San Jose Air Quality in January
Across 2019–2025, San Jose's January air quality had a median AQI of 47 (Good) over 217 monitored days in the San Jose-Sunnyvale-Santa Clara, CA area. 0.0% of January days (0 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 68.2% of days. The cleanest January on record here was 2025 (median AQI 36, 0 days above 100) and the worst was 2022 (median 65, 0 days above 100, peak AQI 87).
- Good: 54.8%
- Moderate: 45.2%
- Unhealthy for Sensitive Groups: 0.0%
- 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.
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How is the air in San Jose in January?
Good on a typical day: median AQI 47 across 2019–2025, with 0.0% of January days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓54.8% of January days were Good (AQI 0–50), 45.2% Moderate (51–100).
- ✓0 days of 217 reached AQI 101+; the January peak was 87.
- ✓Best January: 2025; worst January: 2022.
Frequently asked questions
What is the air quality like in San Jose in January?▾
Across 2019–2025, the median daily AQI in San Jose in January was 47 (Good). 54.8% of days were Good, 45.2% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is January a good time for outdoor exercise in San Jose?▾
A typical January 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 January days reached AQI 101+ in 2019–2025.
Which pollutant causes San Jose's January air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 68.2% of January days in San Jose. The highest January AQI recorded in 2019–2025 was 87 (Moderate), in 2022.
San Jose January air quality, year by year
San Jose January 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 | 50 | 0 | 71 | PM2.5 |
| 2020 | 31 | 52 | 0 | 69 | PM2.5 |
| 2021 | 31 | 61 | 0 | 84 | PM2.5 |
| 2022worst | 31 | 65 | 0 | 87 | PM2.5 |
| 2023 | 31 | 39 | 0 | 83 | O3 |
| 2024 | 31 | 42 | 0 | 80 | PM2.5 |
| 2025cleanest | 31 | 36 | 0 | 62 | O3 |
What January air means in San Jose
A typical January 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 January days reached AQI 101+ in 2019–2025.
January'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 January AQI across every EPA metro area (95,602 metro-days, 2019–2025) is 39, so San Jose runs above the national January norm; 0.0% of its January days topped AQI 100 versus 0.7% nationally (about the same).
January 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.