San Diego Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for San Diego (San Diego-Carlsbad, CA area) was September 5, 2020, when the daily AQI reached 192 (Unhealthy), set by ground-level ozone. Across 2,557 monitored days in 2019–2025, 10 of the 10 worst days were Unhealthy (AQI 151+) or worse; 8 of the 10 were driven by fine particulate matter (PM2.5) and 2 by ground-level ozone, and 9 of them fell in 2020. The cleanest day was March 10, 2020 at AQI 28 (Good); the 10 best days span 4 different years.
Reduce Indoor Ozone in San Diego
Today's main pollutant in San Diego is ground-level ozone (AQI 34). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
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When were San Diego's worst and best air quality days?
Worst: September 5, 2020, AQI 192 (Unhealthy, O3). Best: March 10, 2020, AQI 28 (Good). Based on 2,557 EPA-monitored days in the San Diego-Carlsbad, CA area, 2019–2025.
- ✓10 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 165 (Unhealthy).
- ✓Fine particulate matter (PM2.5) drove 8 of the 10 worst days.
- ✓2020 accounts for 9 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in San Diego?▾
September 5, 2020: the San Diego-Carlsbad, CA area's daily AQI hit 192 (Unhealthy), driven by ground-level ozone. That is the highest of 2,557 monitored days in 2019–2025.
What was the best air quality day in San Diego?▾
March 10, 2020, with a daily AQI of 28 (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 San Diego's worst air quality day in 2025?▾
June 19, 2025, AQI 161 (Unhealthy), set by ground-level ozone, in peak ozone season.
Which pollutant causes San Diego's worst air days?▾
Fine particulate matter (PM2.5) set the AQI on 8 of the 10 worst days; ground-level ozone on 2. The tables above list the defining pollutant for every day.
San Diego's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the San Diego-Carlsbad, 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) | 192 | Unhealthy | O3 — ground-level ozone |
| 2 | (2020 page) | 180 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2020 page) | 177 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 4 | (2020 page) | 173 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 5 | (2019 page) | 169 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 6 | (2020 page) | 167 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 7 | (2020 page) | 167 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 8 | (2020 page) | 166 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 9 | (2020 page) | 166 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 10 | (2020 page) | 165 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
Worst day of each year in San Diego
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 | 169 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2020 | 192 | Unhealthy | O3 — ground-level ozone | |
| 2021 | 133 | Unhealthy for Sensitive Groups | O3 — ground-level ozone | |
| 2022 | 156 | Unhealthy | O3 — ground-level ozone | |
| 2023 | 150 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2024 | 161 | Unhealthy | O3 — ground-level ozone | |
| 2025 | 161 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
San Diego's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the San Diego-Carlsbad, CA area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2020 page) | 28 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 2 | (2023 page) | 30 | Good | O3 — ground-level ozone |
| 3 | (2020 page) | 31 | Good | O3 — ground-level ozone |
| 4 | (2019 page) | 33 | Good | O3 — ground-level ozone |
| 5 | (2024 page) | 35 | Good | O3 — ground-level ozone |
| 6 | (2023 page) | 35 | Good | O3 — ground-level ozone, in peak ozone season |
| 7 | (2023 page) | 35 | Good | O3 — ground-level ozone |
| 8 | (2020 page) | 35 | Good | O3 — ground-level ozone |
| 9 | (2019 page) | 35 | Good | O3 — ground-level ozone |
| 10 | (2024 page) | 36 | Good | O3 — ground-level ozone |
Right now in San Diego
The latest EPA AirNow observation puts San Diego's AQI at 34 (O3). The days above are historical records, 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.