report and this StoryMap, users will see trends in air quality represented by trends in Design Values (DVs). A DV is a statistic used to show representative air quality for a particular region relative to the National Ambient Air Quality Standards (NAAQS).  

The NAAQS are a set of standards set by the Environmental Protection Agency (EPA) as required by the Clean Air Act to protect public health and the environment.

For more information on DVs and NAAQS values, visit the  EPA website .


Criteria Pollutants

Concentrations of most pollutants regulated under the Clean Air Act have been decreasing across Wisconsin since the early 2000s. While PM 2.5  and ozone concentrations have generally decreased for decades in Wisconsin, downward trends have slowed in recent years. The majority of Wisconsin meets federal standards for every criteria pollutant except ozone, where three nonattainment areas remain along the Lake Michigan shoreline.

The maps below allow the user to navigate through 20 years of criteria pollutant design values to visualize air quality trends in Wisconsin.

Press the play button located near the bottom of each map to begin the animation. Clicking on counties that contain monitoring stations will bring up a time-series graph that spans the entire animation for each site within that county (right-click to enlarge the image by opening it in a new tab).

Ozone (O 3 )

Ozone (O 3 ) is a highly reactive gas compound composed of three oxygen atoms. Ozone forms via chemical reactions in the atmosphere between pollutants such as nitrogen oxides (NO x ) and volatile organic compounds (VOCs) in the presence of sunlight. Temperature changes from the shoreline to the lake can create pressure differences, which causes a lake breeze that pushes ozone formed over the lake onto the shore. Wisconsin’s unique geography along Lake Michigan makes it susceptible to transported air pollution, leading to elevated ozone levels along the lakeshore. Exposure to high levels of ozone can aggravate lung diseases, damage airways and increase the frequency of asthma attacks.


PM 2.5 

PM 2.5  is composed of inhalable particles with a diameter of 2.5 micrometers and smaller, making the largest of these particles roughly 30 times smaller than the width of a human hair. The primary source of PM 2.5  is combustion such as gas engines and coal and natural gas power plants. Since PM 2.5  is so small, these particles can make their way deep into the respiratory system and eventually into the bloodstream. Health effects associated with exposure to PM 2.5  include increased rates of respiratory diseases and depressed lung functionality.


SO 2 

Sulfur dioxide (SO 2 ) is part of a larger group of highly reactive gases known as oxides of sulfur and makes its way into the air via combustion. The primary source of SO 2  is the burning of fossil fuels within industrial facilities. Exposure to SO 2  can cause and exacerbate several adverse respiratory effects in vulnerable populations including those with asthma and especially children.


NO 2 

Nitrogen dioxide (NO 2 ) is one of a group of highly reactive gases known as oxides of nitrogen. The primary source for NO 2  is the burning of fossil fuels. Fossil fuels are burned to produce electricity, power industrial operations and power motor vehicles. Vehicle exhaust is the largest source of NO 2  emissions. This results in the highest concentrations of NO 2  occurring in the immediate vicinity of busy roadways. Short-term exposure to NO 2  can aggravate respiratory symptoms such as wheezing, coughing or difficulty breathing. Prolonged exposure to NO 2  is linked to the development of asthma as well as increased rates of respiratory infection.


Stay up to date on air quality in Wisconsin using the interactive map below

Real Time Wisconsin Air Quality