Harrisburg Air Quality in December
Across 2019–2025, Harrisburg's December air quality had a median AQI of 52 (Moderate) over 217 monitored days in the Harrisburg-Carlisle, PA area. 2.3% of December days (5 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 2025 (median AQI 51, 0 days above 100) and the worst was 2020 (median 54, 3 days above 100, peak AQI 137).
- Good: 44.2%
- Moderate: 53.5%
- Unhealthy for Sensitive Groups: 2.3%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Harrisburg
Today's main pollutant in Harrisburg is ground-level ozone (AQI 48). 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.
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How is the air in Harrisburg in December?
Moderate on a typical day: median AQI 52 across 2019–2025, with 2.3% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓44.2% of December days were Good (AQI 0–50), 53.5% Moderate (51–100).
- ✓5 days of 217 reached AQI 101+; the December peak was 137.
- ✓Best December: 2025; worst December: 2020.
Frequently asked questions
What is the air quality like in Harrisburg in December?▾
Across 2019–2025, the median daily AQI in Harrisburg in December was 52 (Moderate). 44.2% of days were Good, 53.5% Moderate, and 2.3% 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 Harrisburg?▾
A typical December day in Harrisburg is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 43 of December days (2.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Harrisburg's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 91.7% of December days in Harrisburg. The highest December AQI recorded in 2019–2025 was 137 (Unhealthy for Sensitive Groups), in 2020.
Harrisburg December air quality, year by year
Harrisburg December air quality by year (Harrisburg-Carlisle, PA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 52 | 1 | 106 | PM2.5 |
| 2020worst | 31 | 54 | 3 | 137 | PM2.5 |
| 2021 | 31 | 60 | 0 | 85 | PM2.5 |
| 2022 | 31 | 52 | 1 | 127 | PM2.5 |
| 2023 | 31 | 52 | 0 | 94 | PM2.5 |
| 2024 | 31 | 52 | 0 | 88 | PM2.5 |
| 2025cleanest | 31 | 51 | 0 | 78 | PM2.5 |
What December air means in Harrisburg
A typical December day in Harrisburg is Moderate (median AQI 52): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 43 of December days (2.3%) 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 52 is in line with Harrisburg's whole-year median of 50, 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 Harrisburg runs above the national December norm; 2.3% of its December days topped AQI 100 versus 0.7% nationally (above average).
December is part of Harrisburg's winter season (December, January, February); the winter page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Harrisburg
The latest EPA AirNow observation puts Harrisburg's AQI at 48 (O3). The figures above are multi-year month statistics, not today's reading.
View current Harrisburg air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Harrisburg-Carlisle, PA), 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.