San Jose Air Quality in October
Across 2019–2025, San Jose's October air quality had a median AQI of 52 (Moderate) over 217 monitored days in the San Jose-Sunnyvale-Santa Clara, CA area. 2.3% of October days (5 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 51.2% of days. The cleanest October on record here was 2025 (median AQI 37, 0 days above 100) and the worst was 2020 (median 63, 3 days above 100, peak AQI 168).
- Good: 47.5%
- Moderate: 50.2%
- Unhealthy for Sensitive Groups: 0.9%
- Unhealthy or worse: 1.4%
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 October?
Moderate on a typical day: median AQI 52 across 2019–2025, with 2.3% of October days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓47.5% of October days were Good (AQI 0–50), 50.2% Moderate (51–100).
- ✓5 days of 217 reached AQI 101+; the October peak was 168.
- ✓Best October: 2025; worst October: 2020.
Frequently asked questions
What is the air quality like in San Jose in October?▾
Across 2019–2025, the median daily AQI in San Jose in October was 52 (Moderate). 47.5% of days were Good, 50.2% Moderate, and 2.3% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in San Jose?▾
A typical October 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 43 of October days (2.3%) 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 October air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 51.2% of October days in San Jose. The highest October AQI recorded in 2019–2025 was 168 (Unhealthy), in 2020.
San Jose October air quality, year by year
San Jose October 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 | 31 | 53 | 0 | 88 | PM2.5 |
| 2020worst | 31 | 63 | 3 | 168 | PM2.5 |
| 2021 | 31 | 48 | 2 | 129 | PM2.5 |
| 2022 | 31 | 55 | 0 | 70 | PM2.5 |
| 2023 | 31 | 46 | 0 | 90 | O3 |
| 2024 | 31 | 53 | 0 | 77 | PM2.5 |
| 2025cleanest | 31 | 37 | 0 | 71 | O3 |
What October air means in San Jose
A typical October 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 43 of October days (2.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
October'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 October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so San Jose runs above the national October norm; 2.3% of its October days topped AQI 100 versus 1.3% nationally (about the same).
October is part of San Jose's fall season (September, October, November); the fall page pools all three months.
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 month 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.