US Air Quality

25 Most Polluted US Cities

The most polluted based on average AQI measurements and air quality data.

The short answer

By median AQI across the full 2025 EPA record, Riverside, CA was the most polluted metro area we track: median AQI 87, 136 days above AQI 100 and 53 days above AQI 150, with ground-level ozone setting the daily AQI on 207 days. Good-air days: 27 of 365 (7.4%).

US cities ranked from EPA annual AQI summaries for 2025
#	City (EPA area)	Good days (2025)	Median AQI	Days over 100	Days over 150	Main pollutant	AQI now
1	Riverside, CARiverside-San Bernardino-Ontario, CA	27 / 365 (7.4%)	87	136	53	ground-level ozone	172
2	Mesa, AZPhoenix-Mesa-Scottsdale, AZ	24 / 365 (6.6%)	78	56	13	coarse dust (PM10)	37
3	Phoenix, AZPhoenix-Mesa-Scottsdale, AZ	24 / 365 (6.6%)	78	56	13	coarse dust (PM10)	47
4	Scottsdale, AZPhoenix-Mesa-Scottsdale, AZ	24 / 365 (6.6%)	78	56	13	coarse dust (PM10)	47
5	Irvine, CALos Angeles-Long Beach-Anaheim, CA	39 / 365 (10.7%)	74	99	32	ground-level ozone	56
6	Long Beach, CALos Angeles-Long Beach-Anaheim, CA	39 / 365 (10.7%)	74	99	32	ground-level ozone	50
7	Los Angeles, CALos Angeles-Long Beach-Anaheim, CA	39 / 365 (10.7%)	74	99	32	ground-level ozone	32
8	Bakersfield, CABakersfield, CA	64 / 365 (17.5%)	70	65	4	ground-level ozone	129
9	El Paso, TXEl Paso, TX	66 / 365 (18.1%)	70	63	30	coarse dust (PM10)	40
10	San Diego, CASan Diego-Carlsbad, CA	64 / 365 (17.5%)	67	33	7	fine particulate matter (PM2.5)	54
11	Visalia, CAVisalia-Porterville, CA	88 / 365 (24.1%)	64	43	0	ground-level ozone	90
12	Houston, TXHouston-The Woodlands-Sugar Land, TX	37 / 365 (10.1%)	63	46	11	fine particulate matter (PM2.5)	77
13	Fresno, CAFresno, CA	105 / 365 (28.8%)	61	34	3	ground-level ozone	93
14	Las Vegas, NVLas Vegas-Henderson-Paradise, NV	113 / 365 (31%)	61	26	0	ground-level ozone	49
15	Albuquerque, NMAlbuquerque, NM	91 / 365 (24.9%)	61	21	3	ground-level ozone	32
16	Dallas, TXDallas-Fort Worth-Arlington, TX	103 / 365 (28.2%)	59	45	5	fine particulate matter (PM2.5)	122
17	Fort Worth, TXDallas-Fort Worth-Arlington, TX	103 / 365 (28.2%)	59	45	5	fine particulate matter (PM2.5)	122
18	Aurora, CODenver-Aurora-Lakewood, CO	105 / 365 (28.8%)	58	17	0	ground-level ozone	41
19	Denver, CODenver-Aurora-Lakewood, CO	105 / 365 (28.8%)	58	17	0	ground-level ozone	41
20	Salt Lake City, UTSalt Lake City, UT	120 / 365 (32.9%)	57	17	1	ground-level ozone	44
21	Brownsville, TXBrownsville-Harlingen, TX	109 / 365 (29.9%)	57	8	0	fine particulate matter (PM2.5)	39
22	Aurora, ILChicago-Naperville-Elgin, IL-IN-WI	109 / 365 (29.9%)	56	32	6	fine particulate matter (PM2.5)	31
23	Chicago, ILChicago-Naperville-Elgin, IL-IN-WI	109 / 365 (29.9%)	56	32	6	fine particulate matter (PM2.5)	31
24	St. Louis, MOSt. Louis, MO-IL	114 / 365 (31.2%)	56	15	4	fine particulate matter (PM2.5)	29
25	Cincinnati, OHCincinnati, OH-KY-IN	95 / 365 (26%)	56	15	2	fine particulate matter (PM2.5)	42

Figures are EPA's published annual AQI summaries by metropolitan area (Annual AQI by CBSA, 2019–2025), retrieved 2026-09-07. The daily AQI EPA summarises is the highest value any monitor in the area reported that day, so these are metro-area readings, not statewide or rural ones. Only cities with at least 300 reported days in 2025 are ranked — a partial year cannot be compared fairly against a full one — and cities in areas EPA publishes no summary for are left out rather than given an estimated value. "AQI now" is the latest AirNow observation at build time and is blank where AirNow has none.

Why these cities rank where they do

The ranking is by the area's median AQI — the typical day, not the worst one — so a single smoke event does not put a city at the top. Where the dominant pollutant column reads Ozone, the pollution is largely photochemical and peaks on hot, sunny, still afternoons. Where it reads PM2.5, the driver is combustion: traffic, industry, wood smoke or wildfire, and it peaks in winter inversions or smoke season.

Geography does much of the work. Basins and valleys (the San Joaquin, the Salt Lake Valley, the Los Angeles basin) trap air under a lid of warm air above; coastal and windy cities clear theirs. Compare any two areas side by side on the city comparison pages.

About This Ranking

This ranking is based on Air Quality Index (AQI) measurements from EPA monitoring stations across the United States. Cities with higher AQI values have more polluted air.

What Makes Air Quality Poor?

Cities with poor air quality often face challenges like geographic basins that trap pollution, high population density, industrial emissions, heavy traffic, wildfire smoke, or unfavorable weather patterns like temperature inversions.

Data Sources

Rankings are based on current AQI data from the EPA AirNow system, which monitors pollution levels continuously.