# San Jose, CA Air Quality Index (AQI) Today > Source: https://breathecheck.com/air-quality/us/california/san-jose/ > Live AQI for San Jose, CA with a plain verdict — go, short and unloaded, or don't go — plus the monitor behind it and our own hourly record. # San Jose, CA Air Quality Index (AQI) Today Readings collected automatically every hour; text written and checked by BreatheCheck Editorial . How this page is made → 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 runner one runner’s own 156-run log - 75–100 Daycare / school parents and staff in one r/toddlers thread, Aug 2025 — not a published rule - 100 Parent community-reported, escalating at 150 and 200 - 110 Runner community-reported EPA classifies 101–150 as Unhealthy for Sensitive Groups. That is an attributed classification, not a verdict on your lungs specifically. If you’re staying in, filter the room you’re actually in A portable HEPA unit or a Corsi-Rosenthal box — one builder put theirs at about $130 for a 12×14 bedroom. We don’t default to a MERV-13 swap in whole-house HVAC: it can restrict airflow, and the safe version needs a static-pressure check first. Dominant pollutant PM2.5 UV index 5 moderate · modelled UV hour by hour in San Jose → Days above AQI 100 0 of 30 days we have recorded The record, day by day → ### 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 Why a metro a short drive away reads differently → 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? Daily maximum, our own readings. 30 days since 2026-08-16; nothing back-filled. Why we keep our own → 0 of the 30 days we have recorded so far went above AQI 100. | Date | Daily max AQI | EPA band | Hours read | | 2026-09-14 | 59 | Moderate | 22 | | 2026-09-13 | 53 | Moderate | 20 | | 2026-09-12 | 70 | Moderate | 20 | | 2026-09-11 | 67 | Moderate | 23 | | 2026-09-10 | 100 | Moderate | 23 | | 2026-09-09 | 97 | Moderate | 22 | | 2026-09-08 | 61 | Moderate | 23 | | 2026-09-07 | 53 | Moderate | 23 | | 2026-09-06 | 42 | Good | 20 | | 2026-09-05 | 54 | Moderate | 20 | | 2026-09-04 | 52 | Moderate | 23 | | 2026-09-03 | 58 | Moderate | 24 | | 2026-09-02 | 53 | Moderate | 23 | | 2026-09-01 | 58 | Moderate | 23 | | 2026-08-31 | 60 | Moderate | 23 | | 2026-08-30 | 60 | Moderate | 20 | | 2026-08-29 | 59 | Moderate | 20 | | 2026-08-28 | 61 | Moderate | 22 | | 2026-08-27 | 67 | Moderate | 23 | | 2026-08-26 | 57 | Moderate | 23 | | 2026-08-25 | 58 | Moderate | 23 | | 2026-08-24 | 60 | Moderate | 24 | | 2026-08-23 | 55 | Moderate | 20 | | 2026-08-22 | 55 | Moderate | 21 | | 2026-08-21 | 48 | Good | 23 | | 2026-08-20 | 69 | Moderate | 23 | | 2026-08-19 | 85 | Moderate | 23 | | 2026-08-18 | 63 | Moderate | 23 | | 2026-08-17 | 63 | Moderate | 26 | | 2026-08-16 | 52 | Moderate | 6 — partial day | ## Questions about San Jose **What is the air quality in San Jose right now?** AQI 51 — Moderate. That is number 28 of the 121 US metros reporting to us at this hour. **Which monitor does this number come from?** San Jose, about 0.9 miles from the metro centre. One instrument reports for the whole metro, so the side farthest from it is the least well described. **How does San Jose compare with metros nearby?** At this hour: Oakland 48, Stockton 51, Sacramento 38, Fresno 70. Readings that close together suggest one airshed rather than local sources. **Does this include pollen?** No. The AQI covers PM2.5 , PM10 , ozone, NO₂, SO₂ and CO. A high-pollen day can read clean here and still put someone in bed. What the number means, band by band → · UV in San Jose → · Why apps disagree → ## Put this number in context On this page Alert me when San Jose turns One email when it crosses your threshold. Updated 14 Sep 2026, 22:12 UTC