National ranking · cleanest air

Best Air Quality in the US (2025)

Ranked by the highest share of Good air days among counties with at least 100 monitored days in 2025, the counties where residents breathe the cleanest air most often, from EPA Air Quality System monitoring.

100.0%
#1 Sonoma, California
46
Counties ranked

Sonoma County, California leads the 2025 cleanest-air list among 46 ranked U.S. counties (100.0% Good)

According to the U.S. EPA Air Quality System, this ranking orders 46 counties with at least 100 monitored days in 2025 by the highest share of days in the Good AQI band, using median AQI to separate near-ties. It describes a historical reporting year, not today's air quality. For current conditions and alerts, use AirNow.

Data source EPA Air Quality System (AQS)

#1 Good-day share
Sonoma County, California ranks #1 of 46 for Good-day share at 100.0%.
#1 median AQI
#1 median AQI: 9
Counties ranked
Counties ranked: 46
Tied at 100% Good
Tied at 100% Good: 1

from the compiled EPA AQS release in this database.

Counties below the 100-day monitoring floor are excluded: with only a handful of readings, a single clean stretch can push a county to a 100% Good-day rate that a normal year's weather would not hold up. 1 counties tie at 100.0% with this floor applied, all with a genuinely large sample of monitored days. For comparison, the cohort median across all 951 floor-qualifying counties is 77.5%, meaning the difference between a top-ranked county and a typical monitored county is real, not sampling noise.

Filter this ranking

Clear

Filters keep the Good-day-share ranking contract. A state filter ranks that state's qualifying counties; pollutant filters keep rows whose annual day-type count is led by ozone, PM2.5, or PM10. Raising the monitored-days floor tightens the sample beyond the default 100-day Module-34 guard.

Compare up to three counties

Showing 46 matching California counties . Back to the national top 50.

Where the national cleanest cohort concentrates

Among the unfiltered national top 50 (highest Good-day share, ≥100 monitored days), Virginia contributes 6 counties , followed by Wyoming (4). State filters rank every qualifying county inside one jurisdiction.

Compare any two counties

For a side-by-side annual change view, open the county compare tool.

Cleanest of the clean: lowest median AQI

Cleanest of the clean: lowest median AQI

Among the top counties (all near a 100% Good-day record), the lowest typical AQI. Shorter is cleaner.

  1. 1 Sonoma, California 9
  2. 2 Mono, California 21
  3. 3 Lake, California 31
  4. 4 Trinity, California 31
  5. 5 Del Norte, California 32
  6. 6 Solano, California 33
  7. 7 Santa Cruz, California 35
  8. 8 Siskiyou, California 37
  9. 9 Amador, California 38
  10. 10 Monterey, California 38
  11. 11 Humboldt, California 38
  12. 12 Tehama, California 38

Median AQI · EPA Air Quality System

Ranked counties

# County State Good Days % Median AQI
1 Sonoma California 100.0% 9 Good
2 Lake California 99.2% 31 Good
3 Solano California 99.2% 33 Good
4 San Benito California 91.5% 39 Good
5 Mono California 90.1% 21 Good
6 Santa Cruz California 87.7% 35 Good
7 El Dorado California 87.7% 40 Good
8 Amador California 87.4% 38 Good
9 Tuolumne California 87.0% 39 Good
10 Monterey California 86.0% 38 Good
11 Calaveras California 82.2% 40 Good
12 Del Norte California 81.8% 32 Good
13 Mariposa California 80.6% 44 Good
14 Glenn California 80.0% 40 Good
15 Nevada California 79.8% 42 Good
16 Colusa California 79.2% 40 Good
17 Siskiyou California 78.2% 37 Good
18 Humboldt California 78.1% 38 Good
19 Tehama California 77.8% 38 Good
20 Shasta California 75.6% 44 Good
21 Mendocino California 73.7% 38 Good
22 Trinity California 69.6% 31 Good
23 Butte California 65.2% 46 Good
24 Sutter California 63.2% 47 Good
25 San Joaquin California 60.0% 46 Good
26 Yolo California 58.4% 47 Good
27 Sacramento California 54.3% 49 Good
28 Plumas California 52.9% 45 Good
29 San Luis Obispo California 52.3% 50 Good
30 Ventura California 52.0% 50 Good
31 Merced California 51.0% 50 Good
32 Madera California 50.4% 50 Good
33 Stanislaus California 49.9% 51 Moderate
34 Placer California 45.8% 52 Moderate
35 Santa Barbara California 44.9% 52 Moderate
36 Orange California 37.8% 53 Moderate
37 Inyo California 37.3% 55 Moderate
38 Kings California 34.5% 57 Moderate
39 Fresno California 28.8% 61 Moderate
40 Imperial California 27.7% 64 Moderate
41 Tulare California 24.1% 64 Moderate
42 San Diego California 17.5% 67 Moderate
43 Kern California 17.5% 70 Moderate
44 San Bernardino California 12.6% 77 Moderate
45 Los Angeles California 10.7% 74 Moderate
46 Riverside California 10.7% 80 Moderate

Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS). Good Days % is the share of monitored days with AQI at or below 50. Counties ranked by good_pct descending

Embed this widget

Copy this snippet to embed a live-linked card on your own site. Attribution to PlainAirData is baked into the widget.

Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.