San Francisco Air Quality in 2021
In 2021, San Francisco's air quality (San Francisco-Oakland-Hayward, CA area) had a median daily AQI of 54 (Moderate) across 365 monitored days. 10 days (2.7%) reached Unhealthy for Sensitive Groups or worse, 139 were Good, and the year's peak AQI was 151 (Unhealthy). Fine particulate matter (PM2.5) set the daily AQI on 281 of those days. The cleanest month of 2021 was February (median AQI 44, 0 days above 100) and the worst was September (median 59, 3 days above 100, peak 129).
- Good: 38.1%
- Moderate: 59.2%
- Unhealthy for Sensitive Groups: 2.5%
- Unhealthy or worse: 0.3%
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How was San Francisco's air quality in 2021?
Moderate on a typical day: median AQI 54, with 10 days above AQI 100 out of 365 monitored — the 4th cleanest of 6 years on record for the area.
- ✓Peak AQI in 2021: 151 (Unhealthy).
- ✓Fine particulate matter (PM2.5) was the main pollutant on 281 days.
- ✓Cleanest month: February; worst: September.
Frequently asked questions
What was the average AQI in San Francisco in 2021?▾
EPA's Air Quality System puts San Francisco's (San Francisco-Oakland-Hayward, CA) median daily AQI for 2021 at 54, which is Moderate. 10 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 151.
Which month had the worst air quality in San Francisco in 2021?▾
The cleanest month of 2021 was February (median AQI 44, 0 days above 100) and the worst was September (median 59, 3 days above 100, peak 129).
Was 2021 a good or bad year for San Francisco's air?▾
Among the 6 years EPA has published for the area (2019–2024), 2021 ranks 4th cleanest by days above AQI 100. 2021's median of 54 is in line with the area's typical annual median of 53.
San Francisco month by month in 2021
San Francisco air quality month by month, 2021 (San Francisco-Oakland-Hayward, CA, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| January | 31 | 56 | 0 | 81 | PM2.5 |
| Februarycleanest | 28 | 44 | 0 | 62 | PM2.5 |
| March | 31 | 48 | 0 | 59 | PM2.5 |
| April | 30 | 58 | 0 | 84 | PM2.5 |
| May | 31 | 61 | 0 | 73 | PM2.5 |
| June | 30 | 45 | 2 | 151 | PM2.5 |
| July | 31 | 53 | 0 | 77 | PM2.5 |
| August | 31 | 60 | 3 | 150 | PM2.5 |
| Septemberworst | 30 | 59 | 3 | 129 | PM2.5 |
| October | 31 | 48 | 2 | 115 | PM2.5 |
| November | 30 | 59 | 0 | 77 | PM2.5 |
| December | 31 | 49 | 0 | 92 | PM2.5 |
How 2021 compares
Among the 6 years EPA has published for the area (2019–2024), 2021 ranks 4th cleanest by days above AQI 100.
2021's median of 54 is in line with the area's typical annual median of 53.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in San Francisco
The latest EPA AirNow observation puts San Francisco's AQI at 28 (PM2.5). The figures above are multi-year annual statistics, not today's reading.
View current San Francisco air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (San Francisco-Oakland-Hayward, CA), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.