Let’s Talk About Air Quality

Sustainability and Air Quality

The United States celebrates Earth Day this Wednesday, April 22. Governor Evers has declared the entire week “Earth Week" in Wisconsin. This is a good time to talk about air quality. The City of Madison updated its Sustainability Plan in 2025. The report mentions “air quality" fourteen times, with some references to indoor air quality and others to outdoor air quality. Perhaps because Madison enjoys consistently good air quality, the heavier emphasis in the plan is on decarbonization and preserving the quality of our wonderful lakes. 

In recent years Madison has endured a couple of air quality alerts in response to West Coast and Canadian wildfire smoke pollution. Those alerts are a reminder that Madison can't take our good air quality for granted. We need to monitor our air quality and plan transportation infrastructure and the built environment in ways that preserve our clean air. On March 17, the Common Council devoted a special session to Madison's sustainability efforts. One of the nine presentations was devoted to air quality. The report by Jessica Price and Gregg May of the Sustainability Staff reviewed how we measure air quality, Wisconsin's statutory obligations to manage air quality, and the new monitoring tools that Madison now has.

Measuring Air Quality

The US Environmental Protection Agency (EPA) measures and regulates air quality. It measures the presence of toxic gases and small particles in terms of their health impact. Small particles generated by combustion, agricultural tilling, mold, pollen, and construction can be particularly harmful, especially for people with respiratory sensitivities and diseases. Actual measurements are translated into a six-level air quality index (AQI) from “good" (little or no risk) to “hazardous" (declared health emergency). Here is the chart, which is generally recognized around the world.

Image credit: Madison Sustainability Staff

To fulfill its obligations under the Clean Air Act, the Wisconsin Department of Natural Resources (WDNR) maintains 36 regulatory complying monitors around the state. Two serve Madison and Dane County. Results from these monitors are available online. At the AirNow.gov website just enter your zip code. The app returns the index for the major pollutants, usually ozone and one or more particulate indices. More detailed and historic air quality data is available at this EPA website.

To supplement and refine the data from the two WDNR monitors, Madison took advantage of an EPA grant to install solar powered monitors. The Madison installation of 65 monitors appears on the following map.

Image credit: Love My Air Wisconsin

These monitors measure particulates. In March, the hourly data from the monitors became available to the general public. Use this link to the Love My Air Wisconsin website. Click on any dot on the map to get the current reading for that monitor. Click on the “View" button and get the hourly results for the past week.

Madison's Air Quality

Madison's generally “good" air quality is evident in the following table drawn from the EPA website for 2025.

Image credit: US Environmental Protection Agency data

Last year the Air Quality Index for Madison was “good" on 242 day (66%) and “moderate" on 116 days (32%). Only 7 days (2%) had higher indices and there were no days in the “very unhealthy" and “hazardous" categories. Note that on most days the primary pollutant was fine particulates. All other days it was ozone.

The new solar powered monitors have been telling the same story for the past month – “good" on most days and “moderate" on the rest. In fact, the AQI has rarely gotten above 20.

Preliminary Findings from Madison's New Monitors

Out of curiosity, I've been accessing the “Love My Air" site daily. Keeping in mind that these monitors only measure small particulates and there is only a month of data. Nevertheless, here are some preliminary observations:

• Neighborhood Differences: At any point in time, readings across the city are notably similar. On the whole the index is often higher on the Isthmus, but rarely by more than a few index points.
• Wind Direction and Speed: The average wind direction in Madison is from the south and southwest. However, from late fall to early spring, north, northwest, and west winds are frequent. So far, wind direction has not had an obvious impact. Wind speed may. There appears to be some correlation between gusty days and a greater prevalence of “moderate" index readings. Perhaps this can be attributed to dust blown up from surrounding tilled fields, which are generally bare at this time of year.
• Road Traffic Impacts: Since a major source of fine particles is combustion, I was curious whether monitor readings near the Beltline, Interstate and major arterials like University Avenue, Park Street, and Stoughton Rd might be higher. It does not appear to be the case. Similarly, depending on the wind direction, readings on the windward and leeward side of these thoroughfares does not appear to be significantly different.
• Urban Canyons: There are multiple peer-reviewed studies of the impact of urban canyons on the accumulation of pollutants. The usual definition I've seen for “urban canyons" is streets with aspect ratios of two or greater. That means streets where the weighted average of the height of the buildings on both sides is two or more times the width between the base of the buildings. The fact is that there are very few streets in Madison that meet this definition, except a few on the isthmus. Any such effect is not visible thus far in the data for the past month.