Philadelphia Air Quality in Winter
Across 2019–2025, Philadelphia's winter (December–February) air quality had a median AQI of 57 (Moderate) over 632 monitored days in the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD area. 1.8% of winter days (11 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 91.5% of days. The cleanest winter on record here was 2024 (median AQI 54, 0 days above 100) and the worst was 2019 (median 60, 5 days above 100, peak AQI 133).
- Good: 23.4%
- Moderate: 74.8%
- Unhealthy for Sensitive Groups: 1.6%
- Unhealthy or worse: 0.2%
Reduce Indoor Ozone in Philadelphia
Today's main pollutant in Philadelphia is ground-level ozone (AQI 26). 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 Philadelphia in winter?
Moderate on a typical day: median AQI 57 across 2019–2025, with 1.8% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓23.4% of winter days were Good (AQI 0–50), 74.8% Moderate (51–100).
- ✓11 days of 632 reached AQI 101+; the winter peak was 168.
- ✓Cleanest month: February; worst month: December.
Frequently asked questions
What is the air quality like in Philadelphia in winter?▾
Across 2019–2025, the median daily AQI in Philadelphia in winter was 57 (Moderate). 23.4% of days were Good, 74.8% Moderate, and 1.8% reached Unhealthy for Sensitive Groups or worse, based on 632 monitored days in EPA's Air Quality System.
Is winter a good time for outdoor exercise in Philadelphia?▾
A typical winter day in Philadelphia is Moderate (median AQI 57): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 56 of winter days (1.8%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Philadelphia's winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 91.5% of winter days in Philadelphia. The highest winter AQI recorded in 2019–2025 was 168 (Unhealthy), in 2019.
Philadelphia winter air quality, year by year
Philadelphia winter air quality by year (Philadelphia-Camden-Wilmington, PA-NJ-DE-MD, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019worst | 90 | 60 | 5 | 133 | PM2.5 |
| 2020 | 91 | 57 | 1 | 103 | PM2.5 |
| 2021 | 90 | 58 | 0 | 99 | PM2.5 |
| 2022 | 90 | 58 | 1 | 113 | PM2.5 |
| 2023 | 90 | 59 | 3 | 108 | PM2.5 |
| 2024cleanest | 91 | 54 | 0 | 100 | PM2.5 |
| 2025 | 90 | 55 | 1 | 168 | PM2.5 |
What winter air means in Philadelphia
A typical winter day in Philadelphia is Moderate (median AQI 57): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 56 of winter days (1.8%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Winter's median AQI of 57 is in line with Philadelphia's whole-year median of 56, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median Winter AQI across every EPA metro area (278,620 metro-days, 2019–2025) is 40, so Philadelphia runs above the national Winter norm; 1.8% of its Winter days topped AQI 100 versus 0.6% nationally (above average).
Within the season, February is the cleanest month (median AQI 57, 1.0% of days above 100) and December the worst (median 57, 2.8% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Philadelphia
The latest EPA AirNow observation puts Philadelphia's AQI at 26 (O3). The figures above are multi-year season statistics, not today's reading.
View current Philadelphia air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Philadelphia-Camden-Wilmington, PA-NJ-DE-MD), 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.