SmogRank / Episodes / United States
Illinois and Iowa, United States, March 2026
For 2 days, from 4 to 5 March 2026, 23 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Brookfield, Illinois, United States: 32.4 µg/m³ on 4 March, about 4.3× its usual 7.5.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 23 in 1 country
Days 2 4 to 5 March 2026
Worst day 4 March 17 cities counted
Furthest above usual 4.8× Clinton
Day by day
Play 4 March 17 cities at twice their usual or more
Madison Elgin Cary Wheaton Waukesha Peoria Brookfield Des Plaines Zion Northbrook Park Ridge Niles South Milwaukee Milwaukee Oak Lawn Bloomington Cedar Rapids East Chicago Appleton Decatur Champaign Michigan City Green Bay Waterloo South Bend Rochester Holland Elkhart Jenison Wyoming Grand Rapids Kalamazoo Ankeny Des Moines Anderson Fort Wayne Muncie Fort Dodge Mankato Lansing Lima Blue Island Evergreen Park Skokie Evanston Dolton Muscatine Naperville Elmwood Park Joliet Franklin Park Chicago Aurora Iowa City Bridgeview Rockford Moline Calumet City Davenport Brookfield Middleton Oconomowoc Hammond Clinton 1 Mar 2 3 4 5 6 7 8 Every measured city in the area, coloured by its PM2.5 that day; a dark ring marks a city at twice its usual or more. Bars: cities counted each day, coloured by their median level. Choose a day or press play; without JavaScript, the days link to that day's world ranking.
How it spread
Brookfield Brookfield, 1 March: 2.5 µg/m³, 0.3× usual Brookfield, 2 March: 9.5 µg/m³, 1.3× usual Brookfield, 3 March: 21.5 µg/m³, 2.9× usual Brookfield, 4 March: 32.4 µg/m³, 4.3× usual Brookfield, 5 March: 28.2 µg/m³, 3.8× usual Brookfield, 6 March: 18.5 µg/m³, 2.5× usual Brookfield, 7 March: 4.9 µg/m³, 0.7× usual Brookfield, 8 March: 5.5 µg/m³, 0.7× usual Bridgeview Bridgeview, 1 March: 2.3 µg/m³, 0.3× usual Bridgeview, 2 March: 14.4 µg/m³, 1.8× usual Bridgeview, 3 March: 20.7 µg/m³, 2.6× usual Bridgeview, 4 March: 32.0 µg/m³, 4.0× usual Bridgeview, 5 March: 25.0 µg/m³, 3.1× usual Bridgeview, 6 March: 14.8 µg/m³, 1.9× usual Bridgeview, 7 March: 4.3 µg/m³, 0.5× usual Bridgeview, 8 March: 5.0 µg/m³, 0.6× usual Hammond Hammond, 1 March: 3.0 µg/m³, 0.5× usual Hammond, 2 March: 6.4 µg/m³, 1.0× usual Hammond, 3 March: 17.4 µg/m³, 2.7× usual Hammond, 4 March: 30.2 µg/m³, 4.7× usual Hammond, 5 March: 26.6 µg/m³, 4.2× usual Hammond, 6 March: 12.8 µg/m³, 2.0× usual Hammond, 7 March: 4.3 µg/m³, 0.7× usual Hammond, 8 March: 4.4 µg/m³, 0.7× usual Calumet City Calumet City, 1 March: 3.0 µg/m³, 0.4× usual Calumet City, 2 March: 6.5 µg/m³, 0.9× usual Calumet City, 3 March: 16.9 µg/m³, 2.4× usual Calumet City, 4 March: 28.6 µg/m³, 4.1× usual Calumet City, 5 March: 27.9 µg/m³, 4.0× usual Calumet City, 6 March: 14.0 µg/m³, 2.0× usual Calumet City, 7 March: 4.7 µg/m³, 0.7× usual Calumet City, 8 March: 4.4 µg/m³, 0.6× usual Franklin Park Franklin Park, 1 March: 2.5 µg/m³, 0.3× usual Franklin Park, 2 March: 7.2 µg/m³, 1.0× usual Franklin Park, 3 March: 20.3 µg/m³, 2.8× usual Franklin Park, 4 March: 28.2 µg/m³, 3.9× usual Franklin Park, 5 March: 20.8 µg/m³, 2.9× usual Franklin Park, 6 March: 14.0 µg/m³, 1.9× usual Franklin Park, 7 March: 4.6 µg/m³, 0.6× usual Franklin Park, 