Bad Air Days in Riverside County, California: 132 a Year

132 bad air days a year

Among the worst tenth of monitored US counties. Ranked 2 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (19% particle days).

Which months to watch

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.
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.

The record for Riverside

In 2000 to 2009 this county averaged 170 bad days a year; in 2016 to 2025, 132. The air has improved. The worst recent year was 2017, with 151 bad days on 365 monitored days.

Date	AQI	Main pollutant
2022-05-28	1683	PM10
2022-05-29	1548	PM10
2022-05-08	792	PM10
2022-04-11	660	PM10
2023-04-13	660	PM10

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in Riverside County rated Good on 10% of them, less often than the 72% typical of monitored counties, and Moderate on 54%. The median day sat at AQI 83; one day in ten went above 156.

The pollutant setting the AQI on an ordinary day here:

ozone56%2,051 days
fine particles (PM2.5)32%1,165 days
coarse dust (PM10)12%434 days

Riverside County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	39	217	109	34	80	365
2024	366	43	176	147	67	87	213
2023	365	62	189	114	41	77	660
2022	365	41	198	126	40	77	1683
2021	365	19	210	136	47	89	329
2020	366	42	179	145	47	87	584
2019	365	53	192	120	29	77	185
2018	365	32	193	140	38	87	296
2017	365	26	188	151	51	87	359
2016	366	23	214	129	43	83	379
2015	365	19	206	140	34	88	238
2014	365	11	198	156	34	93	541
2013	365	19	210	136	38	88	450
2012	366	10	189	167	54	94	233
2011	365	15	195	155	59	93	318
2010	365	11	208	146	51	87	217

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

California compared

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, and on why a purifier does not touch ozone in smoke vs ozone.