Los Angeles Air Quality in September
Across 2019–2025, Los Angeles's September air quality had a median AQI of 101 (Unhealthy for Sensitive Groups) over 210 monitored days in the Los Angeles-Long Beach-Anaheim, CA area. 50.0% of September days (105 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 77.1% of days. The cleanest September on record here was 2025 (median AQI 66, 7 days above 100) and the worst was 2020 (median 161, 28 days above 100, peak AQI 235).
- Good: 6.7%
- Moderate: 43.3%
- Unhealthy for Sensitive Groups: 31.0%
- Unhealthy or worse: 19.0%
Reduce Indoor Ozone in Los Angeles
Today's main pollutant in Los Angeles is ground-level ozone (AQI 38). 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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How is the air in Los Angeles in September?
Unhealthy for Sensitive Groups on a typical day: median AQI 101 across 2019–2025, with 50.0% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓6.7% of September days were Good (AQI 0–50), 43.3% Moderate (51–100).
- ✓105 days of 210 reached AQI 101+; the September peak was 235.
- ✓Best September: 2025; worst September: 2020.
Frequently asked questions
What is the air quality like in Los Angeles in September?▾
Across 2019–2025, the median daily AQI in Los Angeles in September was 101 (Unhealthy for Sensitive Groups). 6.7% of days were Good, 43.3% Moderate, and 50.0% 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 Los Angeles?▾
A typical September day in Los Angeles is already Unhealthy for Sensitive Groups (median AQI 101): people with asthma or heart disease, children and older adults should reduce prolonged outdoor exertion on most days, and about 50% of September days (50.0%) were at that level or worse.
Which pollutant causes Los Angeles's September air quality problems?▾
Ground-level ozone set the daily AQI on 77.1% of September days in Los Angeles. The highest September AQI recorded in 2019–2025 was 235 (Very Unhealthy), in 2020.
Los Angeles September air quality, year by year
Los Angeles September air quality by year (Los Angeles-Long Beach-Anaheim, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 84 | 11 | 190 | O3 |
| 2020worst | 30 | 161 | 28 | 235 | O3 |
| 2021 | 30 | 103 | 16 | 161 | O3 |
| 2022 | 30 | 87 | 11 | 209 | O3 |
| 2023 | 30 | 90 | 9 | 164 | O3 |
| 2024 | 30 | 122 | 23 | 209 | O3 |
| 2025cleanest | 30 | 66 | 7 | 182 | O3 |
What September air means in Los Angeles
A typical September day in Los Angeles is already Unhealthy for Sensitive Groups (median AQI 101): people with asthma or heart disease, children and older adults should reduce prolonged outdoor exertion on most days, and about 50% of September days (50.0%) were at that level or worse.
September's median AQI of 101 is above Los Angeles's whole-year median of 74, making it one of the area's dirtier periods. Nationally, the median September AQI across every EPA metro area (100,699 metro-days, 2019–2025) is 43, so Los Angeles runs above the national September norm; 50.0% of its September days topped AQI 100 versus 2.7% nationally (above average).
September is part of Los Angeles's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Los Angeles
The latest EPA AirNow observation puts Los Angeles's AQI at 38 (O3). The figures above are multi-year month statistics, not today's reading.
View current Los Angeles air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Los Angeles-Long Beach-Anaheim, 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.