Santa Rosa Air Quality in September
Across 2019–2025, Santa Rosa's September air quality had a median AQI of 29 (Good) over 210 monitored days in the Santa Rosa, CA area. 3.4% of September days (7 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 38.1% of days. The cleanest September on record here was 2024 (median AQI 9, 0 days above 100) and the worst was 2020 (median 54, 5 days above 100, peak AQI 199).
- Good: 80.5%
- Moderate: 16.2%
- Unhealthy for Sensitive Groups: 1.0%
- Unhealthy or worse: 2.4%
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How is the air in Santa Rosa in September?
Good on a typical day: median AQI 29 across 2019–2025, with 3.4% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓80.5% of September days were Good (AQI 0–50), 16.2% Moderate (51–100).
- ✓7 days of 210 reached AQI 101+; the September peak was 199.
- ✓Best September: 2024; worst September: 2020.
Frequently asked questions
What is the air quality like in Santa Rosa in September?▾
Across 2019–2025, the median daily AQI in Santa Rosa in September was 29 (Good). 80.5% of days were Good, 16.2% Moderate, and 3.4% 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 Santa Rosa?▾
A typical September day in Santa Rosa sits in the Good range (median AQI 29), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 29 of September days (3.4%) reached AQI 101+ in 2019–2025.
Which pollutant causes Santa Rosa's September air quality problems?▾
Ground-level ozone set the daily AQI on 38.1% of September days in Santa Rosa. The highest September AQI recorded in 2019–2025 was 199 (Unhealthy), in 2020.
Santa Rosa September air quality, year by year
Santa Rosa September air quality by year (Santa Rosa, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 33 | 0 | 52 | O3 |
| 2020worst | 30 | 54 | 5 | 199 | PM2.5 |
| 2021 | 30 | 40 | 0 | 65 | PM2.5 |
| 2022 | 30 | 31 | 0 | 63 | O3 |
| 2023 | 30 | 28 | 2 | 117 | O3 |
| 2024cleanest | 30 | 9 | 0 | 25 | PM10 |
| 2025 | 30 | 9 | 0 | 22 | PM10 |
What September air means in Santa Rosa
A typical September day in Santa Rosa sits in the Good range (median AQI 29), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 29 of September days (3.4%) reached AQI 101+ in 2019–2025.
September's median AQI of 29 is below Santa Rosa's whole-year median of 36, making it one of the area's cleaner periods. Nationally, the median September AQI across every EPA metro area (100,699 metro-days, 2019–2025) is 43, so Santa Rosa runs below the national September norm; 3.4% of its September days topped AQI 100 versus 2.7% nationally (about the same).
September is part of Santa Rosa's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Santa Rosa
The latest EPA AirNow observation puts Santa Rosa's AQI at 36 (PM2.5). The figures above are multi-year month statistics, not today's reading.
View current Santa Rosa air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Santa Rosa, 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.