Median AQI
54
Moderate
California · County air quality · 2025
San Diego County, California
Median AQI 54 (Moderate). 42.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 54
- Median AQI
- 42.6%
- Good-air days
- 5
- Unhealthy days
- 4%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, San Diego County's air is moderate on balance, among the most polluted counties nationally, a median AQI of 54 with 42.6% of 272 monitored days in the Good band, driven mainly by Ozone.
- 54
- median AQI · Moderate
- 42.6%
- days rated Good
- Ozone
- main pollutant
- 4%
- cleaner than US counties
5 days reached Unhealthy or worse; the worst single reading hit AQI 161.
Data updated July 2026
- Good · 116 d · 42.6%
- Moderate · 136 d · 50.0%
- USG · 15 d · 5.5%
- Unhealthy · 5 d · 1.8%
How did San Diego County's air break down in 2025?
Across 272 monitored days, 116 fell in the Good band (AQI 0–50) and 5 reached Unhealthy or worse. The worst single day peaked at AQI 161 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 272 days monitored. Median AQI: 54 (Moderate).
Insights: San Diego County, California. EPA monitors recorded a median Air Quality Index of 54 across 272 measured days in 2025, earning a Moderate classification and a Poor health grade. Of those days, 116 (43%) fell in the Good band (AQI 0–50), 136 (50%) registered Moderate readings, and 15 (6%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 93, while the worst single-day peak hit 161 (Unhealthy). Residents averaged about 12.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (178 days), PM2.5 (94 days). Across the 2020–2025 trend window, good days shifted by +83 and the median AQI moved -20 points, placing the multi-year trajectory at improving. Residents and visitors experienced 5 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Amador (84.8% good, AQI 40); Butte (66.1% good, AQI 47); Calaveras (73.9% good, AQI 43); Colusa (84.9% good, AQI 39); Del Norte (81.0% good, AQI 33); El Dorado (85.8% good, AQI 39).
Air Quality Summary
Good Days
42.6%
116 of 272 monitored days
-32.4pp vs 75% target
Max AQI Recorded
161
Unhealthy
Health Grade
Poor
90th-pct AQI 93
San Diego County, Good days share 42.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
San Diego County, Unhealthy-or-worse share 1.8%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 272 monitored days across EPA AQI categories.
Good
116
43%
Moderate
136
50%
USG
15
6%
Unhealthy
5
2%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in San Diego County.
- Ozone · 178 days · 65.4%
- PM2.5 · 94 days · 34.6%
Health Impact Assessment
Poor
San Diego County's air quality is rated Poor based on 42.6% good air days. There were 5 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 15 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 161. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is Ozone, driving AQI on 178 of 272 monitored days.
5-Year Air Quality Trend
Air quality is improving in San Diego County. Best year: 2025 (116 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 33 | 284 | 35 | 14 | 74 | 192 |
| 2021 | 52 | 297 | 16 | 0 | 67 | 133 |
| 2022 | 42 | 297 | 25 | 1 | 63 | 156 |
| 2023 | 61 | 260 | 44 | 0 | 67 | 150 |
| 2024 | 47 | 267 | 48 | 4 | 71 | 161 |
| 2025 | 116 | 136 | 15 | 5 | 54 | 161 |
How does San Diego County compare?
How San Diego County compares
Good-day share worse than US avg
San Diego County 42.6%
Amador County, California 84.8%
US average 76.5%
Median AQI worse than US avg
San Diego County 54
Amador County, California 40
US average 38
Unhealthy days / yr worse than US avg
San Diego County 5
Amador County, California 0
US average 0
Other Counties in California
Air quality comparison for nearby counties in California.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to San Diego County.
Denver County, Colorado
AQI 54 · 44.2% good
Franklin County, Ohio
AQI 54 · 39.8% good
Fresno County, California
AQI 54 · 40.1% good
Hamilton County, Ohio
AQI 54 · 32.1% good
Hidalgo County, Texas
AQI 54 · 36.2% good
Inyo County, California
AQI 54 · 40.7% good
What San Diego County's air means for you
On most days the air here is fine, but Ozone drives 5 unhealthy-or-worse days a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 54 means for exposure. Health guidance
- See how San Diego County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare San Diego County with its California neighbours before drawing a conclusion about the region. All of California
Based on 272 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in San Diego County, California? ▼
San Diego County has a median Air Quality Index (AQI) of 54, rated "Moderate." 42.6% of monitored days (116 out of 272) had good air quality in 2025.
What is the main pollutant in San Diego County? ▼
The primary pollutant in San Diego County is Ozone (O3), which was the main AQI driver on 178 days (65% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does San Diego County have? ▼
In 2025, San Diego County recorded 5 unhealthy air days (5 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 161.
Is the air quality in San Diego County getting better or worse? ▼
Air quality in San Diego County is improving based on 5-year trends (2020-2025). Best year: 2025 with 116 good days. Worst year: 2020 with 33 good days.
What does AQI 54 mean for health? ▼
San Diego County's median AQI of 54 falls in the "Moderate" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does San Diego County compare to other counties in California? ▼
San Diego County has 42.6% good air days. Nearby counties in California: Amador (84.8% good), Butte (66.1% good), Calaveras (73.9% good), Colusa (84.9% good), Del Norte (81.0% good), El Dorado (85.8% good).
What is the 90th percentile AQI in San Diego County? ▼
The 90th percentile AQI for San Diego County is 93, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 161 (Unhealthy).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir 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.