Bad Air Days in Salt Lake County, Utah: 30 a Year

30 bad air days a year

Among the worst tenth of monitored US counties. Ranked 14 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (24% particle days).

When the bad days come in Salt Lake

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

What to buy, and what not to

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.
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 51 bad days a year; in 2016 to 2025, 30. The air has improved. The worst recent year was 2021, with 48 bad days on 365 monitored days.

Date	AQI	Main pollutant
2024-03-02	230	PM10
2020-07-05	214	PM2.5
2021-07-12	177	Ozone
2025-05-12	175	PM10
2018-06-27	169	Ozone

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in Salt Lake County rated Good on 36% of them, less often than the 72% typical of monitored counties, and Moderate on 55%. The median day sat at AQI 57; one day in ten went above 96.

The pollutant setting the AQI on an ordinary day here:

ozone60%2,209 days
fine particles (PM2.5)33%1,211 days
nitrogen dioxide5%170 days
coarse dust (PM10)2%63 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	121	228	16	1	57	175
2024	366	150	173	43	5	54	230
2023	365	149	200	16	1	54	154
2022	365	101	236	28	0	60	147
2021	365	122	195	48	9	59	177
2020	366	143	200	23	2	54	214
2019	365	132	216	17	0	58	136
2018	365	117	207	41	2	61	169
2017	365	131	190	44	1	60	156
2016	366	165	174	27	4	53	158
2015	365	163	175	27	2	54	154
2014	365	201	142	22	2	49	155
2013	365	169	146	50	8	52	163
2012	366	151	198	17	1	54	151
2011	365	171	164	30	3	51	160
2010	365	166	176	23	8	52	501

*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.