Riverside Air Quality in December
Across 2019–2025, Riverside's December air quality had a median AQI of 68 (Moderate) over 217 monitored days in the Riverside-San Bernardino-Ontario, CA area. 12.4% of December days (27 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 91.7% of days. The cleanest December on record here was 2022 (median AQI 66, 0 days above 100) and the worst was 2024 (median 82, 9 days above 100, peak AQI 157).
- Good: 4.6%
- Moderate: 82.9%
- Unhealthy for Sensitive Groups: 8.3%
- Unhealthy or worse: 4.1%
Extra Protection for Riverside Homes
Air quality in Riverside is moderate (AQI 56), 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 December?
Moderate on a typical day: median AQI 68 across 2019–2025, with 12.4% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓4.6% of December days were Good (AQI 0–50), 82.9% Moderate (51–100).
- ✓27 days of 217 reached AQI 101+; the December peak was 187.
- ✓Best December: 2022; worst December: 2024.
Frequently asked questions
What is the air quality like in Riverside in December?▾
Across 2019–2025, the median daily AQI in Riverside in December was 68 (Moderate). 4.6% of days were Good, 82.9% Moderate, and 12.4% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is December a good time for outdoor exercise in Riverside?▾
A typical December day in Riverside is Moderate (median AQI 68): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 8 of December days (12.4%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Riverside's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 91.7% of December days in Riverside. The highest December AQI recorded in 2019–2025 was 187 (Unhealthy), in 2024.
Riverside December air quality, year by year
Riverside December 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 | 31 | 62 | 1 | 107 | PM2.5 |
| 2020 | 31 | 66 | 2 | 154 | PM2.5 |
| 2021 | 31 | 80 | 7 | 187 | PM2.5 |
| 2022cleanest | 31 | 66 | 0 | 92 | PM2.5 |
| 2023 | 31 | 67 | 3 | 146 | PM2.5 |
| 2024worst | 31 | 82 | 9 | 157 | PM2.5 |
| 2025 | 31 | 73 | 5 | 162 | PM2.5 |
What December air means in Riverside
A typical December day in Riverside is Moderate (median AQI 68): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 8 of December days (12.4%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
December's median AQI of 68 is below Riverside's whole-year median of 89, making it one of the area's cleaner periods. Nationally, the median December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so Riverside runs above the national December norm; 12.4% of its December days topped AQI 100 versus 0.7% nationally (above average).
December is part of Riverside's winter season (December, January, February); the winter 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 56 (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.