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U.S. Counties with Highest Number of Unhealthy Air Quality Days

Air Quality Over Los Angeles

Smoggy versus clean air over Downtown Los Angeles. Undated photos. From The History of the California Environmental Protection Agency, courtesy of the California Environmental Protection Agency.


Also see: Annual Air Quality Days by Year - Los Angeles County



As measured over 365 days. Counties ordered by UNHEALTHY AIR DAYS in descending order, 2019.

County Number of Days When Air Quality Was:
Good Moderate Unhealthy for Sensitive Groups Unhealthy Very Unhealthy or Hazardous
New Madrid, MO 49 50 145 121 0
San Bernardino County, CA 55 177 71 54 8
Riverside County, CA 75 170 91 29 0
LOS ANGELES COUNTY, CA 66 213 57 28 1
Fairbanks North Star Borough, AK 238 97 12 14 4
Kern County, CA 119 151 87 6 2
Gila County, AZ 145 164 50 6 0
Mariposa County, CA 221 130 9 5 0
Allegheny County, PA 138 212 11 4 0
County Number of Days When Air Quality Was:
Good Moderate Unhealthy for Sensitive Groups Unhealthy Very Unhealthy or Hazardous
Harris County, TX 179 159 22 4 1
Uintah County, UT 223 125 12 4 1
Duchesne County, UT 234 120 7 4 0
Jackson County, OR 295 63 3 4 0
Anchorage Borough, AK 289 67 5 4 0
Dona Ana County, NM 170 171 17 3 4
Sublette County, WY 266 88 8 3 0
Fairfield County, CT 262 82 18 3 0
Navarro County, TX 275 80 7 3 0

Good Quality Air Days - Number of days in the year when the Air Quality Index (AQI) value is 0 through 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
Moderate Quality Air Days - Number of days in the year when the Air Quality Index (AQI) value is 51 through 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
Unhealthy for Sensitive Groups - Number of days in the year when the Air Quality Index (AQI) value is 100 through 150. Members of sensitive groups may experience health effects. The general public is not likely to be affected.
Unhealthy Air Days - Number of days in the year when the Air Quality Index (AQI) value is 151 through 150. Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
Very Unhealthy Air Days - Number of days in the year when the Air Quality Index (AQI) value is 201 or higher.Health alert: everyone may experience more serious health effects. When the AQI exceeds 300, the air situation is considered hazardous, meriting a health emergency. The entire population is more likely to be affected.

Source: U.S. Environmental Protection Agency