8 March: 5.5 µg/m³, 0.8× usual Skokie Skokie, 1 March: 4.5 µg/m³, 0.4× usual Skokie, 2 March: 7.6 µg/m³, 0.7× usual Skokie, 3 March: 18.8 µg/m³, 1.7× usual Skokie, 4 March: 28.2 µg/m³, 2.6× usual Skokie, 5 March: no reading Skokie, 6 March: 14.8 µg/m³, 1.4× usual Skokie, 7 March: 5.8 µg/m³, 0.5× usual Skokie, 8 March: 7.7 µg/m³, 0.7× usual Oconomowoc Oconomowoc, 1 March: 3.4 µg/m³, 0.6× usual Oconomowoc, 2 March: 4.4 µg/m³, 0.7× usual Oconomowoc, 3 March: 15.1 µg/m³, 2.5× usual Oconomowoc, 4 March: 28.0 µg/m³, 4.7× usual Oconomowoc, 5 March: 24.6 µg/m³, 4.1× usual Oconomowoc, 6 March: 11.5 µg/m³, 1.9× usual Oconomowoc, 7 March: 4.2 µg/m³, 0.7× usual Oconomowoc, 8 March: 6.3 µg/m³, 1.1× usual Evergreen Park Evergreen Park, 1 March: 4.2 µg/m³, 0.4× usual Evergreen Park, 2 March: 8.4 µg/m³, 0.8× usual Evergreen Park, 3 March: 22.1 µg/m³, 2.0× usual Evergreen Park, 4 March: 27.5 µg/m³, 2.5× usual Evergreen Park, 5 March: no reading Evergreen Park, 6 March: 15.0 µg/m³, 1.4× usual Evergreen Park, 7 March: 5.6 µg/m³, 0.5× usual Evergreen Park, 8 March: 7.1 µg/m³, 0.7× usual Chicago Chicago, 1 March: 2.4 µg/m³, 0.3× usual Chicago, 2 March: 7.4 µg/m³, 1.1× usual Chicago, 3 March: 18.5 µg/m³, 2.6× usual Chicago, 4 March: 27.4 µg/m³, 3.9× usual Chicago, 5 March: 20.9 µg/m³, 3.0× usual Chicago, 6 March: 14.0 µg/m³, 2.0× usual Chicago, 7 March: 4.8 µg/m³, 0.7× usual Chicago, 8 March: 5.6 µg/m³, 0.8× usual Elmwood Park Elmwood Park, 1 March: 2.3 µg/m³, 0.3× usual Elmwood Park, 2 March: 6.4 µg/m³, 0.8× usual Elmwood Park, 3 March: 18.8 µg/m³, 2.5× usual Elmwood Park, 4 March: 27.3 µg/m³, 3.6× usual Elmwood Park, 5 March: 17.9 µg/m³, 2.4× usual Elmwood Park, 6 March: 11.3 µg/m³, 1.5× usual Elmwood Park, 7 March: 4.6 µg/m³, 0.6× usual Elmwood Park, 8 March: 5.5 µg/m³, 0.7× usual Blue Island Blue Island, 1 March: 4.2 µg/m³, 0.4× usual Blue Island, 2 March: 8.2 µg/m³, 0.7× usual Blue Island, 3 March: 20.7 µg/m³, 1.8× usual Blue Island, 4 March: 26.9 µg/m³, 2.4× usual Blue Island, 5 March: no reading Blue Island, 6 March: 14.8 µg/m³, 1.3× usual Blue Island, 7 March: 5.7 µg/m³, 0.5× usual Blue Island, 8 March: 7.1 µg/m³, 0.6× usual Joliet Joliet, 1 March: 2.5 µg/m³, 0.4× usual Joliet, 2 March: 9.0 µg/m³, 1.3× usual Joliet, 3 March: 17.9 µg/m³, 2.6× usual Joliet, 4 March: 26.8 µg/m³, 3.8× usual Joliet, 5 March: 20.7 µg/m³, 3.0× usual Joliet, 6 March: 10.8 µg/m³, 1.5× usual Joliet, 7 March: 4.2 µg/m³, 0.6× usual Joliet, 8 March: 4.6 µg/m³, 0.7× usual Dolton Dolton, 1 March: 2.4 µg/m³, 0.3× usual Dolton, 2 March: 7.1 µg/m³, 0.8× usual Dolton, 3 March: 20.1 µg/m³, 2.4× usual Dolton, 4 March: 26.8 µg/m³, 3.2× usual Dolton, 5 March: 18.5 µg/m³, 2.2× usual Dolton, 6 March: 11.5 µg/m³, 1.4× usual Dolton, 7 March: 5.6 µg/m³, 0.7× usual Dolton, 8 March: 5.9 µg/m³, 0.7× usual Aurora Aurora, 1 March: 2.9 µg/m³, 0.4× usual Aurora, 2 March: 7.2 µg/m³, 1.1× usual Aurora, 3 March: 16.3 µg/m³, 2.5× usual Aurora, 4 March: 26.0 µg/m³, 3.9× usual Aurora, 5 March: 24.3 µg/m³, 3.7× usual Aurora, 6 March: 11.9 µg/m³, 1.8× usual Aurora, 7 March: 3.9 µg/m³, 0.6× usual Aurora, 8 March: 5.0 µg/m³, 0.8× usual Muscatine Muscatine, 1 March: no reading Muscatine, 2 March: 8.3 µg/m³, 