Air quality by state

Every state ranked by how many bad-air days its monitored counties had from 2021 to 2025. Arizona is highest, at about 67 a year, or 1 day in 5. In 4 states the average is under 1 a year.

Worst counties in the US Cleanest counties in the US

#
1	Arizona13 counties with monitors	67
2	California52 counties with monitors	53
3	Nevada9 counties with monitors	25
4	Texas44 counties with monitors	18
5	Utah14 counties with monitors	16
6	Colorado24 counties with monitors	15
7	New Mexico11 counties with monitors	15
8	Illinois23 counties with monitors	13
9	Connecticut8 counties with monitors	11
10	North Dakota9 counties with monitors	10
11	Idaho19 counties with monitors	7.5
12	Wisconsin29 counties with monitors	7.4
13	Oklahoma19 counties with monitors	6.6
14	Michigan25 counties with monitors	6.6
15	Alaska5 counties with monitors	6.4
16	District of Columbia1 county with monitors	6.4
17	Oregon21 counties with monitors	6.0
18	Montana19 counties with monitors	5.9
19	Minnesota20 counties with monitors	5.8
20	South Dakota10 counties with monitors	5.7
21	Indiana32 counties with monitors	5.1
22	Pennsylvania38 counties with monitors	4.7
23	Ohio36 counties with monitors	4.6
24	Missouri19 counties with monitors	4.6
25	Washington29 counties with monitors	4.5
26	Kentucky25 counties with monitors	4.3
27	Wyoming18 counties with monitors	4.1
28	New York27 counties with monitors	4.0
29	New Jersey15 counties with monitors	3.8
30	Kansas10 counties with monitors	3.8
31	Iowa12 counties with monitors	3.8
32	Nebraska9 counties with monitors	3.5
33	Delaware3 counties with monitors	3.2
34	Maryland16 counties with monitors	3.1
35	Tennessee23 counties with monitors	2.9
36	Arkansas6 counties with monitors	2.8
37	Georgia26 counties with monitors	2.5
38	Rhode Island3 counties with monitors	2.2
39	Alabama14 counties with monitors	1.9
40	Massachusetts13 counties with monitors	1.9
41	Vermont3 counties with monitors	1.8
42	Louisiana19 counties with monitors	1.7
43	Maine11 counties with monitors	1.5
44	New Hampshire7 counties with monitors	1.5
45	Virginia25 counties with monitors	1.5
46	Mississippi10 counties with monitors	1.3
47	North Carolina34 counties with monitors	1.2
48	Florida38 counties with monitors	0.9
49	South Carolina13 counties with monitors	0.7
50	West Virginia11 counties with monitors	0.6
51	Hawaii3 counties with monitors	0.2

A state's number is the population-weighted average of its counties with monitors: days a year with an AQI over 100, when the EPA says children, older adults and people with asthma or heart or lung disease should cut back outdoors. Counties without monitors aren't in it. Use the column headings to sort.