San Mateo, California Air Quality
San Mateo County, California (CA)
↓ Improvingover 10 years
10-Year AQI Trend
The solid line shows the median AQI each year. The dashed line shows the 90th percentile (worst 10% of days). This area has seen measurable air quality improvement over the decade.
Air Quality Day Breakdown
Number of days per year in each EPA AQI category. Green = Good (AQI 0-50), Yellow = Moderate (51-100), Orange = Unhealthy for Sensitive Groups (101-150), Red = Unhealthy or worse (151+).
Year-by-Year Data
| Year | Median AQI | 90th Pct | Max AQI | Good Days | Moderate | Unhealthy+ | Pollutant |
|---|---|---|---|---|---|---|---|
| 2023 | 31 | 41 | 71 | 355 | 8 | 0 | Ozone |
| 2022 | 36 | 60 | 85 | 267 | 98 | 0 | Ozone |
| 2021 | 36 | 56 | 90 | 290 | 75 | 0 | Ozone |
| 2020 | 37 | 64 | 199 | 257 | 99 | 10 | PM2.5 |
| 2019 | 39 | 57 | 122 | 276 | 87 | 2 | PM2.5 |
| 2018 | 42 | 61 | 197 | 236 | 116 | 13 | PM2.5 |
| 2017 | 42 | 62 | 155 | 238 | 120 | 7 | PM2.5 |
| 2016 | 47 | 59 | 70 | 214 | 152 | 0 | PM2.5 |
| 2015 | 35 | 56 | 101 | 297 | 67 | 1 | Ozone |
| 2014 | 38 | 59 | 99 | 278 | 87 | 0 | PM2.5 |
What This Means for San Mateo County Residents
San Mateo, California has received an Air Quality Grade of B (72/100) based on a decade of EPA monitoring data. The current median AQI of 31 falls in the "Good" range.
Encouragingly, air quality here has been improving, with the median AQI dropping by 7 points over the monitoring period. This trend suggests continued investment in emission controls and cleaner energy.
The primary pollutant affecting this area is Fine Particulate Matter (PM2.5). Over the past 5 years, this area has averaged 2 unhealthy air quality days per year — days when sensitive groups (children, elderly, those with respiratory conditions) should limit outdoor activity.