1.1× usual Muscatine, 3 March: 15.3 µg/m³, 2.0× usual Muscatine, 4 March: 25.8 µg/m³, 3.3× usual Muscatine, 5 March: 20.9 µg/m³, 2.7× usual Muscatine, 6 March: 7.9 µg/m³, 1.0× usual Muscatine, 7 March: 5.2 µg/m³, 0.7× usual Muscatine, 8 March: 6.1 µg/m³, 0.8× usual Naperville Naperville, 1 March: 3.1 µg/m³, 0.4× usual Naperville, 2 March: 8.0 µg/m³, 1.1× usual Naperville, 3 March: 16.2 µg/m³, 2.3× usual Naperville, 4 March: 25.7 µg/m³, 3.6× usual Naperville, 5 March: 22.7 µg/m³, 3.2× usual Naperville, 6 March: 12.0 µg/m³, 1.7× usual Naperville, 7 March: 3.8 µg/m³, 0.5× usual Naperville, 8 March: 4.7 µg/m³, 0.7× usual Evanston Evanston, 1 March: 4.2 µg/m³, 0.4× usual Evanston, 2 March: 7.3 µg/m³, 0.8× usual Evanston, 3 March: 17.7 µg/m³, 1.8× usual Evanston, 4 March: 25.1 µg/m³, 2.6× usual Evanston, 5 March: 21.9 µg/m³, 2.3× usual Evanston, 6 March: 14.6 µg/m³, 1.5× usual Evanston, 7 March: 5.6 µg/m³, 0.6× usual Evanston, 8 March: 7.7 µg/m³, 0.8× usual Clinton Clinton, 1 March: 4.4 µg/m³, 0.7× usual Clinton, 2 March: 6.6 µg/m³, 1.0× usual Clinton, 3 March: 21.8 µg/m³, 3.3× usual Clinton, 4 March: 19.5 µg/m³, 3.0× usual Clinton, 5 March: 31.5 µg/m³, 4.8× usual Clinton, 6 March: 7.5 µg/m³, 1.1× usual Clinton, 7 March: 4.4 µg/m³, 0.7× usual Clinton, 8 March: 5.5 µg/m³, 0.8× usual Middleton Middleton, 1 March: 0.6 µg/m³, 0.1× usual Middleton, 2 March: 2.1 µg/m³, 0.3× usual Middleton, 3 March: 9.8 µg/m³, 1.6× usual Middleton, 4 March: 23.2 µg/m³, 3.7× usual Middleton, 5 March: 27.6 µg/m³, 4.4× usual Middleton, 6 March: 8.7 µg/m³, 1.4× usual Middleton, 7 March: 0.3 µg/m³, 0.0× usual Middleton, 8 March: 1.6 µg/m³, 0.3× usual Iowa City Iowa City, 1 March: 4.8 µg/m³, 0.7× usual Iowa City, 2 March: 7.6 µg/m³, 1.1× usual Iowa City, 3 March: 15.3 µg/m³, 2.3× usual Iowa City, 4 March: 23.9 µg/m³, 3.6× usual Iowa City, 5 March: 27.1 µg/m³, 4.0× usual Iowa City, 6 March: 8.5 µg/m³, 1.3× usual Iowa City, 7 March: 5.5 µg/m³, 0.8× usual Iowa City, 8 March: 7.0 µg/m³, 1.0× usual Davenport Davenport, 1 March: 4.2 µg/m³, 0.7× usual Davenport, 2 March: 5.3 µg/m³, 0.8× usual Davenport, 3 March: 16.5 µg/m³, 2.6× usual Davenport, 4 March: 24.5 µg/m³, 3.8× usual Davenport, 5 March: 27.0 µg/m³, 4.2× usual Davenport, 6 March: 6.5 µg/m³, 1.0× usual Davenport, 7 March: 4.0 µg/m³, 0.6× usual Davenport, 8 March: 5.0 µg/m³, 0.8× usual Moline Moline, 1 March: 4.5 µg/m³, 0.7× usual Moline, 2 March: 5.5 µg/m³, 0.9× usual Moline, 3 March: 18.4 µg/m³, 2.9× usual Moline, 4 March: 23.8 µg/m³, 3.8× usual Moline, 5 March: 26.0 µg/m³, 4.1× usual Moline, 6 March: 6.3 µg/m³, 1.0× usual Moline, 7 March: 4.2 µg/m³, 0.7× usual Moline, 8 March: 5.2 µg/m³, 0.8× usual Rockford Rockford, 1 March: 4.2 µg/m³, 0.7× usual Rockford, 2 March: 8.4 µg/m³, 1.4× usual Rockford, 3 March: 17.3 µg/m³, 2.8× usual Rockford, 4 March: 19.4 µg/m³, 3.1× usual Rockford, 5 March: 25.7 µg/m³, 4.1× usual Rockford, 6 March: 10.1 µg/m³, 1.6× usual Rockford, 7 March: 3.8 µg/m³, 0.6× usual Rockford, 8 March: 5.4 µg/m³, 0.9× usual 1 Mar 2 3 4 5 6 7 8 Every counted city, in the order the episode reached them, 3 days before to 3 after. Each square is a day, coloured by that day's PM2.5; outlined: at twice the city's usual or more. Good 0–50
