Published April 6, 2026 · Updated monthly
PM2.5 Trends: Which Cities Are Getting Worse?
PM2.5 is the dominant pollutant in 531 US cities, and 30 of them are trending in the wrong direction. Fine particulate matter — the air pollutant most strongly linked to premature death — is rising in dozens of communities, driven primarily by wildfire smoke in the West and persistent industrial emissions in parts of the East.
Cities With Rising PM2.5 Levels
These cities show the steepest upward PM2.5-driven AQI trends over 10 years of EPA monitoring (2014-2023). 12 are in western states where wildfire smoke is the primary driver. 18 are in eastern or central states where industrial emissions, traffic, and transported smoke contribute.
| Rank | City | State | Current AQI | 5yr Avg AQI | Grade | Trend |
|---|---|---|---|---|---|---|
| 1 | Catano, Puerto Rico | PR | 52 | 42 | D | +3.3/yr |
| 2 | Sanders, Montana | MT | 37 | 36 | D | +3.0/yr |
| 3 | Valley, Idaho | ID | 36 | 37 | D | +2.8/yr |
| 4 | Cass, Minnesota | MN | 32 | 32 | C | +2.3/yr |
| 5 | Grant, Oklahoma | OK | 32 | 28 | C | +2.2/yr |
| 6 | Columbia, Washington | WA | 39 | 32 | C | +2.2/yr |
| 7 | Douglas, Oregon | OR | 53 | 36 | C | +2.1/yr |
| 8 | Codington, South Dakota | SD | 45 | 40 | D | +1.9/yr |
| 9 | Mono, California | CA | 24 | 33 | D | +1.9/yr |
| 10 | Rock Island, Illinois | IL | 51 | 47 | D | +1.9/yr |
| 11 | Jackson, Mississippi | MS | 51 | 46 | D | +1.8/yr |
| 12 | Bonner, Idaho | ID | 34 | 33 | C | +1.8/yr |
| 13 | Culberson, Texas | TX | 20 | 37 | C | +1.7/yr |
| 14 | Asotin, Washington | WA | 49 | 43 | D | +1.6/yr |
| 15 | Del Norte, California | CA | 32 | 32 | C | +1.6/yr |
| 16 | Sangamon, Illinois | IL | 51 | 46 | D | +1.6/yr |
| 17 | Canyon, Idaho | ID | 34 | 41 | C | +1.6/yr |
| 18 | BAJA CALIFORNIA NORTE, Country Of Mexico | MX | 66 | 81 | F | +1.6/yr |
| 19 | Henderson, Kentucky | KY | 53 | 53 | D | +1.5/yr |
| 20 | Bolivar, Mississippi | MS | 52 | 47 | C | +1.4/yr |
| 21 | McLean, Illinois | IL | 50 | 48 | D | +1.4/yr |
| 22 | Blaine, Idaho | ID | 19 | 21 | C | +1.4/yr |
| 23 | Harney, Oregon | OR | 43 | 44 | C | +1.3/yr |
| 24 | Lafourche, Louisiana | LA | 53 | 48 | C | +1.3/yr |
| 25 | DuPage, Illinois | IL | 53 | 49 | D | +1.3/yr |
Why PM2.5 Is Different From Other Pollutants
PM2.5 particles are small enough (2.5 micrometers or less) to bypass the body's natural defenses. They pass through your nose and throat, penetrate deep into the lungs, and enter the bloodstream. The World Health Organization considers PM2.5 the air pollutant most harmful to human health, linked to:
- Heart attacks and stroke
- Lung cancer
- Chronic respiratory disease
- Premature death — the EPA estimates tens of thousands of US deaths annually are attributable to PM2.5 exposure
The Wildfire Connection
The majority of cities with rising PM2.5 are in the western US, where wildfire smoke has become the dominant source of fine particulate matter. Unlike vehicle or industrial emissions — which have been declining for decades — wildfire emissions are increasing as climate change extends fire seasons and intensifies burns.
The EPA's most recent PM2.5 trend analysis shows that if wildfire-influenced days are excluded, national PM2.5 levels are at historic lows. But those wildfire days are becoming more frequent, longer, and more intense — making the exclusion increasingly academic.
What This Means for Your Health
If you live in a city where PM2.5 is trending upward:
- Monitor daily AQI — check AirNow or your city page on AirHistory before outdoor activity
- Invest in HEPA filtration — a portable HEPA air purifier in your bedroom and living room can reduce indoor PM2.5 by 65-90%
- Time outdoor activity — PM2.5 levels are often lowest in early morning before traffic builds and wildfire smoke descends
- Talk to your doctor if you have heart or lung conditions — ask about adjusting medications during high-PM2.5 periods
Frequently Asked Questions
Cities in California's Central Valley (Fresno, Bakersfield), wildfire-prone areas of the Pacific Northwest, and some industrial cities in the Midwest consistently have the highest PM2.5 levels. See the full ranking table above for the cities with the steepest worsening trends.
The WHO considers PM2.5 the air pollutant most harmful to human health globally. It is the strongest single environmental risk factor for premature death, linked to cardiovascular disease, lung cancer, and respiratory illness. Even short-term exposure during wildfire events carries measurable health risk.
At high concentrations, PM2.5 creates visible haze — the smoky or milky appearance of the sky during wildfire smoke events. At lower concentrations, PM2.5 is invisible. You cannot rely on visibility alone to assess PM2.5 risk; always check AQI readings from monitoring stations.
Reducing PM2.5 requires addressing its sources: transitioning from fossil fuels to renewables, electrifying vehicles, controlling industrial emissions, and managing wildfire risk through prescribed burns and forest thinning. For individuals, HEPA air purifiers and N95 masks during smoke events are the most effective protections.
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