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Riverside-San Bernardino-Ontario, CA Air Quality

EPA monitor data through 2025 · Updated August 13, 2026 · Methods

In 2025, Riverside-San Bernardino-Ontario, CA recorded 136 days above an Air Quality Index of 100, the level at which EPA begins warning sensitive groups, out of 365 days with monitoring data. Most of those bad days were driven by ozone. Under the AQI rules that applied before 2013, the same air would have scored 108 days. Since 2000, unhealthy days are 41% lower on a consistent definition.

Unhealthy days, 2025

136

AQI above 100

Same air, pre-2013 rules

108

for comparison with older reports

Good-air days

AQI 50 or below

Days monitored

365

full year

Unhealthy days by year, scored two ways

EPA changed what an AQI of 100 means in 2013 and again in 2015, so a count published before those changes is not comparable to one published after. Each panel below applies a single fixed rulebook to every year, so each is internally consistent. Why this matters.

Scored by today's rules

Scored by the pre-2013 rules

Ozone since 1990

The index counts above only start in 2000, because nationwide fine-particle monitoring did not exist before 1999 and an index without it would measure the monitoring network rather than the air. Ozone does have a 35-year record. This is Riverside-San Bernardino-Ontario, CA's, from EPA's long-running trend monitors: 153 ppb in 1990 to 101 ppb in 2024, 34% lower.

Peak ozone, 1990 to 2024

Annual fourth-highest daily maximum 8-hour ozone, parts per billion, averaged across 11 long-running monitors in the area. The dashed line is the current standard, 70 ppb. Holding the monitor set still is what makes a 35-year comparison meaningful, and it is also why these values differ from the design value used for compliance. Source: EPA air quality statistics by city.

What 2025 looked like

Air quality category	Days	Share of monitored days
Good	27	7%
Moderate	202	55%
Unhealthy for sensitive groups	83	23%
Unhealthy or worse	53	15%

Median AQI 87 · 90th-percentile AQI 161 · worst day 365. Scored under current rules.

What drove the unhealthy days

Of the 136 days above 100 in 2025, 107 were driven by ozone and 14 by fine particles, with 15 from another pollutant. The two behave differently. Ozone peaks on hot sunny afternoons; fine particles now spike mainly with wildfire smoke. In the western United States, ozone is a different problem: the floor is rising, with even the cleanest summer days at high elevation now near 40 ppb, and bad years track wildfire seasons. Domestic emission cuts have less room to work against that.

The unhealthy days in 2025

Every day the index passed 100, what it reached, and which pollutant drove it. 28 of these 136 would not have counted as unhealthy under the pre-2013 rules.

