Bad Air Days in Fresno County, California: 81 a Year

81 bad air days a year

Among the worst tenth of monitored US counties. Ranked 7 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (34% particle days).

When the bad days come in Fresno

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.
With this many bad days, whole-home filtration is worth an HVAC contractor quote.
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 163 bad days a year; in 2016 to 2025, 81. The air has improved. The worst recent year was 2017, with 120 bad days on 365 monitored days.

Date	AQI	Main pollutant
2020-09-13	346	PM2.5
2020-09-14	290	PM10
2021-01-19	278	PM10
2020-09-16	274	PM2.5
2020-09-17	259	PM2.5

The air on a normal day

Across 3,653 monitored days from 2016 to 2025, the air in Fresno County rated Good on 22% of them, less often than the 72% typical of monitored counties, and Moderate on 56%. The median day sat at AQI 70; one day in ten went above 127.

The pollutant setting the AQI on an ordinary day here:

ozone53%1,939 days
fine particles (PM2.5)44%1,598 days
coarse dust (PM10)3%113 days

Fresno County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	105	226	34	3	61	164
2024	366	71	216	79	14	67	169
2023	365	97	210	58	3	64	156
2022	365	78	217	70	3	71	159
2021	365	62	221	82	19	68	278
2020	366	75	192	99	40	76	346
2019	365	113	186	66	2	63	187
2018	365	61	206	98	19	75	185
2017	365	76	169	120	27	75	207
2016	366	62	199	105	25	76	190
2015	365	38	225	102	24	80	205
2014	365	48	193	124	33	83	197
2013	365	35	191	139	25	88	197
2012	366	45	187	134	42	82	212
2011	365	26	216	123	40	80	197
2010	365	48	230	87	22	71	209

*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.