Moderate 51–100
Sensitive groups 101–150
Unhealthy 151–200
Very unhealthy 201–300
Hazardous 301+
Every city it reached
City Days Highest Usual Above usual
Clinton Iowa, United States 1 5 March 6.6 4.8× Hammond Indiana, United States 2 4 March 6.4 4.7× Oconomowoc Wisconsin, United States 1 4 March 6.0 4.7× Middleton Wisconsin, United States 1 5 March 6.3 4.4× Brookfield Illinois, United States 2 4 March 7.5 4.3× Davenport Iowa, United States 1 5 March 6.4 4.2× Rockford Illinois, United States 1 5 March 6.2 4.1× Moline Illinois, United States 1 5 March 6.3 4.1× Calumet City Illinois, United States 2 4 March 7.0 4.1× Iowa City Iowa, United States 1 5 March 6.7 4.0× Bridgeview Illinois, United States 2 4 March 8.0 4.0× Aurora Illinois, United States 1 4 March 6.6 3.9× Franklin Park Illinois, United States 1 4 March 7.2 3.9× Chicago Illinois, United States 1 4 March 7.0 3.9× Joliet Illinois, United States 1 4 March 7.0 3.8× Elmwood Park Illinois, United States 1 4 March 7.6 3.6× Naperville Illinois, United States 1 4 March 7.2 3.6× Muscatine Iowa, United States 1 4 March 7.8 3.3× Dolton Illinois, United States 1 4 March 8.4 3.2× Evanston Illinois, United States 1 4 March 9.6 2.6× Skokie Illinois, United States 1 4 March 10.9 2.6× Evergreen Park Illinois, United States 1 4 March 10.8 2.5× Blue Island Illinois, United States 1 4 March 11.2 2.4×
Daily means in µg/m³. Usual: the city's median for this time of year (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that.
Against other episodes in the United States
Number 37 of 98 episodes in the United States since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 279 North-eastern United States and Canada, July 2026 264 North-eastern United States and Canada, May and June 2023 260 North-eastern United States and Canada, July and August 2025 241 North-eastern United States and Canada, July 2023 241 North-eastern United States and Canada, June 2025 196 North-eastern United States and Canada, June 2023 161 North-eastern United States and Canada, July 2025 119 North-western United States and Canada, August 2023 110 North-eastern United States, June 2025 104 North-western United States and Canada, August 2026 99 North-eastern United States and Canada, February 2026 96 Illinois and Iowa, United States, March 2026 23 Bars: cities reached; colour: the level of the episode's highest daily reading. All 98 .
Use this page SmogRank, Illinois and Iowa, United States, March 2026: 23 cities with PM2.5 at twice their usual or more, 4 to 5 March 2026, smogrank.com/episodes/2026-03-illinois-and-iowa-united-states (accessed 2 October 2026).
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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms .
An episode is a run of days when many cities close to each other (four or more within 350 km on a day, 8 or more in all) each had a daily PM2.5 mean of at least 25 µg/m³ and at least 2 times their usual for that time of year. Found in our own measurements, not picked by hand. How we find episodes . Values are each city's daily mean of its own monitors; causes are the usual kinds for a pattern like this, not a confirmed source.