Date	Peak AQI	Driven by	Pre-2013 score
Jan 1	166	Fine particles	157
Jan 4	136	Fine particles	119
Jan 7	365	Coarse particles	374
Jan 8	119	Coarse particles	119
Feb 1	112	Fine particles	99 (not unhealthy)
Feb 2	109	Fine particles	97 (not unhealthy)
Feb 11	164	Coarse particles	164
Mar 1	174	Coarse particles	174
Mar 6	142	Coarse particles	142
Mar 22	101	Ozone	87 (not unhealthy)
Mar 26	120	Coarse particles	120
Mar 27	127	Coarse particles	127
Mar 30	114	Coarse particles	114
Apr 8	122	Ozone	104
Apr 9	136	Ozone	114
Apr 10	154	Ozone	129
Apr 11	143	Ozone	119
Apr 16	112	Coarse particles	112
Apr 17	112	Coarse particles	112
Apr 18	136	Coarse particles	136
Apr 20	101	Ozone	87 (not unhealthy)
Apr 21	101	Ozone	87 (not unhealthy)
Apr 22	101	Ozone	87 (not unhealthy)
May 2	101	Ozone	87 (not unhealthy)
May 4	116	Coarse particles	116
May 8	129	Ozone	109
May 9	154	Ozone	129
May 10	150	Ozone	124
May 11	108	Ozone	93 (not unhealthy)
May 13	146	Coarse particles	146
May 17	158	Coarse particles	158
May 19	108	Ozone	93 (not unhealthy)
May 20	136	Ozone	114
May 21	169	Ozone	145
May 22	166	Ozone	142
May 23	126	Ozone	106
May 25	101	Ozone	87 (not unhealthy)
May 27	133	Ozone	111
May 28	105	Ozone	90 (not unhealthy)
May 29	156	Ozone	132
May 30	159	Ozone	135
May 31	118	Fine particles	105
Jun 4	108	Ozone	93 (not unhealthy)
Jun 5	105	Ozone	90 (not unhealthy)
Jun 6	140	Ozone	116
Jun 7	143	Ozone	119
Jun 8	133	Ozone	111
Jun 9	154	Ozone	129
Jun 10	187	Ozone	161
Jun 11	179	Ozone	154
Jun 12	150	Ozone	124
Jun 13	182	Ozone	156
Jun 14	161	Ozone	137
Jun 15	174	Ozone	150
Jun 16	195	Ozone	169
Jun 17	207	Ozone	192
Jun 18	205	Ozone	187
Jun 19	166	Ozone	142
Jun 20	122	Ozone	104
Jun 21	183	Coarse particles	183
Jun 25	156	Ozone	132
Jun 26	169	Ozone	145
Jun 27	151	Ozone	127
Jun 28	159	Ozone	135
Jun 29	129	Ozone	109
Jul 1	161	Ozone	137
Jul 2	150	Ozone	124
Jul 3	136	Ozone	114
Jul 4	108	Ozone	93 (not unhealthy)
Jul 5	153	Fine particles	136
Jul 6	150	Ozone	124
Jul 7	169	Ozone	145
Jul 8	166	Ozone	142
Jul 9	172	Ozone	147
Jul 10	201	Ozone	177
Jul 11	169	Ozone	145
Jul 12	150	Ozone	124
Jul 13	151	Ozone	127
Jul 14	182	Ozone	156
Jul 15	133	Ozone	111
Jul 16	112	Ozone	97 (not unhealthy)
Jul 17	101	Ozone	87 (not unhealthy)
Jul 18	133	Ozone	111
Jul 19	136	Ozone	114
Jul 20	112	Ozone	97 (not unhealthy)
Jul 22	101	Ozone	87 (not unhealthy)
Jul 23	101	Ozone	87 (not unhealthy)
Jul 27	119	Ozone	101
Jul 28	136	Ozone	114
Jul 29	147	Ozone	122
Jul 30	133	Ozone	111
Jul 31	136	Ozone	114
Aug 1	119	Ozone	101
Aug 2	140	Ozone	116
Aug 3	161	Ozone	137
Aug 4	166	Ozone	142
Aug 5	156	Ozone	132
Aug 6	190	Ozone	164
Aug 7	159	Ozone	135
Aug 8	156	Ozone	132
Aug 9	147	Ozone	122
Aug 10	140	Ozone	116
Aug 11	187	Ozone	161
Aug 12	192	Ozone	166
Aug 13	166	Ozone	142
Aug 14	156	Ozone	132
Aug 15	140	Ozone	116
Aug 18	150	Ozone	124
Aug 19	161	Ozone	137
Aug 20	182	Ozone	156
Aug 21	202	Ozone	179
Aug 22	187	Ozone	161
Aug 23	126	Ozone	106
Aug 24	179	Ozone	154
Aug 25	115	Ozone	100 (not unhealthy)
Aug 26	105	Ozone	90 (not unhealthy)
Aug 29	143	Ozone	119
Aug 30	177	Ozone	151
Aug 31	147	Ozone	122
Sep 1	129	Ozone	109
Sep 3	166	Ozone	142
Sep 4	147	Ozone	122
Sep 14	133	Ozone	111
Sep 15	129	Ozone	109
Sep 16	115	Ozone	100 (not unhealthy)
Sep 17	101	Ozone	87 (not unhealthy)
Sep 23	112	Ozone	97 (not unhealthy)
Oct 19	119	Ozone	101
Nov 2	108	Fine particles	96 (not unhealthy)
Nov 12	105	Fine particles	93 (not unhealthy)
Nov 30	109	Fine particles	96 (not unhealthy)
Dec 13	147	Fine particles	128
Dec 14	162	Fine particles	155
Dec 15	137	Fine particles	120
Dec 17	118	Fine particles	105
Dec 21	105	Fine particles	93 (not unhealthy)

Statewide context

Riverside-San Bernardino-Ontario, CA sits in California.

The full series

Year	Unhealthy days, current rules	Pre-2013 rules	Days monitored
2000	204	183	366
2001	220	195	365
2002	203	180	365
2003	186	164	365
2004	189	164	366
2005	174	143	365
2006	164	139	365
2007	203	172	365
2008	169	152	366
2009	166	134	365
2010	161	130	365
2011	171	141	365
2012	182	136	366
2013	157	123	365
2014	175	135	365
2015	169	133	365
2016	161	129	366
2017	174	144	365
2018	173	136	365
2019	145	116	365
2020	176	153	366
2021	166	142	365
2022	150	129	365
2023	140	116	365
2024	164	146	366
2025	136	108	365

Sources

EPA AirData daily monitor files, recomputed under both breakpoint tables. Methods and validation.
Download the full dataset for every state and metro.