As air quality is increasingly recognized as a critical public health issue, a new analysis reveals that Michigan is among the top 10 states with the most counties ranking highest for worst air quality.

The analysis, based on 2023 air quality data from the United States Environmental Protection Agency for 950 U.S. counties, found that Michigan ranked # 7 among states with the most counties having poor overall air quality based on the following scoring system:

  • Unhealthy for Sensitive Groups Days: 1 point
  • Unhealthy Days: 2 points
  • Very Unhealthy Days: 3 points
  • Hazardous Days: 4 points

Here is the list of the top 10 states with the most counties on the list:

  1. Illinois – 17 counties
  2. Wisconsin – 15 counties
  3. California – 9 counties
  4. Iowa – 6 counties
  5. Pennsylvania – 6 counties
  6. Indiana – 5 counties
  7. Michigan – 5 counties
  8. Ohio – 5 counties
  9. Minnesota – 5 counties
  10. Missouri – 4 counties

Here’s a deeper look at the five Michigan counties ranking in the top 100 for worst air quality:

#11 Wayne County Air Quality

Wayne County recorded 15 "Unhealthy for Sensitive Groups" days, 7 "Unhealthy" days, 0 "Very Unhealthy" days, and 0 "Hazardous" days in 2023.

As one of Michigan's most industrialized regions, Wayne County faces significant air quality challenges due to high traffic and numerous industrial facilities emitting pollutants like particulate pattern, sulfur dioxide (SO2), nitrogen oxides (NOx) and volatile organic compounds (VOCs). The county earned an “F” from the American Lung Association in its 2024 State of the Air report. Power plants and cross-border pollution from Canada are also contributing. The county struggles with high ozone levels and particulate matter, leading to increased respiratory and cardiovascular issues, particularly among vulnerable populations. Residents are often advised to limit outdoor activities on poor air quality days.

Here are some key metrics for Wayne County:

#45 Lenawee County Air Quality


Lenawee County recorded 9 "Unhealthy for Sensitive Groups" days, 4 "Unhealthy" days, 1 "Very Unhealthy" day, and 0 "Hazardous" days throughout 2023.  

Rural Lenawee County faces air quality challenges due to agriculture, local industries and regional pollution. Agricultural practices can contribute to air pollution through machinery, fertilizers and livestock, releasing ammonia and particulate matter. Dust from fieldwork can further impact air quality. While not heavily industrialized, the county has several manufacturing plants emitting pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs), which can form ground-level ozone. Pollutants from nearby urban areas like Toledo and Detroit impact air quality, particularly during certain wind patterns, especially in summer. Despite these issues, Lenawee County remains in attainment for all pollutants under the Clean Air Act.

Here are some key metrics for Lenawee County:

#66 Allegan County Air Quality

Allegan County recorded 11 "Unhealthy for Sensitive Groups" days, 3 "Unhealthy" days, 0 "Very Unhealthy" days, and 0 "Hazardous" days throughout last year in 2023.

Allegan County is primarily rural and faces air quality challenges from agricultural activities, local industries and pollution from nearby areas. Extensive farming operations contribute to air pollution through machinery, fertilizers, and livestock emissions, which release ammonia and particulate matter. Dust from fieldwork further impacts air quality. The county’s permitted air sources emit nitrogen oxides (NOx) and volatile organic compounds (VOCs), which can form ground-level ozone. Pollution from surrounding urban areas also worsens local conditions, particularly in warmer months. 

Here are some key metrics for Allegan County: 

#67 Washtenaw County Air Quality

Washtenaw County recorded 9 "Unhealthy for Sensitive Groups" days, 4 "Unhealthy" days, 0 "Very Unhealthy" days, and 0 "Hazardous" days in 2023.

Washtenaw County faces air quality challenges from local traffic, industries and regional pollution. Vehicle emissions contribute significantly to ground-level ozone and particulate matter (PM2.5) pollution, especially during warmer months. The county also has manufacturing facilities that release pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs), which can lead to ozone formation. Pollution from nearby urban areas, such as Detroit and Ann Arbor, can affect air quality, particularly during certain weather conditions. 

Here are some key metrics for Washtenaw County:

#86 St. Clair County Air Quality

St. Clair County recorded 7 "Unhealthy for Sensitive Groups" days, 4 "Unhealthy" days, 0 "Very Unhealthy" days, and 0 "Hazardous" days in 2023.

St. Clair County faces air quality challenges primarily due to industrial activities, local traffic and cross-border pollution from nearby Sarnia’s “Chemical Valley” in Canada. The county’s industrial facilities, including chemical plants and manufacturing units, release pollutants like sulfur dioxide (SO2), nitrogen oxides (NOx), and volatile organic compounds (VOCs), contributing to ground-level ozone and particulate matter (PM2.5) pollution. 

Here are some key metrics for St. Clair County:

Here’s a look at the entire dataset:

Air Pollution Top 100 Counties

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Nina Misuraca Ignaczak is an award-winning Metro Detroit-based editor, journalist, and documentary filmmaker. She is the founder, publisher, and editor of Planet Detroit, a digital media startup focused on producing quality climate, equity, health, and environment journalism that centers grassroots voices, holds power accountable, and spotlights solutions. Planet Detroit has received awards and recognition from the Society for Professional Journalists Detroit, the Institute for Nonprofit News, and LION Publishers since its establishment in 2019. Prior to her journalism career, Nina worked in urban planning in local government and nonprofit sectors, holding a Master of Science in Natural Resource Ecology and a Bachelor of Science in Biology from the University of Michigan, Ann Arbor.