San Joaquin, California Air Quality Today
AirHistory tracks long-run EPA monitoring rather than live readings, so for the live number check AirNow.gov below. As a baseline, San Joaquin, California's most recent EPA year (2023) posted a median AQI of 47 (Good) against a 5-year median of 50 and an overall Grade of C. The dominant pollutant is Fine Particulate Matter (PM2.5), which tells you which days are most likely to spike.
Check Today's Live AQI in San Joaquin, California
AirHistory is built on 10 years of EPA Air Quality System records, so it shows you what air quality in San Joaquin, California typically looks like — not the live reading for this exact hour. For today's real-time AQI, check AirNow.gov (the EPA's official live index) or the AirNow Fire and Smoke Map during wildfire season.
That said, the history is the best predictor of a normal day. In 2023, San Joaquin, California posted a median AQI of 47 (Good), with 208 "Good" days and 9 days that crossed into "Unhealthy for Sensitive Groups" or worse. The dominant pollutant, Fine Particulate Matter (PM2.5), is the one most likely to push today's number up — Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
San Joaquin, California Air Quality Snapshot
| Air Quality Grade | C63/100 |
| 5-Year Median AQI | 50 (Moderate) |
| Most Recent Median AQI (2023) | 47 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Improving (-1.35 AQI/yr) |
| Unhealthy Days (last 5 yr) | 77 |
| National Rank (cleanest = #1) | #934 of 1,020 (92th most polluted percentile) |
| California Rank | #31 of 53 |
What Does the C Grade Mean?
San Joaquin, California earns a C — air quality is fair, but not great. With a 5-year median AQI of 50, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
San Joaquin, California's 5-year median AQI of 50 is 9 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within California, San Joaquin, California's air quality is roughly typical for the state, where the average city posts a 5-year median AQI of 49.
For context within California: Humboldt, California currently holds the state's cleanest grade (A, AQI 28), while Inyo, California sits at the bottom (F, AQI 57).
What's in San Joaquin, California's Air?
The dominant pollutant in San Joaquin, California is Fine Particulate Matter (PM2.5). Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Fine Particulate Matter (PM2.5) | 194 | 53% |
| Ground-Level Ozone | 161 | 44% |
| Coarse Particulate Matter (PM10) | 10 | 3% |
Is the Air Getting Better or Worse?
Air quality in San Joaquin, California has been improving over the past decade, with median AQI dropping by roughly 1.4 points per year. That is consistent with the broader national pattern — most U.S. metros have seen steady reductions in particulate and ozone pollution since the 2010s as cleaner vehicles and power plants come online.
In 2014, San Joaquin, California posted a median AQI of 58. By 2023 that figure was 47 — a drop of 11 AQI points cleaner across 10 years of EPA records.
Year-by-Year AQI in San Joaquin, California
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 58 | 112 | 34 | PM2.5 |
| 2015 | 60 | 83 | 36 | PM2.5 |
| 2016 | 60 | 62 | 26 | PM2.5 |
| 2017 | 55 | 141 | 33 | PM2.5 |
| 2018 | 59 | 91 | 33 | PM2.5 |
| 2019 | 47 | 202 | 12 | Ozone |
| 2020 | 54 | 162 | 31 | PM2.5 |
| 2021 | 55 | 140 | 16 | PM2.5 |
| 2022 | 48 | 192 | 9 | Ozone |
| 2023 | 47 | 208 | 9 | PM2.5 |
Health Context for San Joaquin, California
Across the past five years, this area has logged 77 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 15 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because PM2.5 penetrates deep into the lungs and bloodstream, an N95 or KN95 mask provides meaningful protection on smoky or high-particulate days — surgical masks do not.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
More about San Joaquin, California
San Joaquin, California has an Air Quality Grade of C (fair) with a 5-year median AQI of 50. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been improving over the past decade.
This answer pulls from the EPA Air Quality System (AQS), the authoritative federal source for U.S. air quality and pollution monitoring. The headline number above is the direct answer; what follows is the additional context most readers need to use the answer for a real decision rather than just a fact lookup.
A practical caveat: the headline answer above reflects the most recent the EPA Air Quality System (AQS) vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.
Source: EPA Outdoor Air Quality Data, 2026.