Bad Air Days in Washington County, Utah: under 1 a Year

under 1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 688 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (20% particle days).

The bad-air season here

Most bad days here fall in August and June. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 8 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2020, with 3 bad days on 366 monitored days.

Date	AQI	Main pollutant
2021-08-07	163	PM2.5
2021-08-08	124	PM2.5
2020-08-21	112	Ozone
2018-08-07	108	Ozone
2021-06-10	108	Ozone

The air on a normal day

Across 3,653 monitored days from 2016 to 2025, the air in Washington County rated Good on 74% of them, close to the 72% typical of monitored counties, and Moderate on 26%. The median day sat at AQI 44; one day in ten went above 65.

The pollutant setting the AQI on an ordinary day here:

ozone92%3,351 days
fine particles (PM2.5)8%300 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	274	91	0	0	44	97
2024	366	278	86	2	0	44	108
2023	365	291	74	0	0	43	90
2022	365	288	77	0	0	44	97
2021	365	256	106	3	1	45	163
2020	366	276	87	3	0	44	112
2019	365	283	82	0	0	45	93
2018	365	223	141	1	0	44	108
2017	365	256	108	1	0	45	101
2016	366	281	85	0	0	43	87
2015	365	276	86	3	0	43	108
2014	365	284	80	1	0	44	101
2013	365	274	89	2	0	44	112
2012	366	228	126	12	0	47	133
2011	363	235	123	5	0	46	108
2010	365	210	147	8	0	48	108

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

Elsewhere in Utah

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.