Median AQI
44
Good
California · County air quality · 2025
San Joaquin County, California
Median AQI 44 (Good). 65.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 65.9%
- Good-air days
- 0
- Unhealthy days
- 24%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, San Joaquin County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 44 with 65.9% of 182 monitored days in the Good band, driven mainly by PM2.5.
- 44
- median AQI · Good
- 65.9%
- days rated Good
- PM2.5
- main pollutant
- 24%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 93.
Data updated July 2026
- Good · 120 d · 65.9%
- Moderate · 62 d · 34.1%
How did San Joaquin County's air break down in 2025?
Across 182 monitored days, 120 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 93 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 182 days monitored. Median AQI: 44 (Good).
Insights: San Joaquin County, California. EPA monitors recorded a median Air Quality Index of 44 across 182 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 120 (66%) fell in the Good band (AQI 0–50), 62 (34%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 67, while the worst single-day peak hit 93 (Moderate). Residents averaged about 19.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (105 days), Ozone (77 days). Across the 2020–2025 trend window, good days shifted by -42 and the median AQI moved -10 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 93, moderate but never Unhealthy. 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
65.9%
120 of 182 monitored days
-9.1pp vs 75% target
Max AQI Recorded
93
Moderate
Health Grade
Moderate
90th-pct AQI 67
San Joaquin County, Good days share 65.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
San Joaquin County, Unhealthy-or-worse share 0.0%
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 182 monitored days across EPA AQI categories.
Good
120
66%
Moderate
62
34%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in San Joaquin County.
- PM2.5 · 105 days · 57.7%
- Ozone · 77 days · 42.3%
Health Impact Assessment
Moderate
San Joaquin County's air quality is rated Moderate based on 65.9% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 65.9% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 105 of 182 monitored days.
5-Year Air Quality Trend
Air quality is improving in San Joaquin County. Best year: 2023 (208 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 162 | 173 | 16 | 13 | 54 | 215 |
| 2021 | 140 | 209 | 15 | 1 | 55 | 153 |
| 2022 | 192 | 164 | 8 | 0 | 48 | 208 |
| 2023 | 208 | 148 | 9 | 0 | 47 | 119 |
| 2024 | 178 | 177 | 11 | 0 | 51 | 140 |
| 2025 | 120 | 62 | 0 | 0 | 44 | 93 |
How does San Joaquin County compare?
How San Joaquin County compares
Good-day share worse than US avg
San Joaquin County 65.9%
Amador County, California 84.8%
US average 76.5%
Median AQI worse than US avg
San Joaquin County 44
Amador County, California 40
US average 38
Unhealthy days / yr about average
San Joaquin County 0
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 Joaquin County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What San Joaquin County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 44 means for exposure. Health guidance
- See how San Joaquin County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare San Joaquin County with its California neighbours before drawing a conclusion about the region. All of California
Based on 182 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 Joaquin County, California? ▼
San Joaquin County has a median Air Quality Index (AQI) of 44, rated "Good." 65.9% of monitored days (120 out of 182) had good air quality in 2025.
What is the main pollutant in San Joaquin County? ▼
The primary pollutant in San Joaquin County is Fine Particles (PM2.5), which was the main AQI driver on 105 days (58% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does San Joaquin County have? ▼
In 2025, San Joaquin County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 93.
Is the air quality in San Joaquin County getting better or worse? ▼
Air quality in San Joaquin County is improving based on 5-year trends (2020-2025). Best year: 2023 with 208 good days. Worst year: 2025 with 120 good days.
What does AQI 44 mean for health? ▼
San Joaquin County's median AQI of 44 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does San Joaquin County compare to other counties in California? ▼
San Joaquin County has 65.9% 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 Joaquin County? ▼
The 90th percentile AQI for San Joaquin County is 67, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 93 (Moderate).
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.