Bad Air Days in San Miguel County, Colorado: under 1 a Year

under 1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 724 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (0% particle days).

Which months to watch

Most bad days here fall in June and August. Averaged over 2016 to 2025.

Is a purifier worth it here?

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

Better or worse than it was

The worst recent year was 2018, with 2 bad days on 238 monitored days.

Date	AQI	Main pollutant
2020-08-21	136	Ozone
2020-08-22	119	Ozone
2022-06-15	108	Ozone
2016-06-15	105	Ozone
2018-06-11	101	Ozone

Most days, not the worst ones

Across 2,686 monitored days from 2016 to 2025, the air in San Miguel County rated Good on 76% of them, more often than the 72% typical of monitored counties, and Moderate on 24%. The median day sat at AQI 41; one day in ten went above 62.

The pollutant setting the AQI on an ordinary day here:

ozone67%1,787 days
coarse dust (PM10)28%739 days
fine particles (PM2.5)6%160 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	303	62	0	0	36	94
2024	361	311	50	0	0	19	97
2023	253	185	68	0	0	47	84
2022	255	194	60	1	0	45	108
2021	252	165	87	0	0	48	97
2020	247	155	90	2	0	48	136
2019	241	189	52	0	0	45	87
2018	238	160	76	2	0	46	101
2017	229	197	32	0	0	43	87
2016	245	189	55	1	0	44	105
2015	236	188	47	1	0	44	105
2014	274	205	69	0	0	45	93
2013	262	173	87	2	1	47	156
2012	209	163	45	1	0	44	119
2011	246	142	102	2	0	48	101
2010	147	129	17	1	1	19	200

*2025 may be a partial year in EPA's file.

Nearby counties on file

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.