Median AQI
46
Good
California · County air quality · 2025
San Joaquin County, California
Median AQI 46 (Good). 60.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 46
- Median AQI
- 60.0%
- Good-air days
- 0
- Unhealthy days
- 15%
- Cleaner than US counties
San Joaquin County's 2025 annual median AQI is 46 (Good), with 60.0% Good days
According to the U.S. EPA Air Quality System, San Joaquin County, California posted a 2025 median AQI of 46 (Good) across 365 monitored days, with 60.0% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- San Joaquin County's 60.0% Good-day share places it cleaner than 15% of US counties in 2025.
- Closest median-AQI peer
- Beaver County (55.6% Good, median AQI 46) is the closest nationwide median-AQI peer to San Joaquin County.
- 2020–2025 trend
- San Joaquin County's floor-qualifying Good-day share is improving from 2020 to 2025 (44.5% → 60.0%).
- Median AQI
- Median AQI: 46
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 46 with 60.0% of 365 monitored days in the Good band, driven mainly by PM2.5.
- 46
- median AQI · Good
- 60.0%
- days rated Good
- PM2.5
- main pollutant
- 15%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 93.
Annual release change
What changed in the 2025 EPA annual release
- San Joaquin County's Good-day share rose from 48.6% to 60.0% between the 2024 and 2025 EPA annual releases, a change of +11.4 percentage points.
- San Joaquin County's peak single-day AQI fell from 140 to 93 between the 2024 and 2025 EPA annual releases, a change of -47 points.
- San Joaquin County's median AQI fell from 51 to 46 between the 2024 and 2025 EPA annual releases, a change of -5 points.
Data updated August 2026
- Good · 219 d · 60.0%
- Moderate · 146 d · 40.0%
How did San Joaquin County's air break down in 2025?
Across 365 monitored days, 219 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). 365 days monitored. Median AQI: 46 (Good).
Insights: San Joaquin County, California. EPA monitors recorded a median Air Quality Index of 46 across 365 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 219 (60%) fell in the Good band (AQI 0–50), 146 (40%) 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 18.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (196 days), Ozone (163 days), PM10 (6 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +15.7 points and the median AQI moved -8 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: Alameda (53.0% good, AQI 49); Amador (87.4% good, AQI 38); Butte (65.2% good, AQI 46); Calaveras (82.2% good, AQI 40); Colusa (79.2% good, AQI 40); Contra Costa (53.5% good, AQI 48).
Air Quality Summary
Good Days
60.0%
219 of 365 monitored days
-15.0pp vs 75% target
Max AQI Recorded
93
Moderate
Health Grade
Moderate
90th-pct AQI 67
San Joaquin County, Good days share 60.0%
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 365 monitored days across EPA AQI categories.
Good
219
60%
Moderate
146
40%
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 · 196 days · 53.7%
- Ozone · 163 days · 44.7%
- PM10 · 6 days · 1.6%
Health Impact Assessment
Moderate
San Joaquin County's air quality is rated Moderate based on 60.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 60.0% of monitored days in 2025, with a median AQI of 46. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 196 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in San Joaquin County. Highest Good-day share: 2025 (60.0%, 219 of 365 monitored 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 | 219 | 146 | 0 | 0 | 46 | 93 |
How does San Joaquin County compare?
How San Joaquin County compares
Good-day share worse than typical
San Joaquin County 60.0%
Beaver County, Pennsylvania 55.6%
Typical US county 76.0%
Median AQI worse than typical
San Joaquin County 46
Beaver County, Pennsylvania 46
Typical US county 39
Unhealthy days / yr better than typical
San Joaquin County 0
Beaver County, Pennsylvania 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as San Joaquin County (46), not geographic neighbors.
Beaver County, Pennsylvania
Median AQI 46 · 55.6% Good-day share
Brookings County, South Dakota
Median AQI 46 · 58.6% Good-day share
Buchanan County, Missouri
Median AQI 46 · 56.4% Good-day share
Butte County, California
Median AQI 46 · 65.2% Good-day share
Clark County, Indiana
Median AQI 46 · 58.1% Good-day share
Clarke County, Georgia
Median AQI 46 · 57.8% Good-day share
Same primary pollutant: PM2.5
PM2.5 led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Allen County, Indiana
60.0% Good-day share · median AQI 44
Holmes County, Florida
60.0% Good-day share · median AQI 46
Peoria County, Illinois
59.9% Good-day share · median AQI 45
Orange County, Texas
60.2% Good-day share · median AQI 45
Hamilton County, Florida
60.2% Good-day share · median AQI 46
Montgomery County, Ohio
60.3% Good-day share · median AQI 46
California counties on the map
Geographic containment only, other monitored counties in California, independent of AQI or pollutant match.
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 46 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 365 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in San Joaquin County, California? ▼
San Joaquin County has a median Air Quality Index (AQI) of 46, rated "Good." 60.0% of monitored days (219 out of 365) 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 196 days (54% 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 across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 60.0% (219 of 365 days). Lowest qualifying Good-day share: 2021 at 38.4% (140 of 365 days).
What does AQI 46 mean for health? ▼
San Joaquin County's median AQI of 46 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does San Joaquin County compare to other counties in California? ▼
San Joaquin County has 60.0% good air days. Nearby counties in California: Alameda (53.0% good), Amador (87.4% good), Butte (65.2% good), Calaveras (82.2% good), Colusa (79.2% good), Contra Costa (53.5% 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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for San Joaquin County, California · 2020–2025
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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.