Cities with the Cleanest Air in America (EPA AQS Data)

EPA Air Quality System monitors run in most major US cities. Their data — not industry rankings or real estate listings — is the authoritative source on which cities actually have clean air. Here are the top 25.

Top 25 Cleanest-Air Cities (by Median AQI)

Rank	City	Median AQI	Unhealthy Days (5y)	Grade
1	Caguas, PR	6	5	A
2	Cook, MN	13	5	A
3	Anchorage, AK	21	12	A
4	Bayamon, PR	22	0	A
5	Alamosa, CO	22	2	A
6	Lubbock, TX	25	4	B
7	Twin Falls, ID	25	16	B
8	Victoria, TX	31	0	B
9	Honolulu, HI	31	1	B
10	Athens, OH	31	1	B
11	San Mateo, CA	31	12	B
12	Elko, NV	31	16	C
13	San Francisco, CA	32	10	B
14	Clackamas, OR	34	20	B
15	Chelan, WA	34	46	C
16	Santa Cruz, CA	36	21	B
17	Lorain, OH	37	2	B
18	Bennington, VT	38	7	B
19	Arlington, VA	38	9	B
20	Aiken, SC	39	0	B
21	Worcester, MA	39	7	C
22	Boise, ID	39	31	C
23	Ashland, WI	40	10	C
24	Delaware, OH	41	2	B
25	Chesterfield, VA	41	2	B

What Median AQI Actually Measures

The Air Quality Index combines readings for ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. EPA monitors sample these continuously; the median is the middle reading across every sampled day.

A city with median AQI 35 and only a handful of unhealthy days is consistently clean. A city with median AQI 42 but hundreds of unhealthy days has seasonal problems — usually wildfire smoke or winter inversions — that a single median number hides.

Caveats

Monitors aren’t everywhere. Small cities may rely on a single station, which under-samples neighborhood variation.
Wildfire years distort medians. A five-year window smooths this, but a single brutal year still pulls medians up.
Indoor air may be worse. Outdoor AQI is the headline, but natural gas stoves and poor ventilation can make a clean-air city’s apartments worse than the EPA number suggests.

Related Rankings

FAQ

Which US city has the cleanest air?

Caguas, PR currently has the lowest median AQI in the MoveScore dataset at 6, with 5 unhealthy air days over the last five years per EPA Air Quality System monitoring.

What is a "good" AQI?

The EPA defines 0-50 AQI as Good, 51-100 as Moderate, and 101+ as Unhealthy for sensitive groups or worse. A median AQI below 40 means most days are genuinely clean; above 60 means most days are merely moderate, with regular unhealthy days.

Why do some clean-air cities still have unhealthy days?

Median AQI measures typical days, but wildfires, inversions, and wind patterns create unhealthy-day spikes even in otherwise clean cities. A low-median city with a high unhealthy-day count has seasonal air problems, usually wildfire smoke.

Sources: EPA Air Quality System, EPA AirNow

Last updated: April 2026

Ranking uses EPA AQS median AQI across the last five years of monitored days, with unhealthy-day count (AQI >100) as tiebreaker.