Santa Rosa Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Santa Rosa (Santa Rosa, CA area) was September 11, 2020, when the daily AQI reached 199 (Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season. Across 2,557 monitored days in 2019–2025, 6 of the 10 worst days were Unhealthy (AQI 151+) or worse; 10 of the 10 were driven by fine particulate matter (PM2.5), and 8 of them fell in 2020. The cleanest day was December 21, 2025 at AQI 0 (Good); the 10 best days span 2 different years.
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When were Santa Rosa's worst and best air quality days?
Worst: September 11, 2020, AQI 199 (Unhealthy, PM2.5). Best: December 21, 2025, AQI 0 (Good). Based on 2,557 EPA-monitored days in the Santa Rosa, CA area, 2019–2025.
- ✓6 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 97 (Moderate).
- ✓Fine particulate matter (PM2.5) drove 10 of the 10 worst days.
- ✓2020 accounts for 8 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in Santa Rosa?▾
September 11, 2020: the Santa Rosa, CA area's daily AQI hit 199 (Unhealthy), driven by fine particulate matter (PM2.5), in wildfire smoke season. That is the highest of 2,557 monitored days in 2019–2025.
What was the best air quality day in Santa Rosa?▾
December 21, 2025, with a daily AQI of 0 (Good). The daily AQI is the highest reading from any monitor in the area, so even the cleanest day reflects the area's worst monitor.
What was Santa Rosa's worst air quality day in 2025?▾
January 26, 2025, AQI 39 (Good), set by coarse dust (PM10).
Which pollutant causes Santa Rosa's worst air days?▾
Fine particulate matter (PM2.5) set the AQI on 10 of the 10 worst days. The tables above list the defining pollutant for every day.
Santa Rosa's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Santa Rosa, CA area (EPA AQS). The daily AQI is the highest reading from any monitor in the area that day.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2020 page) | 199 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 2 | (2020 page) | 199 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2020 page) | 171 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 4 | (2020 page) | 165 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 5 | (2020 page) | 165 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 6 | (2020 page) | 153 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 7 | (2020 page) | 128 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 8 | (2023 page) | 117 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 9 | (2023 page) | 104 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 10 | (2020 page) | 97 | Moderate | PM2.5 — fine particulate matter (PM2.5) |
Worst day of each year in Santa Rosa
The single highest-AQI day in each year on record. Click a year for its full month-by-month statistics.
| Year | Worst day | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 2019 | 87 | Moderate | O3 — ground-level ozone, in peak ozone season | |
| 2020 | 199 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2021 | 89 | Moderate | PM2.5 — fine particulate matter (PM2.5) | |
| 2022 | 82 | Moderate | PM2.5 — fine particulate matter (PM2.5) | |
| 2023 | 117 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2024 | 72 | Moderate | PM2.5 — fine particulate matter (PM2.5) | |
| 2025 | 39 | Good | PM10 — coarse dust (PM10) |
Santa Rosa's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Santa Rosa, CA area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2025 page) | 0 | Good | PM10 — coarse dust (PM10) |
| 2 | (2025 page) | 1 | Good | PM10 — coarse dust (PM10) |
| 3 | (2025 page) | 1 | Good | PM10 — coarse dust (PM10) |
| 4 | (2024 page) | 1 | Good | PM10 — coarse dust (PM10) |
| 5 | (2025 page) | 2 | Good | PM10 — coarse dust (PM10) |
| 6 | (2025 page) | 2 | Good | PM10 — coarse dust (PM10) |
| 7 | (2025 page) | 2 | Good | PM10 — coarse dust (PM10) |
| 8 | (2025 page) | 2 | Good | PM10 — coarse dust (PM10) |
| 9 | (2025 page) | 2 | Good | PM10 — coarse dust (PM10) |
| 10 | (2025 page) | 2 | Good | PM10 — coarse dust (PM10) |
Right now in Santa Rosa
The latest EPA AirNow observation puts Santa Rosa's AQI at 36 (PM2.5). The days above are historical records, 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.