Air Quality in Colorado

Colorado has 34 counties with EPA air quality monitoring. Air quality is generally worsening across the state, with an average of 220 "Good" days per county per year. The best air quality is in San Juan (median AQI 9) and the most polluted is Teller (median AQI 58).

County	Median AQI	Max AQI	Good Days	Unhealthy Days	Trend	Top Pollutant
Adams	55	161	147	22	→ stable	Ozone
Alamosa	26	98	325	0	→ stable	PM2.5
Arapahoe	49	161	196	17	→ stable	Ozone
Archuleta	32	80	349	0	↑ worsening	Ozone
Boulder	49	154	212	10	→ stable	Ozone
Chaffee	51	112	74	5	↑ worsening	Ozone
Clear Creek	49	136	202	10	→ stable	Ozone
Delta	44	80	125	0	↑ worsening	Ozone
Denver	55	172	129	29	→ stable	Ozone
Douglas	48	166	208	25	→ stable	Ozone
El Paso	49	166	202	14	→ stable	Ozone
Fremont	13	59	354	0	→ stable	PM10
Garfield	49	133	216	5	→ stable	Ozone
Gilpin	48	150	240	12	→ stable	Ozone
Grand	45	93	133	0	→ stable	Ozone
Gunnison	47	100	243	0	→ stable	Ozone
Jackson	44	105	304	3	↑ worsening	Ozone
Jefferson	50	174	192	37	→ stable	Ozone
La Plata	46	240	241	2	→ stable	Ozone
Larimer	54	161	156	23	→ stable	Ozone
Mesa	48	136	215	7	→ stable	Ozone
Moffat	42	108	262	1	↓ improving	Ozone
Montezuma	45	101	262	1	→ stable	Ozone
Montrose	42	122	257	1	↓ improving	Ozone
Park	50	147	172	12	→ stable	Ozone
Pitkin	19	76	246	0	↑ worsening	PM2.5
Prowers	25	98	321	0	↑ worsening	PM2.5
Pueblo	44	143	249	8	↑ worsening	Ozone
Rio Blanco	46	142	266	4	→ stable	Ozone
Routt	12	53	364	0	→ stable	PM10
San Juan	9	51	120	0	→ stable	PM2.5
San Miguel	19	97	311	0	→ stable	PM10
Teller	58	133	63	12	↓ improving	Ozone
Weld	54	164	149	21	→ stable	Ozone