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The U.S. Cities Hit Hardest by Wildfire Smoke in 2026
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Key Takeaways
- During the July 14–19 smoke wave, PM2.5 in Duluth, MN averaged 188.7 micrograms per cubic meter (µg/m³), more than 31 times its January–June baseline, peaking at a daily median of 507.8 µg/m³.
- 21 of the 25 hardest-hit U.S. metro areas averaged above 35.5 µg/m³, the level the EPA classifies as “Unhealthy for Sensitive Groups,” across the full six days.
- Much of the smoke came from eight fast-growing wildfires in northwestern Ontario, hundreds of miles from many of the hardest-hit cities.
In mid-July 2026, wildfire smoke turned air quality into a multi-state emergency across the U.S. Midwest and Northeast, including in many cities far from any active fire.
This graphic maps satellite-detected smoke coverage and active fire locations as of July 19, 2026, and ranks U.S. metro areas hit hardest by the rise in fine particulate matter (PM2.5), particles small enough to penetrate deep into the lungs and enter the bloodstream, during the July 14–19 smoke wave.
City readings come from the U.S. EPA’s AirNow monitoring network, with smoke coverage from NOAA’s Hazard Mapping System and active-fire locations from the National Interagency Fire Center and Canadian active-fire data.
Each metro area’s July 14–19 average of daily monitoring-site medians is compared with its January–June 2026 baseline, covering metro areas of at least 100,000 people.
The U.S. Cities Where Wildfire Smoke Worsened Air Quality the Most
No city took a bigger hit than Duluth, Minnesota. Its PM2.5 averaged 188.7 µg/m³ over the six-day window, up from a January–June baseline of just 6.0, and its worst day reached a daily median of 507.8 µg/m³, four times the EPA’s 125.5 µg/m³ “Very Unhealthy” threshold.
Conditions were severe enough that northeast Minnesota opened a clean-air shelter and distributed respirators as readings reached hazardous levels.
The table below shows all 25 metro areas ranked by the increase in their average daily PM2.5 during the smoke wave, along with each area’s single worst daily reading:
| Rank | Metro Area | State | Air Quality: PM2.5 (µg/m³) | |||
|---|---|---|---|---|---|---|
| Jan–June Baseline Avg. | July 14–19 Avg. | Change | Peak Daily Median | |||
| 1 | Duluth | MN | 6.0 | 188.7 | +182.7 | 507.8 |
| 2 | Toledo | OH | 8.7 | 109.5 | +100.8 | 367.8 |
| 3 | Detroit | MI | 7.5 | 106.5 | +99.0 | 295.6 |
| 4 | Grand Rapids | MI | 8.5 | 96.2 | +87.7 | 264.8 |
| 5 | Milwaukee | WI | 6.5 | 94.0 | +87.6 | 252.6 |
| 6 | Chicago | IL | 7.3 | 76.5 | +69.2 | 234.8 |
| 7 | Weirton-Steubenville | WV | 6.9 | 73.1 | +66.2 | 201.4 |
| 8 | Madison | WI | 6.2 | 69.9 | +63.7 | 180.4 |
| 9 | Youngstown | OH | 6.7 | 66.2 | +59.5 | 148.7 |
| 10 | Pittsburgh | PA | 6.7 | 63.4 | +56.8 | 160.4 |
| 11 | Harrisburg | PA | 8.3 | 64.8 | +56.5 | 148.4 |
| 12 | Lancaster | PA | 9.6 | 55.6 | +46.0 | 130.4 |
| 13 | Minneapolis-St. Paul | MN | 5.9 | 49.2 | +43.4 | 133.4 |
| 14 | Dover | DE | 7.4 | 50.1 | +42.8 | 138.9 |
| 15 | Philadelphia | PA | 7.8 | 50.1 | +42.3 | 121.5 |
| 16 | Columbus | OH | 7.4 | 44.6 | +37.2 | 155.2 |
| 17 | Trenton-Princeton | NJ | 6.5 | 41.6 | +35.0 | 88.2 |
| 18 | Baltimore | MD | 7.1 | 38.8 | +31.7 | 113.8 |
| 19 | Atlantic City | NJ | 5.7 | 36.9 | +31.2 | 82.3 |
| 20 | New York | NY | 7.1 | 37.4 | +30.2 | 72.9 |
| 21 | Washington | DC | 7.0 | 36.5 | +29.5 | 110.6 |
| 22 | Bridgeport-Stamford | CT | 6.8 | 35.2 | +28.4 | 69.2 |
| 23 | Spokane | WA | 4.6 | 29.9 | +25.4 | 116.4 |
| 24 | Hartford | CT | 7.0 | 28.2 | +21.2 | 50.8 |
| 25 | Richmond | VA | 7.0 | 27.7 | +20.7 | 102.2 |
The entire top 10 sits in the Great Lakes region and Ohio Valley, and every one of these metro areas averaged above the EPA’s 55.5 µg/m³ “Unhealthy” threshold, not for a single afternoon, but as their average across six straight days.
