Bad Air Days in Davis County, Utah: 15 a Year

15 bad air days a year

Among the worst tenth of monitored US counties. Ranked 52 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (23% particle days).

Which months to watch

Most bad days here fall in July and August. 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.
Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
Sign up for EnviroFlash ozone alerts for this area during the worst months.

Better or worse than it was

In 2000 to 2009 this county averaged 20 bad days a year; in 2016 to 2025, 15. The air has improved. The worst recent year was 2017, with 28 bad days on 365 monitored days.

Date	AQI	Main pollutant
2020-08-21	157	PM2.5
2021-07-26	156	Ozone
2018-06-27	151	Ozone
2023-08-15	151	Ozone
2022-08-09	147	Ozone

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in Davis County rated Good on 59% of them, less often than the 72% typical of monitored counties, and Moderate on 37%. The median day sat at AQI 47; one day in ten went above 83.

The pollutant setting the AQI on an ordinary day here:

ozone67%2,441 days
fine particles (PM2.5)27%983 days
nitrogen dioxide6%219 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	231	127	7	0	46	119
2024	366	234	117	15	0	46	133
2023	365	211	141	13	1	47	151
2022	365	210	145	10	0	47	147
2021	365	205	134	26	1	47	156
2020	366	217	135	14	1	46	157
2019	365	239	120	6	0	45	119
2018	365	194	158	13	1	49	151
2017	365	180	157	28	0	51	140
2016	366	224	128	14	0	47	143
2015	357	270	80	7	0	39	143
2014	365	265	89	11	0	44	130
2013	360	281	68	11	0	42	140
2012	366	288	78	0	0	41	100
2011	363	294	65	4	1	40	152
2010	365	287	68	10	1	40	152

*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.