Why Midwestern Cities Faced America’s Most Unhealthy Air This Summer

DETROIT, Mich. - Midwest summers are known for state fairs, days on the lake, and, in this state, cherries. This year, however, wildfire smoke has been an unwelcome addition. Among America's biggest counties, the most persistent smoke this summer has been concentrated in the Midwest.

A new Direct Relief analysis found that 16 of the 18 U.S. counties with more than 500,000 residents experiencing the most medium-or-heavier smoke days were in the Midwest. Direct Relief analyzed 77 consecutive days of NOAA satellite smoke data from June 1 through Aug. 16, along with EPA air-quality monitoring data and federal wildfire records.

Hennepin and Ramsey counties in Minnesota led with 34 smoke days each. Dane County, Wisconsin, recorded 29, while populous counties encompassing Detroit, Chicago, Milwaukee and other Midwestern cities experienced roughly four weeks of smoke overhead. Spokane County, Washington, and Ada County, Idaho, were the only Western counties among the top 18.

The scale of exposure extends well beyond those cities. About 223 million people, equal to approximately 65% of the population, lived in U.S. counties that experienced at least 10 days of medium-or-heavier smoke during the period analyzed. Heavy smoke was detected somewhere over North America on 76 of the 77 days studied.

This year's wildfires in the U.S., which have occurred mostly in western states, have burned more than 7.2 million acres, which is 169% of the year-to-date average of the past decade

While some of the Midwest smoke originated from Western wildfires, closer Canadian wildfires have repeatedly sent smoke south across the border this summer as well. NASA satellite imagery captured smoke from Ontario fires spreading over Canada and the United States in mid-July, while Michigan environmental officials attributed a multi-day air-quality emergency to smoke from ongoing Canadian wildfires.

The Canadian wildfires in mid-July led to some of the worst air quality globally. On July 16, West Duluth, Minnesota, recorded the highest PM2.5 air-quality reading in Direct Relief's summer analysis. That day's air quality index of 964 was more than 8.5 times as high as the 2025 average for the city with the world's worst air quality, based on IQAir data.

PM2.5 refers to particulate matter measuring 2.5 micrometers or less in diameter. These microscopic particles are a major health concern because they can penetrate deep into the lungs, and some can enter the bloodstream. Exposure to particle pollution has been linked to aggravated asthma, decreased lung function, heart attacks, and premature death, particularly among people with existing heart or lung disease, according to the EPA.

Satellite observations can detect smoke high in the atmosphere, but do not necessarily show what people are breathing at ground level. Direct Relief's analysis found a strong overlap between smoke overhead and unhealthy air below. Across 438 EPA monitoring sites, there were 1,165 days when PM2.5 reached "Unhealthy" levels or worse, and more than 98% of those readings occurred while satellite data also showed a smoke plume overhead.

As wildfires and smoke affect more of the country, Direct Relief is prepared to respond in multiple ways, providing respirators, resilient power systems, and medications and therapies needed for wildfire-related health issues through its existing partner network.

Map and Analysis by Mila Dorji and the Direct Relief DMI Team