Portland, OR Air Quality in Winter
Across 2019–2025, Portland's winter (December–February) air quality had a median AQI of 45 (Good) over 632 monitored days in the Portland-Vancouver-Hillsboro, OR-WA area. 0.5% of winter days (3 of 632) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 75.0% of days. The cleanest winter on record here was 2024 (median AQI 36, 0 days above 100) and the worst was 2019 (median 55, 2 days above 100, peak AQI 128).
- Good: 55.9%
- Moderate: 43.7%
- Unhealthy for Sensitive Groups: 0.5%
- Unhealthy or worse: 0.0%
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How is the air in Portland in winter?
Good on a typical day: median AQI 45 across 2019–2025, with 0.5% of winter days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓55.9% of winter days were Good (AQI 0–50), 43.7% Moderate (51–100).
- ✓3 days of 632 reached AQI 101+; the winter peak was 128.
- ✓Cleanest month: February; worst month: December.
Frequently asked questions
What is the air quality like in Portland in winter?▾
Across 2019–2025, the median daily AQI in Portland in winter was 45 (Good). 55.9% of days were Good, 43.7% Moderate, and 0.5% 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 Portland?▾
A typical winter day in Portland sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Which pollutant causes Portland's winter air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 75.0% of winter days in Portland. The highest winter AQI recorded in 2019–2025 was 128 (Unhealthy for Sensitive Groups), in 2019.
Portland winter air quality, year by year
Portland winter air quality by year (Portland-Vancouver-Hillsboro, OR-WA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019worst | 90 | 55 | 2 | 128 | PM2.5 |
| 2020 | 91 | 39 | 0 | 92 | PM2.5 |
| 2021 | 90 | 45 | 0 | 75 | PM2.5 |
| 2022 | 90 | 52 | 0 | 86 | PM2.5 |
| 2023 | 90 | 43 | 1 | 106 | PM2.5 |
| 2024cleanest | 91 | 36 | 0 | 77 | PM2.5 |
| 2025 | 90 | 45 | 0 | 88 | PM2.5 |
What winter air means in Portland
A typical winter day in Portland sits in the Good range (median AQI 45), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of winter days reached AQI 101+ in 2019–2025.
Winter's median AQI of 45 is above Portland's whole-year median of 41, making it one of the area's dirtier periods. Nationally, the median Winter AQI across every EPA metro area (278,620 metro-days, 2019–2025) is 40, so Portland runs above the national Winter norm; 0.5% of its Winter days topped AQI 100 versus 0.6% nationally (about the same).
Within the season, February is the cleanest month (median AQI 41, 0.5% of days above 100) and December the worst (median 49, 0.5% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Portland
The latest EPA AirNow observation puts Portland's AQI at 29 (PM2.5). The figures above are multi-year season 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-Vancouver-Hillsboro, OR-WA), 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.