What Is the Air Quality in Stanislaus, California?
Stanislaus, California has an Air Quality Grade of D (poor) with a 5-year median AQI of 57. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been improving over the past decade.
Stanislaus, California Air Quality Snapshot
| Air Quality Grade | D46/100 |
| 5-Year Median AQI | 57 (Moderate) |
| Most Recent Median AQI (2023) | 54 (Moderate) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Improving (-0.54 AQI/yr) |
| Unhealthy Days (last 5 yr) | 153 |
| National Rank (cleanest = #1) | #1000 of 1,020 (98th most polluted percentile) |
| California Rank | #44 of 53 |
What Does the D Grade Mean?
Stanislaus, California earns a D — air quality falls below the U.S. average, with a 5-year median AQI of 57. Residents with asthma, COPD, heart disease, or young children should watch daily AQI forecasts and limit outdoor exertion when alerts go out.
Stanislaus, California's 5-year median AQI of 57 is 16 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within California, Stanislaus, California runs more polluted than the state average of 49 — local sources or geography are concentrating pollution above the state's typical reading.
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 Stanislaus, California's Air?
The dominant pollutant in Stanislaus, 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 |
|---|---|---|
| Ground-Level Ozone | 199 | 55% |
| Fine Particulate Matter (PM2.5) | 161 | 44% |
| Coarse Particulate Matter (PM10) | 5 | 1% |
Is the Air Getting Better or Worse?
Air quality in Stanislaus, California has been improving over the past decade, with median AQI dropping by roughly 0.5 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, Stanislaus, California posted a median AQI of 60. By 2023 that figure was 54 — a drop of 6 AQI points cleaner across 10 years of EPA records.
Year-by-Year AQI in Stanislaus, California
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 60 | 112 | 59 | Ozone |
| 2015 | 62 | 92 | 48 | PM2.5 |
| 2016 | 59 | 102 | 43 | PM2.5 |
| 2017 | 61 | 127 | 63 | Ozone |
| 2018 | 59 | 109 | 47 | PM2.5 |
| 2019 | 52 | 168 | 23 | Ozone |
| 2020 | 60 | 131 | 37 | PM2.5 |
| 2021 | 61 | 84 | 47 | PM2.5 |
| 2022 | 57 | 108 | 23 | PM2.5 |
| 2023 | 54 | 166 | 23 | Ozone |
Health Context for Stanislaus, California
Across the past five years, this area has logged 153 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 31 days per year, or roughly one every five to seven days. That is well above the national norm and explains the D grade.
Treat daily AQI forecasts as essential input. On flagged days, sensitive groups (asthma, COPD, heart disease, pregnancy, young children, older adults) should limit outdoor exertion and keep windows closed. A HEPA air cleaner sized to a bedroom or family room can cut indoor PM2.5 by 80%+ during smoke or pollution events. 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.
Stanislaus, California has an Air Quality Grade of D (poor) with a 5-year median AQI of 57. 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.
For readers turning this answer into action: cross-reference against the underlying the EPA Air Quality System (AQS) record before acting on time-sensitive decisions. The site renders the data as it was published; subsequent revisions can shift the picture, and the live federal data is always the authoritative current reference.
Source: EPA Outdoor Air Quality Data, 2026.