Bad Air Days in Rosebud County, Montana: 4 a Year

4 bad air days a year

About the middle of monitored US counties. Ranked 288 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (97% particle days).

When the bad days come in Rosebud

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

Is a purifier worth it here?

Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.

The record for Rosebud

In 2000 to 2009 this county averaged 1 bad days a year; in 2016 to 2025, 4. It has got worse. The worst recent year was 2021, with 14 bad days on 363 monitored days.

Date	AQI	Main pollutant
2017-07-11	196	PM2.5
2017-09-13	166	PM2.5
2017-07-09	158	PM2.5
2017-09-02	155	PM2.5
2021-08-16	155	PM2.5

Most days, not the worst ones

Across 3,276 monitored days from 2016 to 2025, the air in Rosebud County rated Good on 87% of them, more often than the 72% typical of monitored counties, and Moderate on 11%. The median day sat at AQI 26; one day in ten went above 47.

The pollutant setting the AQI on an ordinary day here:

ozone44%1,453 days
fine particles (PM2.5)25%815 days
nitrogen dioxide20%639 days
coarse dust (PM10)11%369 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	98	96	2	0	0	11	68
2024	366	353	13	0	0	4	90
2023	285	279	5	1	0	3	132
2022	337	337	0	0	0	2	36
2021	363	266	83	14	2	38	155
2020	366	321	40	5	2	37	154
2019	365	328	36	1	0	36	108
2018	365	302	61	2	0	38	133
2017	365	277	77	11	6	39	196
2016	366	307	58	1	0	38	132
2015	365	274	82	9	1	40	156
2014	365	293	69	3	0	39	115
2013	365	313	48	4	0	39	113
2012	365	241	118	6	0	44	145
2011	365	310	51	4	0	39	150
2010	365	334	29	2	0	35	108

*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.