Portland, OR Air Quality in Fall
Across 2019–2025, Portland's fall (September–November) air quality had a median AQI of 50 (Good) over 637 monitored days in the Portland-Vancouver-Hillsboro, OR-WA area. 2.8% of fall days (18 of 637) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 76.6% of days. The cleanest fall on record here was 2021 (median AQI 42, 0 days above 100) and the worst was 2020 (median 55, 11 days above 100, peak AQI 874).
- Good: 50.4%
- Moderate: 46.8%
- Unhealthy for Sensitive Groups: 0.9%
- Unhealthy or worse: 1.9%
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How is the air in Portland in fall?
Good on a typical day: median AQI 50 across 2019–2025, with 2.8% of fall days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓50.4% of fall days were Good (AQI 0–50), 46.8% Moderate (51–100).
- ✓18 days of 637 reached AQI 101+; the fall peak was 874.
- ✓Cleanest month: November; worst month: September.
Frequently asked questions
What is the air quality like in Portland in fall?▾
Across 2019–2025, the median daily AQI in Portland in fall was 50 (Good). 50.4% of days were Good, 46.8% Moderate, and 2.8% reached Unhealthy for Sensitive Groups or worse, based on 637 monitored days in EPA's Air Quality System.
Is fall a good time for outdoor exercise in Portland?▾
A typical fall day in Portland sits in the Good range (median AQI 50), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 36 of fall days (2.8%) reached AQI 101+ in 2019–2025.
Which pollutant causes Portland's fall air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 76.6% of fall days in Portland. The highest fall AQI recorded in 2019–2025 was 874 (Hazardous), in 2020.
Portland fall air quality, year by year
Portland fall 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 |
|---|---|---|---|---|---|
| 2019 | 91 | 50 | 0 | 94 | PM2.5 |
| 2020worst | 91 | 55 | 11 | 874 | PM2.5 |
| 2021cleanest | 91 | 42 | 0 | 80 | PM2.5 |
| 2022 | 91 | 58 | 5 | 175 | PM2.5 |
| 2023 | 91 | 52 | 0 | 87 | PM2.5 |
| 2024 | 91 | 38 | 2 | 127 | PM2.5 |
| 2025 | 91 | 48 | 0 | 78 | PM2.5 |
What fall air means in Portland
A typical fall day in Portland sits in the Good range (median AQI 50), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 36 of fall days (2.8%) reached AQI 101+ in 2019–2025.
Fall's median AQI of 50 is above Portland's whole-year median of 41, making it one of the area's dirtier periods. Nationally, the median Fall AQI across every EPA metro area (296,275 metro-days, 2019–2025) is 40, so Portland runs above the national Fall norm; 2.8% of its Fall days topped AQI 100 versus 1.5% nationally (above average).
Within the season, November is the cleanest month (median AQI 54, 1.0% of days above 100) and September the worst (median 40, 5.7% 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.