San Diego Air Quality in September
Across 2019–2025, San Diego's September air quality had a median AQI of 70 (Moderate) over 210 monitored days in the San Diego-Carlsbad, CA area. 17.6% of September days (37 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 51.9% of days. The cleanest September on record here was 2025 (median AQI 55, 0 days above 100) and the worst was 2020 (median 102, 15 days above 100, peak AQI 192).
- Good: 11.4%
- Moderate: 71.0%
- Unhealthy for Sensitive Groups: 13.3%
- Unhealthy or worse: 4.3%
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 September?
Moderate on a typical day: median AQI 70 across 2019–2025, with 17.6% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓11.4% of September days were Good (AQI 0–50), 71.0% Moderate (51–100).
- ✓37 days of 210 reached AQI 101+; the September peak was 192.
- ✓Best September: 2025; worst September: 2020.
Frequently asked questions
What is the air quality like in San Diego in September?▾
Across 2019–2025, the median daily AQI in San Diego in September was 70 (Moderate). 11.4% of days were Good, 71.0% Moderate, and 17.6% reached Unhealthy for Sensitive Groups or worse, based on 210 monitored days in EPA's Air Quality System.
Is September a good time for outdoor exercise in San Diego?▾
A typical September day in San Diego is Moderate (median AQI 70): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 6 of September days (17.6%) 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 September air quality problems?▾
Ground-level ozone set the daily AQI on 51.9% of September days in San Diego. The highest September AQI recorded in 2019–2025 was 192 (Unhealthy), in 2020.
San Diego September air quality, year by year
San Diego September 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 | 30 | 66 | 1 | 147 | PM2.5 |
| 2020worst | 30 | 102 | 15 | 192 | PM2.5 |
| 2021 | 30 | 80 | 4 | 133 | O3 |
| 2022 | 30 | 66 | 5 | 145 | O3 |
| 2023 | 30 | 67 | 3 | 115 | PM2.5 |
| 2024 | 30 | 87 | 9 | 161 | O3 |
| 2025cleanest | 30 | 55 | 0 | 87 | PM2.5 |
What September air means in San Diego
A typical September day in San Diego is Moderate (median AQI 70): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 6 of September days (17.6%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
September's median AQI of 70 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 September AQI across every EPA metro area (100,699 metro-days, 2019–2025) is 43, so San Diego runs above the national September norm; 17.6% of its September days topped AQI 100 versus 2.7% nationally (above average).
September is part of San Diego's fall season (September, October, November); the fall page pools all three months.
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 month 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.