Is the Air Getting
Better or Worse?
10 years of EPA monitoring data for every major U.S. city. Annual AQI averages, unhealthy air days, pollutant breakdowns, and a proprietary A-F Air Quality Grade — so you can see whether the air where you live is improving or declining.
Popular Cities
Air quality trends for the most-searched US cities
Cleanest Air in America
Top 10 cities by Air Quality Grade
#1Caguas, Puerto Rico
Primary pollutant: NO2
#2Alexandria City, Virginia
Primary pollutant: PM10
#3Cook, Minnesota
Primary pollutant: PM2.5
#4San Juan, Puerto Rico
Primary pollutant: CO
#5Carbon, Wyoming
Primary pollutant: Ozone
#6Monroe, Michigan
Primary pollutant: PM10
#7Juncos, Puerto Rico
Primary pollutant: Ozone
#8Matanuska-Susitna, Alaska
Primary pollutant: PM2.5
#9Uinta, Wyoming
Primary pollutant: Ozone
#10Adjuntas, Puerto Rico
Primary pollutant: PM2.5
Worst Air Quality in America
Bottom 10 cities by Air Quality Grade
#1Maricopa, Arizona
Primary pollutant: Ozone
#2BAJA CALIFORNIA NORTE, Country Of Mexico
Primary pollutant: PM2.5
#3Inyo, California
Primary pollutant: Ozone
#4San Bernardino, California
Primary pollutant: Ozone
#5Los Angeles, California
Primary pollutant: PM2.5
#6Riverside, California
Primary pollutant: Ozone
#7San Diego, California
Primary pollutant: PM2.5
#8Plumas, California
Primary pollutant: PM2.5
#9Tulare, California
Primary pollutant: Ozone
#10Harris, Texas
Primary pollutant: PM2.5
Fastest-Improving Air Quality
Cities with the steepest downward AQI trends
#1Hawaii, Hawaii
Primary pollutant: PM2.5
#2Carbon, Wyoming
Primary pollutant: Ozone
#3Uinta, Wyoming
Primary pollutant: Ozone
#4Rosebud, Montana
Primary pollutant: Ozone
#5St Croix, Virgin Islands
Primary pollutant: PM2.5
#6Monroe, Michigan
Primary pollutant: PM10
Air Quality Research
Data-driven analysis powered by EPA monitoring data
Best Cities for People with Asthma
Ranked by unhealthy air days and pollutant type
ClimateHow Wildfires Changed Air Quality
Smoke has reversed decades of progress in the West
GuideIs It Safe to Run Outside?
AQI thresholds and best times for outdoor exercise
AnalysisCOVID Lockdowns & Air Quality
Did lockdowns improve air? Did it last?
PollutantPM2.5 Trends by City
Fine particulate matter — the deadliest pollutant
PollutantOzone (Smog) Trends
Ground-level ozone and climate change
Browse by State
54 states and territories with EPA monitoring data
California
53 monitored areas
Texas
42 monitored areas
Ohio
40 monitored areas
Pennsylvania
40 monitored areas
Florida
39 monitored areas
North Carolina
37 monitored areas
Indiana
36 monitored areas
Colorado
32 monitored areas
Virginia
32 monitored areas
Washington
30 monitored areas
New York
29 monitored areas
Georgia
29 monitored areas
Michigan
28 monitored areas
Wisconsin
27 monitored areas
Kentucky
27 monitored areas
Illinois
23 monitored areas
Tennessee
23 monitored areas
Oregon
23 monitored areas
Oklahoma
22 monitored areas
Louisiana
22 monitored areas
Missouri
21 monitored areas
Minnesota
21 monitored areas
Idaho
20 monitored areas
Montana
19 monitored areas
South Carolina
18 monitored areas
Wyoming
18 monitored areas
Alabama
17 monitored areas
Maryland
16 monitored areas
New Jersey
16 monitored areas
New Mexico
16 monitored areas
Iowa
16 monitored areas
Utah
15 monitored areas
West Virginia
14 monitored areas
Arizona
13 monitored areas
Massachusetts
13 monitored areas
Puerto Rico
11 monitored areas
Arkansas
11 monitored areas
Kansas
11 monitored areas
Maine
10 monitored areas
North Dakota
10 monitored areas
Mississippi
10 monitored areas
South Dakota
10 monitored areas
Nevada
9 monitored areas
Nebraska
9 monitored areas
Alaska
8 monitored areas
Connecticut
8 monitored areas
New Hampshire
7 monitored areas
Vermont
4 monitored areas
Hawaii
4 monitored areas
Delaware
3 monitored areas
Rhode Island
3 monitored areas
Country Of Mexico
2 monitored areas
Virgin Islands
2 monitored areas
District Of Columbia
1 monitored areas
Frequently Asked Questions
What is an Air Quality Grade?
The Air Quality Grade is AirHistory's scoring system that rates cities from A (cleanest) to F (most polluted) based on four factors: 5-year average AQI (40%), whether air quality is improving or worsening (30%), number of unhealthy days per year (20%), and the dominant pollutant type (10%).
Where does this data come from?
All data comes from the EPA's Air Quality System (AQS), which collects ambient air quality data from monitoring stations across the country. We use the annual AQI by county dataset, which covers 2014 through 2023 — a full decade of air quality measurements.
What is AQI?
The Air Quality Index (AQI) is the EPA's standardized measure for reporting air quality. An AQI of 0-50 is "Good," 51-100 is "Moderate," and above 100 is progressively unhealthy. AQI accounts for five major pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide.
Why trends matter more than today's reading
Real-time AQI can swing wildly due to weather, wildfires, or seasonal changes. The 10-year trend tells you whether a city's air quality is fundamentally improving or declining — a much better signal for health decisions and relocation planning.
What is a moderate AQI level of concern?
An AQI between 51-100 is classified as "Moderate" by the EPA. Air quality is acceptable, but some pollutants may be a concern for a very small number of people who are unusually sensitive to air pollution. Most people can exercise and go about daily activities normally at moderate AQI levels.
Which cities have the worst air pollution in the US?
Based on 10-year EPA data, cities in California's Central Valley (Fresno, Bakersfield, Visalia) consistently have the worst air quality, driven by wildfire smoke, agricultural emissions, and geography that traps pollutants. Check each city's full AQI history and grade on AirHistory.