Riverside Air Quality in September
Across 2019–2025, Riverside's September air quality had a median AQI of 122 (Unhealthy for Sensitive Groups) over 210 monitored days in the Riverside-San Bernardino-Ontario, CA area. 61.4% of September days (129 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 80.5% of days. The cleanest September on record here was 2025 (median AQI 87, 8 days above 100) and the worst was 2020 (median 163, 27 days above 100, peak AQI 230).
- Good: 1.4%
- Moderate: 37.1%
- Unhealthy for Sensitive Groups: 29.5%
- Unhealthy or worse: 31.9%
Extra Protection for Riverside Homes
Air quality in Riverside is moderate (AQI 58), 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 Riverside in September?
Unhealthy for Sensitive Groups on a typical day: median AQI 122 across 2019–2025, with 61.4% of September days above AQI 100. Ground-level ozone is the main driver.
- ✓1.4% of September days were Good (AQI 0–50), 37.1% Moderate (51–100).
- ✓129 days of 210 reached AQI 101+; the September peak was 593.
- ✓Best September: 2025; worst September: 2020.
Frequently asked questions
What is the air quality like in Riverside in September?▾
Across 2019–2025, the median daily AQI in Riverside in September was 122 (Unhealthy for Sensitive Groups). 1.4% of days were Good, 37.1% Moderate, and 61.4% 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 Riverside?▾
A typical September day in Riverside is already Unhealthy for Sensitive Groups (median AQI 122): people with asthma or heart disease, children and older adults should reduce prolonged outdoor exertion on most days, and about 61% of September days (61.4%) were at that level or worse.
Which pollutant causes Riverside's September air quality problems?▾
Ground-level ozone set the daily AQI on 80.5% of September days in Riverside. The highest September AQI recorded in 2019–2025 was 593 (Hazardous), in 2020.
Riverside September air quality, year by year
Riverside September air quality by year (Riverside-San Bernardino-Ontario, CA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 114 | 18 | 195 | O3 |
| 2020worst | 30 | 163 | 27 | 230 | O3 |
| 2021 | 30 | 124 | 19 | 202 | O3 |
| 2022 | 30 | 97 | 12 | 205 | O3 |
| 2023 | 30 | 112 | 20 | 228 | O3 |
| 2024 | 30 | 162 | 25 | 593 | O3 |
| 2025cleanest | 30 | 87 | 8 | 166 | O3 |
What September air means in Riverside
A typical September day in Riverside is already Unhealthy for Sensitive Groups (median AQI 122): people with asthma or heart disease, children and older adults should reduce prolonged outdoor exertion on most days, and about 61% of September days (61.4%) were at that level or worse.
September's median AQI of 122 is above Riverside's whole-year median of 89, 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 Riverside runs above the national September norm; 61.4% of its September days topped AQI 100 versus 2.7% nationally (above average).
September is part of Riverside's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Riverside
The latest EPA AirNow observation puts Riverside's AQI at 58 (PM2.5). The figures above are multi-year month statistics, not today's reading.
View current Riverside air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Riverside-San Bernardino-Ontario, 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.