San Jose Air Quality in Winter
Across 2019–2025, San Jose's winter (December–February) air quality had a median AQI of 47 (Good) over 632 monitored days in the San Jose-Sunnyvale-Santa Clara, CA area. 0.5% of winter days (3 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 64.9% of days. The cleanest winter on record here was 2025 (median AQI 35, 0 days above 100) and the worst was 2022 (median 60, 2 days above 100, peak AQI 103).
- Good: 54.4%
- Moderate: 45.1%
- Unhealthy for Sensitive Groups: 0.5%
- Unhealthy or worse: 0.0%
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 winter?
Good on a typical day: median AQI 47 across 2019–2025, with 0.5% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓54.4% of winter days were Good (AQI 0–50), 45.1% Moderate (51–100).
- ✓3 days of 632 reached AQI 101+; the winter peak was 105.
- ✓Cleanest month: February; worst month: December.
Frequently asked questions
What is the air quality like in San Jose in winter?▾
Across 2019–2025, the median daily AQI in San Jose in winter was 47 (Good). 54.4% of days were Good, 45.1% Moderate, and 0.5% reached Unhealthy for Sensitive Groups or worse, based on 632 monitored days in EPA's Air Quality System.
Is winter a good time for outdoor exercise in San Jose?▾
A typical winter day in San Jose sits in the Good range (median AQI 47), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Which pollutant causes San Jose's winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 64.9% of winter days in San Jose. The highest winter AQI recorded in 2019–2025 was 105 (Unhealthy for Sensitive Groups), in 2022.
San Jose winter air quality, year by year
San Jose winter 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 | 90 | 42 | 0 | 71 | PM2.5 |
| 2020 | 91 | 54 | 1 | 105 | PM2.5 |
| 2021 | 90 | 53 | 0 | 93 | PM2.5 |
| 2022worst | 90 | 60 | 2 | 103 | PM2.5 |
| 2023 | 90 | 46 | 0 | 88 | PM2.5 |
| 2024 | 91 | 46 | 0 | 100 | PM2.5 |
| 2025cleanest | 90 | 35 | 0 | 62 | O3 |
What winter air means in San Jose
A typical winter day in San Jose sits in the Good range (median AQI 47), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Winter's median AQI of 47 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 Winter AQI across every EPA metro area (278,620 metro-days, 2019–2025) is 40, so San Jose runs above the national Winter norm; 0.5% of its Winter days topped AQI 100 versus 0.6% nationally (about the same).
Within the season, February is the cleanest month (median AQI 42, 0.0% of days above 100) and December the worst (median 53, 1.4% 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.