Bad Air Days in Sheridan County, Montana

Not enough data

EPA monitors in Sheridan County ran on too few days between 2016 and 2025 to give a fair yearly count (about 30% of days covered). Neighbouring counties below are a better guide.

Is a purifier worth it here?

EPA monitors here ran too few days to give a fair yearly count. Use AirNow for today's air.

The record for Sheridan

The worst recent year was 2023, with 4 bad days on 112 monitored days.

Date	AQI	Main pollutant
2025-07-12	197	PM2.5
2023-07-14	160	PM2.5
2023-09-03	136	PM2.5
2024-07-23	126	PM2.5
2023-08-07	124	PM2.5

Most days, not the worst ones

Across 1,085 monitored days from 2016 to 2025, the air in Sheridan County rated Good on 92% of them, more often than the 72% typical of monitored counties, and Moderate on 7%. The median day sat at AQI 17; one day in ten went above 44.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%1,085 days

Sheridan County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	91	79	11	1	1	18	197
2024	119	104	13	2	0	17	126
2023	112	96	12	4	1	18	160
2022	89	85	4	0	0	16	66
2021	120	108	12	0	0	17	98
2020	107	103	4	0	0	13	58
2019	104	101	3	0	0	16	57
2018	112	99	12	1	0	20	118
2017	114	109	5	0	0	17	75
2016	117	113	4	0	0	15	81
2015	115	109	3	3	1	16	155
2014	114	109	5	0	0	17	74
2013	107	102	5	0	0	19	70
2012	107	100	7	0	0	18	96
2011	115	111	4	0	0	17	56
2010	113	107	5	1	0	17	102

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

Elsewhere in Montana

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.