San Jose Air Quality in December
Across 2019–2025, San Jose's December air quality had a median AQI of 53 (Moderate) over 217 monitored days in the San Jose-Sunnyvale-Santa Clara, CA area. 1.4% of December days (3 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 71.4% of days. The cleanest December on record here was 2025 (median AQI 28, 0 days above 100) and the worst was 2022 (median 53, 2 days above 100, peak AQI 103).
- Good: 46.1%
- Moderate: 52.5%
- Unhealthy for Sensitive Groups: 1.4%
- 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
As an Amazon Associate, we earn from qualifying purchases.
How is the air in San Jose in December?
Moderate on a typical day: median AQI 53 across 2019–2025, with 1.4% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓46.1% of December days were Good (AQI 0–50), 52.5% Moderate (51–100).
- ✓3 days of 217 reached AQI 101+; the December peak was 105.
- ✓Best December: 2025; worst December: 2022.
Frequently asked questions
What is the air quality like in San Jose in December?▾
Across 2019–2025, the median daily AQI in San Jose in December was 53 (Moderate). 46.1% of days were Good, 52.5% Moderate, and 1.4% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is December a good time for outdoor exercise in San Jose?▾
A typical December day in San Jose is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 71 of December days (1.4%) 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 December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 71.4% of December days in San Jose. The highest December AQI recorded in 2019–2025 was 105 (Unhealthy for Sensitive Groups), in 2022.
San Jose December air quality, year by year
San Jose December 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 | 48 | 0 | 62 | PM2.5 |
| 2020 | 31 | 60 | 1 | 105 | PM2.5 |
| 2021 | 31 | 49 | 0 | 93 | PM2.5 |
| 2022worst | 31 | 53 | 2 | 103 | PM2.5 |
| 2023 | 31 | 57 | 0 | 88 | PM2.5 |
| 2024 | 31 | 59 | 0 | 100 | PM2.5 |
| 2025cleanest | 31 | 28 | 0 | 49 | O3 |
What December air means in San Jose
A typical December day in San Jose is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 71 of December days (1.4%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
December's median AQI of 53 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 December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so San Jose runs above the national December norm; 1.4% of its December days topped AQI 100 versus 0.7% nationally (about the same).
December is part of San Jose's winter season (December, January, February); the winter 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.