Right now: San Jose is at 51, moderate.
Is the air safe to breathe in San Jose today?
In San Jose, BreatheCheck reads 51 as Go. The cutoffs: go below 101, keep it short and easy from 101 to 150, move it indoors above 150. These are our own thresholds, drawn on the EPA bands — EPA itself classifies 101–150 as Unhealthy for Sensitive Groups and does not tell you how long to stay out.
Go AQI 0–100
Normal outdoor plans. No change needed.
Short & unloaded AQI 101–150
A 20-minute dog walk, not a 2.5-hour run. Keep it brief and easy.
Don’t go AQI 151+
Move it indoors. Above 200 that becomes everyone, not just sensitive groups.
Above 200 this stops being a personal call: everyone indoors.
Duration and intensity are two separate dials
| Under 20 min | 20–60 min | Over an hour | |
|---|---|---|---|
| Easy | Go | Go | Go |
| Moderate | Go | Go | Go |
| Hard | Go | Go | Go |
Go Every combination lands the same way at this reading — a hard hour is no different from an easy twenty minutes. The two dials separate above 80.
Where people actually draw the line
All the thresholds people reported, and who reported them
- 60 Asthmatic runnerone runner’s own 156-run log
- 75–100 Daycare / schoolparents and staff in one r/toddlers thread, Aug 2025 — not a published rule
- 100 Parentcommunity-reported, escalating at 150 and 200
- 110 Runnercommunity-reported
If you’re staying in, filter the room you’re actually in
Two mountain walls and the nights the wind quits
December and January are the months to watch here, not fire season. The Santa Clara Valley is walled by the Santa Cruz Mountains on the west and the Diablo Range on the east, and it narrows as it runs southeast, so its main ventilation is marine air drawn down the length of San Francisco Bay. On a cold, clear, windless night that flow stops, a warmer layer settles over the valley floor, and whatever is released stays near the ground until the next system moves through.
What fills that lid is mostly residential wood smoke. The Bay Area Air District calls wood burning the leading source of the region’s wintertime PM2.5, roughly a third of it, and makes burning illegal district-wide on a Winter Spare the Air day under Regulation 6, Rule 3, which runs November 1 through the end of February. For a metro of this size the pollutant deciding a bad winter day is not the freeway. It is fireplaces, and the enforcement follows.
The rest of the year runs on the opposite mechanism. Afternoon onshore flow through the Bay scours the valley daily, which is why summer readings tend to be unremarkable unless regional wildfire smoke is sitting overhead. The split is counterintuitive on the ground: the still, bright, cold mornings that look cleanest are the ones the monitors read worst.
Where this number sits
Of the 121 US metros reporting to us right now, San Jose is number 28 and number 5 of the 12 we track in California. The pollutant driving it today is PM2.5.
Nearby metros we also measure, and what they read at the same hour:
- Oakland, CA — 38 miles away, AQI 48
- Stockton, CA — 54 miles away, AQI 51
- Sacramento, CA — 88 miles away, AQI 38
- Fresno, CA — 123 miles away, AQI 70
Where this reading comes from
AirNow’s San Jose reporting area, about 0.9 miles from the metro centre.
What has air quality in San Jose actually been?
0 of the 30 days we have recorded so far went above AQI 100.
| Date | Daily max AQI | EPA band | Hours read |
|---|---|---|---|
| 59 | Moderate | 22 | |
| 53 | Moderate | 20 | |
| 70 | Moderate | 20 | |
| 67 | Moderate | 23 | |
| 100 | Moderate | 23 | |
| 97 | Moderate | 22 | |
| 61 | Moderate | 23 | |
| 53 | Moderate | 23 | |
| 42 | Good | 20 | |
| 54 | Moderate | 20 | |
| 52 | Moderate | 23 | |
| 58 | Moderate | 24 | |
| 53 | Moderate | 23 | |
| 58 | Moderate | 23 | |
| 60 | Moderate | 23 | |
| 60 | Moderate | 20 | |
| 59 | Moderate | 20 | |
| 61 | Moderate | 22 | |
| 67 | Moderate | 23 | |
| 57 | Moderate | 23 | |
| 58 | Moderate | 23 | |
| 60 | Moderate | 24 | |
| 55 | Moderate | 20 | |
| 55 | Moderate | 21 | |
| 48 | Good | 23 | |
| 69 | Moderate | 23 | |
| 85 | Moderate | 23 | |
| 63 | Moderate | 23 | |
| 63 | Moderate | 26 | |
| 52 | Moderate | 6 — partial day |
Questions about San Jose
What is the air quality in San Jose right now?
Which monitor does this number come from?
How does San Jose compare with metros nearby?
Does this include pollen?
Put this number in context
Updated