San Francisco Air Quality in October
Across 2019–2025, San Francisco's October air quality had a median AQI of 54 (Moderate) over 195 monitored days in the San Francisco-Oakland-Hayward, CA area. 3.1% of October days (6 of 195) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 80.0% of days. The cleanest October on record here was 2024 (median AQI 52, 0 days above 100) and the worst was 2020 (median 59, 3 days above 100, peak AQI 185).
- Good: 33.3%
- Moderate: 63.6%
- Unhealthy for Sensitive Groups: 2.1%
- Unhealthy or worse: 1.0%
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How is the air in San Francisco in October?
Moderate on a typical day: median AQI 54 across 2019–2025, with 3.1% of October days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓33.3% of October days were Good (AQI 0–50), 63.6% Moderate (51–100).
- ✓6 days of 195 reached AQI 101+; the October peak was 185.
- ✓Best October: 2024; worst October: 2020.
Frequently asked questions
What is the air quality like in San Francisco in October?▾
Across 2019–2025, the median daily AQI in San Francisco in October was 54 (Moderate). 33.3% of days were Good, 63.6% Moderate, and 3.1% reached Unhealthy for Sensitive Groups or worse, based on 195 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in San Francisco?▾
A typical October day in San Francisco is Moderate (median AQI 54): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 32 of October days (3.1%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes San Francisco's October air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 80.0% of October days in San Francisco. The highest October AQI recorded in 2019–2025 was 185 (Unhealthy), in 2020.
San Francisco October air quality, year by year
San Francisco October air quality by year (San Francisco-Oakland-Hayward, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 57 | 1 | 102 | PM2.5 |
| 2020worst | 31 | 59 | 3 | 185 | PM2.5 |
| 2021 | 31 | 48 | 2 | 115 | PM2.5 |
| 2022 | 31 | 57 | 0 | 77 | PM2.5 |
| 2023 | 31 | 53 | 0 | 93 | PM2.5 |
| 2024cleanest | 31 | 52 | 0 | 82 | PM2.5 |
| 2025 | 9 | 20 | 0 | 41 | PM2.5 |
What October air means in San Francisco
A typical October day in San Francisco is Moderate (median AQI 54): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 32 of October days (3.1%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
October's median AQI of 54 is in line with San Francisco's whole-year median of 53, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so San Francisco runs above the national October norm; 3.1% of its October days topped AQI 100 versus 1.3% nationally (above average).
October is part of San Francisco's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in San Francisco
The latest EPA AirNow observation puts San Francisco's AQI at 36 (PM2.5). The figures above are multi-year month 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.