Air Quality in San Jose, California — Live
Live readings from PurpleAir sensors across San Jose — with free alerts the moment smoke moves in.
AQI 30 from 5 PurpleAir sensors · Trending up · data from PurpleAir
As of , the air quality in San Jose, California is AQI 30 — Good and rising — with PM2.5 at 5.4 µg/m³, the median of 5 live PurpleAir sensors reading 16 to 35. 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 Jose: 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 Jose and Santa Clara, Sunnyvale, Milpitas, Campbell. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in San Jose
The sensors Canairy reads in San Jose agree right now — all 5 sit in the Good band, a 19-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| City center | 26 | Good |
| 1.8 mi SSW | 28 | Good |
| 2.3 mi ESE | 35 | Good |
| 3.3 mi NE | 32 | Good |
| 6.1 mi WNW | 16 | Good |
Most days in San Jose the air is genuinely good, with clear skies and a northwesterly sea breeze off the bay. The trouble comes in two seasons: hot summer afternoons, when sun and trapped traffic exhaust cook up ozone in the Santa Clara Valley, and cold winter nights, when wood smoke and car exhaust settle under a temperature inversion. Wildfire smoke is the wild card that can overwhelm both.
What Canairy does for San Jose
A clear verdict
Not just a number — a plain-English call for San Jose: 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 Jose or across the country, on one screen.
What the air in San Jose is doing next
| When | AQI | Expected air quality | Main pollutant |
|---|---|---|---|
| Today | 44 | Good | PM2.5 |
| Tomorrow | 50 | Good | PM2.5 |
| Monday | 53 | Moderate | PM2.5 |
| Tuesday | — | Moderate | PM2.5 |
| Wednesday | — | Moderate | PM2.5 |
Forecast from EPA AirNow for the San Jose 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 valley is a bowl, and summer bakes it
San Jose sits at the south end of the Santa Clara Valley, ringed by hills to the east and west that block wind flow and hold air in place. Unlike San Francisco or the Peninsula, the city is far enough from the bay that cooling marine air usually doesn't reach it, so summer days run warm and still.
That combination is a recipe for ozone. On hot afternoons the valley's warmth and sun turn traffic exhaust into smog, and the surrounding mountains trap it in place. Air-district monitoring has recently found the Santa Clara Valley out-smogging every other Bay Area region, including the refinery corridor of the North Bay. Ozone is invisible, which is exactly why a live reading is worth having before an afternoon run or a kid's soccer practice.
Winter brings wood smoke and Spare the Air nights
When the weather turns cold and calm, San Jose's air problem flips from summer ozone to winter particle pollution. Cold nights, light winds and a temperature inversion trap smoke near the ground, and the Santa Clara Valley tends to take the worst of it. Wood smoke from fireplaces and stoves is the largest single source of the Bay Area's wintertime fine-particle pollution, more than a third of the total.
That's why the Bay Area Air Quality Management District issues Winter Spare the Air Alerts roughly twenty days a season, making it illegal to burn wood on those nights. The particles are small enough to reach deep into the lungs, and on a still valley night they can build up fast in a single neighborhood. Canairy's plain-English verdict tells you when it's a close-the-windows night rather than a light-a-fire one.
Wildfire smoke is the wild card
In August 2020, a freak lightning storm ignited the SCU and CZU Lightning Complex fires on either side of the South Bay. The SCU Complex alone burned nearly 394,000 acres and became one of the largest wildfires in California history. Smoke stalled over the valley for days.
San Jose air quality climbed into the 200s and 300s, hazardous territory, and the city set up clean air and cooling centers so residents had somewhere to escape the smoke. Fire smoke doesn't respect the valley's usual seasons or its geography; it can push the air from good to dangerous in a matter of hours, which is the case for watching a live sensor rather than yesterday's forecast.
San Jose air quality FAQ
What is the air quality in San Jose right now?
As of September 5, 2026 at 5:10 AM PDT, the air quality in San Jose, California is AQI 30 — Good — with PM2.5 at 5.4 µg/m³, the median of 5 live PurpleAir sensors. Open the windows. Great for outdoor activity.
When is San Jose's air usually worst?
There are two distinct seasons. Hot summer afternoons bring ozone, which the Santa Clara Valley's hills and heat trap in place from vehicle exhaust. Cold, still winter nights bring fine-particle pollution, mostly wood smoke, which is why the air district issues Winter Spare the Air Alerts and wood-burning bans about twenty times a season. Wildfire smoke can overwhelm either season.
Does wildfire smoke reach San Jose?
Yes. In August 2020 the SCU and CZU Lightning Complex fires filled the Santa Clara Valley with smoke, pushing San Jose's AQI into the 200s and 300s and forcing the city to open clean air centers. Fire smoke can raise the air from good to hazardous within hours, so a live sensor reading beats a day-old forecast during fire season.
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 Jose, 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 Jose
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