San Jose Air Quality in Fall
Across 2019–2025, San Jose's fall (September–November) air quality had a median AQI of 52 (Moderate) over 637 monitored days in the San Jose-Sunnyvale-Santa Clara, CA area. 2.9% of fall days (18 of 637) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 58.2% of days. The cleanest fall on record here was 2025 (median AQI 37, 0 days above 100) and the worst was 2020 (median 63, 12 days above 100, peak AQI 198).
- Good: 47.7%
- Moderate: 49.5%
- Unhealthy for Sensitive Groups: 1.6%
- Unhealthy or worse: 1.3%
Extra Protection for San Jose Homes
Air quality in San Jose is moderate (AQI 53), with fine particles (PM2.5) the main concern. A True-HEPA purifier gives sensitive groups — kids, seniors and anyone with asthma or allergies — cleaner air indoors on days like today.
Recommended: Coway AP-1512HH Mighty — True HEPA + carbon · CADR ~246 CFM · rooms up to 361 sq ft
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How is the air in San Jose in fall?
Moderate on a typical day: median AQI 52 across 2019–2025, with 2.9% of fall days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓47.7% of fall days were Good (AQI 0–50), 49.5% Moderate (51–100).
- ✓18 days of 637 reached AQI 101+; the fall peak was 198.
- ✓Cleanest month: November; worst month: September.
Frequently asked questions
What is the air quality like in San Jose in fall?▾
Across 2019–2025, the median daily AQI in San Jose in fall was 52 (Moderate). 47.7% of days were Good, 49.5% Moderate, and 2.9% reached Unhealthy for Sensitive Groups or worse, based on 637 monitored days in EPA's Air Quality System.
Is fall a good time for outdoor exercise in San Jose?▾
A typical fall day in San Jose is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 34 of fall days (2.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes San Jose's fall air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 58.2% of fall days in San Jose. The highest fall AQI recorded in 2019–2025 was 198 (Unhealthy), in 2020.
San Jose fall air quality, year by year
San Jose fall air quality by year (San Jose-Sunnyvale-Santa Clara, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 91 | 52 | 0 | 98 | PM2.5 |
| 2020worst | 91 | 63 | 12 | 198 | PM2.5 |
| 2021 | 91 | 55 | 4 | 129 | PM2.5 |
| 2022 | 91 | 55 | 1 | 119 | PM2.5 |
| 2023 | 91 | 49 | 1 | 134 | PM2.5 |
| 2024 | 91 | 50 | 0 | 78 | PM2.5 |
| 2025cleanest | 91 | 37 | 0 | 71 | O3 |
What fall air means in San Jose
A typical fall day in San Jose is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 34 of fall days (2.9%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Fall's median AQI of 52 is in line with San Jose's whole-year median of 50, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median Fall AQI across every EPA metro area (296,275 metro-days, 2019–2025) is 40, so San Jose runs above the national Fall norm; 2.9% of its Fall days topped AQI 100 versus 1.5% nationally (above average).
Within the season, November is the cleanest month (median AQI 52, 0.0% of days above 100) and September the worst (median 50, 6.2% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in San Jose
The latest EPA AirNow observation puts San Jose's AQI at 53 (PM2.5). The figures above are multi-year season statistics, not today's reading.
View current San Jose air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (San Jose-Sunnyvale-Santa Clara, CA), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.