Bad Air Days in Johnson County, Wyoming: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 645 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (11% particle days).

Which months to watch

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

What to buy, and what not to

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 record for Johnson

The worst recent year was 2021, with 7 bad days on 365 monitored days.

Date	AQI	Main pollutant
2021-08-02	126	Ozone
2021-07-19	112	Ozone
2021-07-27	112	Ozone
2021-08-01	112	Ozone
2024-07-23	112	Ozone

Most days, not the worst ones

Across 2,777 monitored days from 2018 to 2025, the air in Johnson County rated Good on 92% of them, more often than the 72% typical of monitored counties, and Moderate on 8%. The median day sat at AQI 40; one day in ten went above 52.

The pollutant setting the AQI on an ordinary day here:

ozone97%2,683 days
coarse dust (PM10)3%82 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Median AQI	Highest AQI
2025*	363	337	26	0	41	84
2024	364	327	36	1	40	112
2023	364	351	13	0	40	64
2022	365	350	14	1	39	101
2021	365	304	54	7	40	126
2020	364	337	27	0	40	93
2019	364	345	19	0	40	80
2018	228	190	38	0	39	90
2015	57	56	1	0	8	61
2014	114	111	3	0	8	68
2013	103	101	2	0	9	73
2012	117	108	9	0	11	66
2011	105	103	2	0	9	55
2010	107	107	0	0	8	39

*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.