Portland, ME Air Quality in January
Across 2019–2025, Portland's January air quality had a median AQI of 40 (Good) over 217 monitored days in the Portland-South Portland, ME area. 0.0% of January days (0 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 52.5% of days. The cleanest January on record here was 2021 (median AQI 35, 0 days above 100) and the worst was 2019 (median 52, 0 days above 100, peak AQI 69).
- Good: 69.6%
- Moderate: 30.4%
- Unhealthy for Sensitive Groups: 0.0%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Portland
Today's main pollutant in Portland is ground-level ozone (AQI 29). 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 Portland in January?
Good on a typical day: median AQI 40 across 2019–2025, with 0.0% of January days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓69.6% of January days were Good (AQI 0–50), 30.4% Moderate (51–100).
- ✓0 days of 217 reached AQI 101+; the January peak was 79.
- ✓Best January: 2021; worst January: 2019.
Frequently asked questions
What is the air quality like in Portland in January?▾
Across 2019–2025, the median daily AQI in Portland in January was 40 (Good). 69.6% of days were Good, 30.4% Moderate, and 0.0% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is January a good time for outdoor exercise in Portland?▾
A typical January day in Portland sits in the Good range (median AQI 40), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of January days reached AQI 101+ in 2019–2025.
Which pollutant causes Portland's January air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 52.5% of January days in Portland. The highest January AQI recorded in 2019–2025 was 79 (Moderate), in 2019.
Portland January air quality, year by year
Portland January air quality by year (Portland-South Portland, ME, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019worst | 31 | 52 | 0 | 69 | PM2.5 |
| 2020 | 31 | 48 | 0 | 73 | PM2.5 |
| 2021cleanest | 31 | 35 | 0 | 65 | O3 |
| 2022 | 31 | 41 | 0 | 62 | PM2.5 |
| 2023 | 31 | 35 | 0 | 51 | O3 |
| 2024 | 31 | 38 | 0 | 79 | O3 |
| 2025 | 31 | 41 | 0 | 78 | O3 |
What January air means in Portland
A typical January day in Portland sits in the Good range (median AQI 40), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of January days reached AQI 101+ in 2019–2025.
January's median AQI of 40 is in line with Portland's whole-year median of 40, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median January AQI across every EPA metro area (95,602 metro-days, 2019–2025) is 39, so Portland runs in line with the national January norm; 0.0% of its January days topped AQI 100 versus 0.7% nationally (about the same).
January is part of Portland's winter season (December, January, February); the winter page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Portland
The latest EPA AirNow observation puts Portland's AQI at 29 (O3). The figures above are multi-year month statistics, not today's reading.
View current Portland air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Portland-South Portland, ME), 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.