What Is the Air Quality in Santa Clara, California?
Santa Clara, California has an Air Quality Grade of C (fair) with a 5-year median AQI of 49. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
Santa Clara, California Air Quality Snapshot
| Air Quality Grade | C59/100 |
| 5-Year Median AQI | 49 (Good) |
| Most Recent Median AQI (2023) | 43 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Stable (-0.19 AQI/yr) |
| Unhealthy Days (last 5 yr) | 40 |
| National Rank (cleanest = #1) | #910 of 1,020 (89th most polluted percentile) |
| California Rank | #30 of 53 |
What Does the C Grade Mean?
Santa Clara, California earns a C — air quality is fair, but not great. With a 5-year median AQI of 49, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Santa Clara, California's 5-year median AQI of 49 is 8 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within California, Santa Clara, 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 Santa Clara, California's Air?
The dominant pollutant in Santa Clara, 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 | 184 | 50% |
| Fine Particulate Matter (PM2.5) | 179 | 49% |
| Nitrogen Dioxide | 2 | 1% |
Is the Air Getting Better or Worse?
Air quality in Santa Clara, California has held roughly steady over the past decade, with year-to-year shifts in median AQI of less than half a point. That stability makes the city's long-run grade a reliable signal of what residents can expect day-to-day.
In 2014, Santa Clara, California posted a median AQI of 46. By 2023 that figure was 43 — a drop of 3 AQI points cleaner across 10 years of EPA records.
Year-by-Year AQI in Santa Clara, California
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 46 | 216 | 8 | PM2.5 |
| 2015 | 51 | 179 | 7 | PM2.5 |
| 2016 | 50 | 187 | 1 | PM2.5 |
| 2017 | 52 | 174 | 12 | PM2.5 |
| 2018 | 53 | 154 | 17 | PM2.5 |
| 2019 | 48 | 205 | 4 | PM2.5 |
| 2020 | 52 | 174 | 20 | PM2.5 |
| 2021 | 53 | 147 | 7 | PM2.5 |
| 2022 | 49 | 188 | 5 | PM2.5 |
| 2023 | 43 | 240 | 4 | Ozone |
Health Context for Santa Clara, California
Across the past five years, this area has logged 40 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 8 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.
Santa Clara, California has an Air Quality Grade of C (fair) with a 5-year median AQI of 49. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
The data source behind this answer is the EPA Air Quality System (AQS). Every figure on the page traces back to that source; the methodology page describes the inputs and the refresh cadence in full detail.
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.