Air Quality in San Francisco, California — Live
Live readings from PurpleAir sensors across San Francisco — with free alerts the moment smoke moves in.
AQI 31 from 5 PurpleAir sensors · Trending up · data from PurpleAir
As of , the air quality in San Francisco, California is AQI 31 — Good and rising — with PM2.5 at 5.6 µg/m³, the median of 5 live PurpleAir sensors reading 7 to 34. Canairy's verdict: Breathe easy.
For scale, that PM2.5 reading is below the World Health Organization's 24-hour guideline of 15 µg/m³. The WHO figure is a daily average and this is a live reading, so read it as a sense of magnitude rather than a formal exceedance — a brief spike and a bad day are not the same thing. More on the WHO guidelines
Pollen today in San Francisco: weeds pollen is the strongest of the three at a low level, from Google's pollen forecast. Canairy shows the tree, grass and weed forecast beside the air reading on every plan, including the free one.
Free to download · Live data from PurpleAir & public monitors
Live PurpleAir sensor map for San Francisco and Daly City, South San Francisco, Sausalito, Berkeley. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in San Francisco
The sensors Canairy reads in San Francisco agree right now — all 5 sit in the Good band, a 27-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| 2.0 mi SW | 7 | Good |
| 2.2 mi SSE | 31 | Good |
| 3.1 mi SSW | 29 | Good |
| 3.3 mi SW | 31 | Good |
| 3.9 mi WSW | 34 | Good |
San Francisco has some of the cleanest big-city air in the country most of the year, because the same cold ocean and sea breeze that make the fog also flush the city's air out toward the Pacific every afternoon. The exceptions are the days that stick in memory: wildfire smoke drifting in from fires burning hundreds of miles away, and cold, still winter nights when wood smoke settles into the neighborhoods.
What Canairy does for San Francisco
A clear verdict
Not just a number — a plain-English call for San Francisco: open the windows, or keep them shut.
Smoke alerts
A push or text the moment the air crosses your threshold — and again when it clears.
A heads-up before it's bad
Trend alerts catch the air turning, so you can close up the house before the smoke settles in.
Every place you care about
Home, work, the kids' school — across San Francisco or across the country, on one screen.
What the air in San Francisco is doing next
| When | AQI | Expected air quality | Main pollutant |
|---|---|---|---|
| Today | 44 | Good | PM2.5 |
| Tomorrow | 53 | Moderate | PM2.5 |
| Monday | 55 | Moderate | PM2.5 |
| Tuesday | — | Moderate | PM2.5 |
| Wednesday | — | Moderate | PM2.5 |
Forecast from EPA AirNow for the San Francisco reporting area. Canairy watches the live sensors against it and tells you when the air actually crosses your threshold, rather than leaving you to check.
The fog and the sea breeze are the city's air filter
San Francisco's air is clean most of the time for a reason that has nothing to do with luck. Cold water off the coast cools the air above it into the marine layer, and that ocean air pours in through the Golden Gate on the afternoon sea breeze. On an ordinary day it keeps moving through the city and out the other side, carrying traffic exhaust and everyday pollution with it before anything has a chance to build up.
The trouble starts when that airflow stops. When a hot, dry offshore Diablo wind pushes down from the interior, it shuts off the cooling sea breeze, dries out the hills and sets up the region's worst fire weather. Those are the same conditions that let smoke settle in and stay, which is why the Bay Area's rare bad-air days almost always line up with the days the ocean breeze goes quiet.
The smoke years locals still talk about
The 2018 Camp Fire, burning in Butte County more than 150 miles away, buried the Bay Area in smoke for nearly two straight weeks from November 8 to 20, the worst stretch on record since the air district began tracking in 1999. San Francisco's index climbed to around 239, deep into the very unhealthy range, and a district forecaster said the readings were the kind you would normally see in India or China rather than coastal California.
