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

Air over Downtown Los Angeles. Photo courtesy of David17 & Pixabay.com.

2008 and 2016

Number of UNHEALTHY AIR DAYS in Descending Order, 2016:

 
County Number of Days with Air Quality Index Data Number of Days When Air Quality Was:
Good Moderate Unhealthy for Sensitive Groups Unhealthy or Very Unhealthy
Hawaii County, HI 366 1 53 124 188
San Bernardino County, CA 366 26 191 78 71
Riverside County, CA 366 44 194 85 43
Fresno County, CA 366 88 165 77 36
Gila County, AZ 366 81 133 117 35
Tulare County, CA 366 76 155 102 33
Mono County, CA 366 314 19 3 30
Kern County, CA 366 65 175 101 25
Los Angeles County, CA 366 32 230 81 23
El Dorado County, CA 244 120 83 20 21
Inyo County, CA 366 236 97 15 18
Fairbanks North Star Borough, AK 366 237 92 22 15
Maricopa County, AZ 366 59 260 35 12
San Benito County, CA 366 294 56 5 11
Shasta County, CA 366 287 54 14 11

Number of UNHEALTHY AIR DAYS in Descending Order, 2008:

County Number of Days with Air Quality Index Data Number of Days When Air Quality Was:
Good Moderate Unhealthy for Sensitive Groups Unhealthy or Very Unhealthy
Pinal County, AZ 366 70 112 100 84
San Bernardino County, CA 305 100 87 70 48
Riverside County, CA 366 114 140 75 37
Los Angeles County, CA 250 71 108 43 28
Kern County, CA 278 51 134 67 26
Tulare County, CA 305 110 87 84 24
Hawaii County, HI 305 52 195 42 16
Fresno County, CA 281 80 130 56 15
Kings County, CA 305 89 169 38 9
San Diego County, CA 308 124 151 29 4
Harris County, TX 306 128 157 19 2
Maricopa County, AZ 366 100 233 32 1
Allegheny County, PA 306 119 153 33 1
Douglas County, NE 275 66 206 3 0
Jefferson County, AL 336 118 202 16 0

Good - Percent of days in the year when air quality rated "good" on the PSI scale. Calculated as 100 * (days with PSI values 0 through 50) / (total days with PSI values).
Moderate - Percent of days in the year when air quality rated "moderate" on the PSI scale. Calculated as 100 * (days with PSI values 51 through 100) / (total days with PSI values).
Unhealthful - Percent of days in the year when air quality rated "unhealthful" (or worse) on the PSI scale. Calculated as 100* (days with PSI values above 100) / (total days with PSI values).

A PSI (Pollutant Standards Index) value is an approximate indicator of overall air quality, because it takes into account all of the pollutants measured within a county. Many counties have monitoring stations for some, but not all, of the pollutants. PSI values reflect all of the available measurements in each county.

Source: U.S. Environmental Protection Agency