San Francisco Air Quality in January
Across 2019–2025, San Francisco's January air quality had a median AQI of 53 (Moderate) over 197 monitored days in the San Francisco-Oakland-Hayward, CA area. 0.0% of January days (0 of 197) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 88.8% of days. The cleanest January on record here was 2025 (median AQI 21, 0 days above 100) and the worst was 2022 (median 60, 0 days above 100, peak AQI 86).
- Good: 41.6%
- Moderate: 58.4%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
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How is the air in San Francisco in January?
Moderate on a typical day: median AQI 53 across 2019–2025, with 0.0% of January days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓41.6% of January days were Good (AQI 0–50), 58.4% Moderate (51–100).
- ✓0 days of 197 reached AQI 101+; the January peak was 89.
- ✓Best January: 2025; worst January: 2022.
Frequently asked questions
What is the air quality like in San Francisco in January?▾
Across 2019–2025, the median daily AQI in San Francisco in January was 53 (Moderate). 41.6% of days were Good, 58.4% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 197 monitored days in EPA's Air Quality System.
Is January a good time for outdoor exercise in San Francisco?▾
A typical January day in San Francisco is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of January days 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 January air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 88.8% of January days in San Francisco. The highest January AQI recorded in 2019–2025 was 89 (Moderate), in 2022.
San Francisco January air quality, year by year
San Francisco January 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 | 56 | 0 | 89 | PM2.5 |
| 2020 | 31 | 52 | 0 | 77 | PM2.5 |
| 2021 | 31 | 56 | 0 | 81 | PM2.5 |
| 2022worst | 31 | 60 | 0 | 86 | PM2.5 |
| 2023 | 31 | 44 | 0 | 62 | PM2.5 |
| 2024 | 31 | 55 | 0 | 75 | PM2.5 |
| 2025cleanest | 11 | 21 | 0 | 32 | PM2.5 |
What January air means in San Francisco
A typical January day in San Francisco is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of January days reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
January's median AQI of 53 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 January AQI across every EPA metro area (95,602 metro-days, 2019–2025) is 39, so San Francisco runs above the national January norm; 0.0% of its January days topped AQI 100 versus 0.7% nationally (about the same).
January is part of San Francisco's winter season (December, January, February); the winter 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.