Bad Air Days in Placer County, California: 21 a Year

21 bad air days a year

Among the worst tenth of monitored US counties. Ranked 28 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (39% particle days).

The bad-air season here

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.
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.

The worst days on file

In 2000 to 2009 this county averaged 62 bad days a year; in 2016 to 2025, 21. The air has improved. The worst recent year was 2021, with 48 bad days on 365 monitored days.

Date	AQI	Main pollutant
2021-08-23	692	PM2.5
2021-08-22	463	PM2.5
2022-09-16	442	PM2.5
2022-09-10	338	PM2.5
2021-08-21	312	PM2.5

An ordinary day in Placer

Across 3,653 monitored days from 2016 to 2025, the air in Placer County rated Good on 48% of them, less often than the 72% typical of monitored counties, and Moderate on 46%. The median day sat at AQI 51; one day in ten went above 88.

The pollutant setting the AQI on an ordinary day here:

ozone59%2,158 days
fine particles (PM2.5)40%1,456 days
nitrogen dioxide1%22 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	167	196	2	0	52	143
2024	366	188	151	27	0	50	140
2023	365	164	193	8	0	52	143
2022	365	156	185	24	9	54	442
2021	365	130	187	48	18	58	692
2020	366	130	195	41	21	57	247
2019	365	198	158	9	0	49	136
2018	365	213	127	25	9	46	248
2017	365	211	145	9	2	46	156
2016	366	187	159	20	3	50	166
2015	365	179	177	9	1	51	189
2014	365	116	221	28	5	57	265
2013	365	126	222	17	4	55	165
2012	366	145	180	41	6	54	170
2011	365	135	191	39	6	57	172
2010	365	127	208	30	4	55	200

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

Elsewhere in California

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.