San Francisco, CA Air Quality Index (AQI)
Real-time air quality for San Francisco (873,965 residents). We show AirNow's AQI with its source and timestamp, plus a NowCast trend, the local forecast, and any active air-quality alerts. Peak smoke risk here runs mid-summer into fall, when Western wildfires and long-range plumes settle into the valleys.
About air quality in San Francisco
San Francisco is the 4th most populous of the 10 California cities we track, with a population of about 873,965, in San Francisco County.
A city this size carries its own year-round PM2.5 baseline from traffic, construction and industry, so wildfire smoke here arrives on top of an existing load rather than against clean background air. That matters for reading the number: a moderate AQI in San Francisco on a smoke-free week is normal, and the same AQI during a plume means considerably more smoke than it would somewhere with a lower floor.
Smoke risk here concentrates in September through December, driven by Santa Ana wind events pushing fire and smoke toward the coast, which is why the worst days here can fall late in the year. Outside that window an elevated reading in San Francisco is more likely to be local — traffic, dust, or a temperature inversion holding everyday pollution near the ground — than wildfire smoke, and the dominant pollutant shown above is what tells the two apart.
How local is this reading? The AQI above is reported for a monitoring area, not for a street address. The nearest city we track is Oakland, CA, about 8 miles away — close enough that the two usually move together, so a large gap between them is a sign the plume edge is somewhere between you.
Today & tomorrow
What each level means
| AQI | Level | What to do |
|---|---|---|
| 0–50 | Good | A great day to be active outside. |
| 51–100 | Moderate | Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors and watch for symptoms. |
| 101–150 | Unhealthy for Sensitive Groups | Sensitive groups should reduce prolonged or heavy exertion outdoors, take more breaks, and reschedule strenuous activities. |
| 151–200 | Unhealthy | Everyone should reduce prolonged or heavy exertion outdoors; sensitive groups should move activities indoors or reschedule. |
| 201–300 | Very Unhealthy | Everyone should avoid prolonged or heavy exertion and move activities indoors; sensitive groups should stay indoors and keep activity low. |
| 301–500 | Hazardous | Everyone should avoid all physical activity outdoors; stay indoors with clean air and keep activity low. |
Guidance paraphrased from EPA. Not medical advice — see disclaimer.
Nearby cities
All California cities · Smoke & your health · Can I go outside?
San Francisco air quality FAQ
What is the air quality in San Francisco right now?
The live AQI for San Francisco, CA is shown at the top of this page, sourced from AirNow (U.S. EPA) and computed with the 2024 EPA standard, with the observation time and source labeled.
Is it safe to go outside in San Francisco today?
It depends on the current AQI and whether you're in a sensitive group. At AQI 101–150 sensitive groups should cut back on prolonged outdoor exertion; at 151+ everyone should. Use our "Can I go outside?" tool for tailored guidance.
Why does San Francisco's AQI here match AirNow?
Because AirNow is our display truth for US monitors — we show its reported number, never a self-computed value that disagrees with it for the same monitor.
When is wildfire smoke worst in California?
In the West, smoke risk peaks mid-summer through fall during active fire season and can linger in valleys.