Even East Coast Cities Breathed Unhealthy Air for Days
By July 17, the smoke reached the Eastern Seaboard. New York averaged 37.4 µg/m³ across the six days, 5.2 times its baseline, while Washington, DC averaged 36.5, with both sitting above the 35.5 µg/m³ level that is unhealthy for sensitive groups.
In total, 21 of the 25 hardest-hit metro areas stayed above that threshold as a six-day average. That is a striking inversion of the best and worst U.S. states for air quality in normal times, when the highest long-term PM2.5 readings are typically found in California and the West.
The table below shows when each metro area’s air peaked during the wave, and how many of the six days its daily median was at or above the 35.5 µg/m³ threshold:
| Rank | Metro Area | State | Peak Date | Days ≥35.5 µg/m³ |
|---|---|---|---|---|
| 1 | Duluth | MN | Jul. 16 | 4 |
| 2 | Toledo | OH | Jul. 16 | 3 |
| 3 | Detroit | MI | Jul. 16 | 4 |
| 4 | Grand Rapids | MI | Jul. 16 | 4 |
| 5 | Milwaukee | WI | Jul. 16 | 5 |
| 6 | Chicago | IL | Jul. 16 | 3 |
| 7 | Weirton-Steubenville | WV | Jul. 17 | 4 |
| 8 | Madison | WI | Jul. 16 | 3 |
| 9 | Youngstown | OH | Jul. 17 | 3 |
| 10 | Pittsburgh | PA | Jul. 17 | 3 |
| 11 | Harrisburg | PA | Jul. 17 | 3 |
| 12 | Lancaster | PA | Jul. 17 | 3 |
| 13 | Minneapolis-St. Paul | MN | Jul. 16 | 3 |
| 14 | Dover | DE | Jul. 17 | 3 |
| 15 | Philadelphia | PA | Jul. 17 | 3 |
| 16 | Columbus | OH | Jul. 17 | 3 |
| 17 | Trenton-Princeton | NJ | Jul. 16 | 3 |
| 18 | Baltimore | MD | Jul. 17 | 3 |
| 19 | Atlantic City | NJ | Jul. 17 | 3 |
| 20 | New York | NY | Jul. 16 | 4 |
| 21 | Washington | DC | Jul. 17 | 2 |
| 22 | Bridgeport-Stamford | CT | Jul. 16 | 2 |
| 23 | Spokane | WA | Jul. 17 | 1 |
| 24 | Hartford | CT | Jul. 18 | 2 |
| 25 | Richmond | VA | Jul. 17 | 1 |
The peak-date column traces the plume’s eastward march: readings topped out around the western Great Lakes on July 16, across the Ohio Valley and mid-Atlantic on July 17, and in New England on July 18.
Eight Ontario Fires Sent Smoke Hundreds of Miles
Much of the smoke came from eight fast-growing wildfires in northwestern Ontario. As the plume spread south and east, the EPA issued a cross-border smoke statement on July 17, and states across the Midwest and East issued air-quality alerts.
Distance offered limited protection. Wind direction and plume height, not distance alone, determine which cities get the worst air, which is why the highest readings traced the plume’s path across the Great Lakes rather than simply hugging the border.
Spokane, WA, the only metro area west of the Rockies in the ranking, sat under smoke from separate fires in the West rather than the Ontario plume. And North America’s fires are part of a wider pattern this season: Europe is already nearing last year’s burned area as its own fire season accelerates.
Learn More on the Voronoi App
If you enjoyed today’s post, check out The Best and Worst U.S. States for Air Quality on Voronoi.