Bad Air Days in La Plata County, Colorado: 5 a Year

5 bad air days a year

More bad air days than three quarters of monitored counties. Ranked 227 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (48% particle days).

The bad-air season here

Most bad days here fall in June and July 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.

The worst days on file

In 2000 to 2009 this county averaged 3 bad days a year; in 2016 to 2025, 5. Not much has changed. The worst recent year was 2018, with 20 bad days on 365 monitored days.

Date	AQI	Main pollutant
2018-06-11	243	PM2.5
2024-04-24	240	PM2.5
2023-09-29	211	PM2.5
2018-06-09	208	PM2.5
2018-06-12	203	PM2.5

An ordinary day in La Plata

Across 3,652 monitored days from 2016 to 2025, the air in La Plata County rated Good on 68% of them, less often than the 72% typical of monitored counties, and Moderate on 31%. The median day sat at AQI 46; one day in ten went above 71.

The pollutant setting the AQI on an ordinary day here:

ozone91%3,318 days
fine particles (PM2.5)9%321 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	222	141	2	0	48	112
2024	366	242	122	2	1	46	240
2023	365	237	123	5	3	46	211
2022	365	266	98	1	0	46	108
2021	364	239	121	4	0	47	140
2020	366	273	91	2	0	45	133
2019	365	267	98	0	0	44	87
2018	365	236	109	20	10	45	243
2017	365	255	106	4	0	46	112
2016	366	238	120	8	0	47	122
2015	365	271	92	2	0	43	108
2014	365	279	85	1	0	44	101
2013	365	232	128	5	1	47	293
2012	366	218	146	2	0	48	108
2011	365	208	147	10	0	49	150
2010	365	220	135	10	1	48	183

*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.