Washington Air Quality in December
Across 2019–2025, Washington's December air quality had a median AQI of 51 (Moderate) over 217 monitored days in the Washington-Arlington-Alexandria, DC-VA-MD-WV area. 0.0% of December days (0 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 85.3% of days. The cleanest December on record here was 2025 (median AQI 44, 0 days above 100) and the worst was 2021 (median 56, 0 days above 100, peak AQI 68).
- Good: 48.8%
- Moderate: 51.2%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
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How is the air in Washington in December?
Moderate on a typical day: median AQI 51 across 2019–2025, with 0.0% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓48.8% of December days were Good (AQI 0–50), 51.2% Moderate (51–100).
- ✓0 days of 217 reached AQI 101+; the December peak was 94.
- ✓Best December: 2025; worst December: 2021.
Frequently asked questions
What is the air quality like in Washington in December?▾
Across 2019–2025, the median daily AQI in Washington in December was 51 (Moderate). 48.8% of days were Good, 51.2% Moderate, and 0.0% 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 Washington?▾
A typical December day in Washington is Moderate (median AQI 51): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of December days reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Washington's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 85.3% of December days in Washington. The highest December AQI recorded in 2019–2025 was 94 (Moderate), in 2021.
Washington December air quality, year by year
Washington December air quality by year (Washington-Arlington-Alexandria, DC-VA-MD-WV, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 47 | 0 | 94 | PM2.5 |
| 2020 | 31 | 46 | 0 | 83 | PM2.5 |
| 2021worst | 31 | 56 | 0 | 68 | PM2.5 |
| 2022 | 31 | 54 | 0 | 74 | PM2.5 |
| 2023 | 31 | 51 | 0 | 74 | PM2.5 |
| 2024 | 31 | 47 | 0 | 71 | PM2.5 |
| 2025cleanest | 31 | 44 | 0 | 69 | PM2.5 |
What December air means in Washington
A typical December day in Washington is Moderate (median AQI 51): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and fewer than 1% of December days 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 51 is in line with Washington's whole-year median of 52, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so Washington runs above the national December norm; 0.0% of its December days topped AQI 100 versus 0.7% nationally (about the same).
December is part of Washington's winter season (December, January, February); the winter page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Washington
The latest EPA AirNow observation puts Washington's AQI at 37 (PM2.5). The figures above are multi-year month statistics, not today's reading.
View current Washington air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Washington-Arlington-Alexandria, DC-VA-MD-WV), 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.