Bad Air Days in Fremont County, Wyoming: 2 a Year

2 bad air days a year

About the middle of monitored US counties. Ranked 437 of 996 monitored counties, where 1 is worst.

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

Which months to watch

Most bad days here fall in August and September and July and April. Averaged over 2016 to 2025.

What actually helps 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

In 2000 to 2009 this county averaged 6 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2021, with 8 bad days on 365 monitored days.

Date	AQI	Main pollutant
2020-09-03	161	PM2.5
2020-08-22	150	Ozone
2020-08-21	142	PM2.5
2021-08-31	141	PM2.5
2024-10-05	139	PM2.5

An ordinary day in Fremont

Across 3,653 monitored days from 2016 to 2025, the air in Fremont County rated Good on 70% of them, close to the 72% typical of monitored counties, and Moderate on 30%. The median day sat at AQI 46; one day in ten went above 65.

The pollutant setting the AQI on an ordinary day here:

ozone83%3,037 days
fine particles (PM2.5)17%604 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	254	111	0	0	47	100
2024	366	210	151	5	0	49	139
2023	365	215	147	3	0	49	110
2022	365	254	111	0	0	46	100
2021	365	240	117	8	0	46	141
2020	366	282	78	6	1	45	161
2019	365	291	73	1	0	45	122
2018	365	250	115	0	0	46	97
2017	365	249	114	2	0	47	118
2016	366	298	68	0	0	44	84
2015	365	276	89	0	0	45	97
2014	365	294	70	1	0	45	105
2013	365	259	106	0	0	46	100
2012	366	214	147	5	0	47	117
2011	365	201	162	2	0	49	136
2010	365	228	136	1	0	48	112

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

Elsewhere in Wyoming

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.