San Diego Air Quality in Winter
Across 2019–2025, San Diego's winter (December–February) air quality had a median AQI of 65 (Moderate) over 632 monitored days in the San Diego-Carlsbad, CA area. 2.7% of winter days (17 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 83.5% of days. The cleanest winter on record here was 2022 (median AQI 58, 0 days above 100) and the worst was 2025 (median 72, 8 days above 100, peak AQI 154).
- Good: 14.6%
- Moderate: 82.8%
- Unhealthy for Sensitive Groups: 2.5%
- Unhealthy or worse: 0.2%
Extra Protection for San Diego Homes
Air quality in San Diego is moderate (AQI 54), 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 Diego in winter?
Moderate on a typical day: median AQI 65 across 2019–2025, with 2.7% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓14.6% of winter days were Good (AQI 0–50), 82.8% Moderate (51–100).
- ✓17 days of 632 reached AQI 101+; the winter peak was 154.
- ✓Cleanest month: February; worst month: December.
Frequently asked questions
What is the air quality like in San Diego in winter?▾
Across 2019–2025, the median daily AQI in San Diego in winter was 65 (Moderate). 14.6% of days were Good, 82.8% Moderate, and 2.7% 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 Diego?▾
A typical winter day in San Diego is Moderate (median AQI 65): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 37 of winter days (2.7%) 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 Diego's winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 83.5% of winter days in San Diego. The highest winter AQI recorded in 2019–2025 was 154 (Unhealthy), in 2025.
San Diego winter air quality, year by year
San Diego winter air quality by year (San Diego-Carlsbad, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 90 | 58 | 1 | 101 | PM2.5 |
| 2020 | 91 | 72 | 1 | 101 | PM2.5 |
| 2021 | 90 | 69 | 0 | 93 | PM2.5 |
| 2022cleanest | 90 | 58 | 0 | 91 | PM2.5 |
| 2023 | 90 | 63 | 1 | 111 | PM2.5 |
| 2024 | 91 | 65 | 6 | 125 | PM2.5 |
| 2025worst | 90 | 72 | 8 | 154 | PM2.5 |
What winter air means in San Diego
A typical winter day in San Diego is Moderate (median AQI 65): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 37 of winter days (2.7%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Winter's median AQI of 65 is in line with San Diego's whole-year median of 67, 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 Diego runs above the national Winter norm; 2.7% of its Winter days topped AQI 100 versus 0.6% nationally (above average).
Within the season, February is the cleanest month (median AQI 59, 0.0% of days above 100) and December the worst (median 73, 5.5% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in San Diego
The latest EPA AirNow observation puts San Diego's AQI at 54 (PM2.5). The figures above are multi-year season statistics, not today's reading.
View current San Diego air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (San Diego-Carlsbad, 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.