San Francisco Air Quality in 2020
In 2020, San Francisco's air quality (San Francisco-Oakland-Hayward, CA area) had a median daily AQI of 53 (Moderate) across 366 monitored days. 22 days (6.0%) reached Unhealthy for Sensitive Groups or worse, 150 were Good, and the year's peak AQI was 243 (Very Unhealthy). Fine particulate matter (PM2.5) set the daily AQI on 286 of those days. The cleanest month of 2020 was March (median AQI 40, 0 days above 100) and the worst was September (median 88, 11 days above 100, peak 243).
- Good: 41.0%
- Moderate: 53.0%
- Unhealthy for Sensitive Groups: 2.5%
- Unhealthy or worse: 3.6%
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How was San Francisco's air quality in 2020?
Moderate on a typical day: median AQI 53, with 22 days above AQI 100 out of 366 monitored — the 6th cleanest of 6 years on record for the area.
- ✓Peak AQI in 2020: 243 (Very Unhealthy).
- ✓Fine particulate matter (PM2.5) was the main pollutant on 286 days.
- ✓Cleanest month: March; worst: September.
Frequently asked questions
What was the average AQI in San Francisco in 2020?▾
EPA's Air Quality System puts San Francisco's (San Francisco-Oakland-Hayward, CA) median daily AQI for 2020 at 53, which is Moderate. 22 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 243.
Which month had the worst air quality in San Francisco in 2020?▾
The cleanest month of 2020 was March (median AQI 40, 0 days above 100) and the worst was September (median 88, 11 days above 100, peak 243).
Was 2020 a good or bad year for San Francisco's air?▾
Among the 6 years EPA has published for the area (2019–2024), 2020 ranks 6th cleanest by days above AQI 100 — the worst year on record here. 2020's median of 53 is in line with the area's typical annual median of 53.
San Francisco month by month in 2020
San Francisco air quality month by month, 2020 (San Francisco-Oakland-Hayward, CA, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| January | 31 | 52 | 0 | 77 | PM2.5 |
| February | 29 | 55 | 0 | 71 | PM2.5 |
| Marchcleanest | 31 | 40 | 0 | 65 | PM2.5 |
| April | 30 | 43 | 0 | 61 | PM2.5 |
| May | 31 | 48 | 0 | 93 | PM2.5 |
| June | 30 | 48 | 0 | 71 | PM2.5 |
| July | 31 | 53 | 1 | 115 | PM2.5 |
| August | 31 | 64 | 7 | 182 | PM2.5 |
| Septemberworst | 30 | 88 | 11 | 243 | PM2.5 |
| October | 31 | 59 | 3 | 185 | PM2.5 |
| November | 30 | 54 | 0 | 85 | PM2.5 |
| December | 31 | 60 | 0 | 100 | PM2.5 |
How 2020 compares
Among the 6 years EPA has published for the area (2019–2024), 2020 ranks 6th cleanest by days above AQI 100 — the worst year on record here.
2020's median of 53 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.