Then came September 9, 2020, the orange sky day, when smoke from the North Complex Fire and more than twenty other blazes turned the sky an eerie Mars-like orange and streetlights flicked on at midday. Oddly, the ground-level air that day was not as dangerous as it looked, because the marine layer held most of the smoke high overhead. It was a vivid reminder that in San Francisco the smoke is almost always someone else's fire arriving on the wind, not a fire in the city itself.
Winter wood smoke and the freeway neighborhoods
Wildfires get the headlines, but the pollution San Francisco makes for itself shows up in winter. On cold, still nights, smoke from home fireplaces and wood stoves settles into the streets and becomes the single largest source of fine-particle pollution in the Bay Area, more than a third of the total. That is why the air district calls Spare the Air alerts and bans all wood burning on the worst nights, and in late 2025 it lowered the level that triggers those bans so the alerts come before the smoke piles up.
The burden is not shared evenly across the city. Southeast neighborhoods like Bayview-Hunters Point sit between US-101 and I-280, the Port of San Francisco and decades of diesel truck traffic, and carry the heaviest pollution load in San Francisco. It is the clearest local example of why a single citywide number is never the whole story, and why a sensor near your own block tells you more than the airport reading a few miles away.
San Francisco air quality FAQ
What is the air quality in San Francisco right now?
As of September 5, 2026 at 5:10 AM PDT, the air quality in San Francisco, California is AQI 31 — Good — with PM2.5 at 5.6 µg/m³, the median of 5 live PurpleAir sensors. Open the windows. Great for outdoor activity.
Why is San Francisco's air usually so clean?
The cold Pacific and the afternoon sea breeze act like a filter. Ocean air pours in through the Golden Gate and keeps moving through the city, carrying everyday traffic and pollution out toward the coast before it can build up. Air quality tends to slip only when that sea breeze stops, which is usually during hot offshore Diablo wind events or when wildfire smoke drifts in from fires elsewhere in the state.
Does wildfire smoke actually reach San Francisco?
Yes, though it is almost always smoke from fires burning far away rather than fires in the city itself. The 2018 Camp Fire, more than 150 miles off in Butte County, pushed San Francisco's index to around 239 and blanketed the Bay Area for nearly two weeks, the worst stretch on record. On the orange sky day of September 9, 2020, smoke from Northern California fires turned the sky dark orange, though the marine layer that day held most of it high overhead so ground-level air was less severe than it appeared.
What the AQI numbers mean
| AQI | Category | What it means for you |
|---|---|---|
| 0–50 | Good | Open the windows. Great for outdoor activity. |
| 51–100 | Moderate | Sensitive groups may want to take it slower outside. |
| 101–150 | Unhealthy for Sensitive Groups | Kids, elderly, and respiratory conditions stay closer to home. |
| 151–200 | Unhealthy | Skip outdoor exercise. Close windows. |
| 201–300 | Very Unhealthy | Limit time outside. N95 if you must go. |
| 301+ | Hazardous | Health emergency. Stay inside, run filtration if you have it. |
Canairy lets you tighten these bands if you’re more sensitive than the EPA default, so an alert can fire before the official category changes. How to read the Air Quality Index
Where these readings come from
The AQI at the top of this page is the median of the 5 curated PurpleAir sensors Canairy tracks in and around San Francisco, with outliers set aside so that one sensor brought indoors — or parked beside a barbecue — cannot set the number for a whole city. Every sensor behind it is listed above with its distance and bearing from the city center. There is no black box here.
In the app, a place you save resolves the same way first. When no neighborhood sensor is reporting it falls back to the nearest EPA AirNow monitor, and anything modeled rather than measured is labelled a regional estimate rather than passed off as a sensor reading. How low-cost sensors compare to regulatory monitors
About Canairy
Canairy is free to download. The free plan covers one saved place with live readings, a plain-English verdict, and push alerts when the air crosses a threshold you choose. Paid plans add more places, faster refreshes, and SMS alerts. It is built by two parents in Sonoma County, California, who got tired of guessing whether it was safe to send the kids outside. Why we built it
Go deeper
Air quality near San Francisco
We watch San Francisco's air. You live your life.
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