Bad Air Days in Calaveras County, California: 10 a Year

10 bad air days a year

Among the worst tenth of monitored US counties. Ranked 86 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (45% particle days).

The bad-air season here

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

What actually helps 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.

The worst days on file

In 2000 to 2009 this county averaged 41 bad days a year; in 2016 to 2025, 10. The air has improved. The worst recent year was 2020, with 23 bad days on 364 monitored days.

Date	AQI	Main pollutant
2020-08-21	210	PM2.5
2020-08-20	195	PM2.5
2020-08-22	194	PM2.5
2020-08-23	192	PM2.5
2020-09-15	190	PM2.5

An ordinary day in Calaveras

Across 3,619 monitored days from 2016 to 2025, the air in Calaveras County rated Good on 61% of them, less often than the 72% typical of monitored counties, and Moderate on 36%. The median day sat at AQI 46; one day in ten went above 72.

The pollutant setting the AQI on an ordinary day here:

ozone62%2,249 days
fine particles (PM2.5)38%1,358 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	359	295	64	0	0	40	100
2024	359	261	90	8	0	42	129
2023	365	292	72	1	0	40	101
2022	364	286	77	1	0	41	115
2021	364	220	135	9	3	46	178
2020	364	206	135	23	13	48	210
2019	360	288	71	1	0	43	108
2018	364	52	292	20	6	58	160
2017	354	118	222	14	2	57	172
2016	366	195	149	22	0	49	150
2015	365	216	127	22	4	47	390
2014	361	209	148	4	0	47	115
2013	364	172	190	2	0	51	119
2012	366	213	140	13	1	47	156
2011	364	164	189	11	0	52	143
2010	365	249	103	13	1	44	154

*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.