Portland, OR Air Quality in May
Across 2019–2025, Portland's May air quality had a median AQI of 39 (Good) over 217 monitored days in the Portland-Vancouver-Hillsboro, OR-WA area. 0.5% of May days (1 of 217) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 80.2% of days. The cleanest May on record here was 2022 (median AQI 36, 0 days above 100) and the worst was 2020 (median 38, 1 day above 100, peak AQI 112).
- Good: 88.9%
- Moderate: 10.6%
- Unhealthy for Sensitive Groups: 0.5%
- Unhealthy or worse: 0.0%
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How is the air in Portland in May?
Good on a typical day: median AQI 39 across 2019–2025, with 0.5% of May days above AQI 100. Ground-level ozone is the main driver.
- ✓88.9% of May days were Good (AQI 0–50), 10.6% Moderate (51–100).
- ✓1 day of 217 reached AQI 101+; the May peak was 112.
- ✓Best May: 2022; worst May: 2020.
Frequently asked questions
What is the air quality like in Portland in May?▾
Across 2019–2025, the median daily AQI in Portland in May was 39 (Good). 88.9% of days were Good, 10.6% Moderate, and 0.5% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is May a good time for outdoor exercise in Portland?▾
A typical May day in Portland sits in the Good range (median AQI 39), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of May days reached AQI 101+ in 2019–2025.
Which pollutant causes Portland's May air quality problems?▾
Ground-level ozone set the daily AQI on 80.2% of May days in Portland. The highest May AQI recorded in 2019–2025 was 112 (Unhealthy for Sensitive Groups), in 2020.
Portland May air quality, year by year
Portland May 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 | 31 | 39 | 0 | 84 | O3 |
| 2020worst | 31 | 38 | 1 | 112 | O3 |
| 2021 | 31 | 39 | 0 | 51 | O3 |
| 2022cleanest | 31 | 36 | 0 | 45 | O3 |
| 2023 | 31 | 46 | 0 | 67 | PM2.5 |
| 2024 | 31 | 39 | 0 | 61 | O3 |
| 2025 | 31 | 42 | 0 | 71 | O3 |
What May air means in Portland
A typical May day in Portland sits in the Good range (median AQI 39), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of May days reached AQI 101+ in 2019–2025.
May's median AQI of 39 is in line with Portland's whole-year median of 41, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median May AQI across every EPA metro area (104,064 metro-days, 2019–2025) is 44, so Portland runs below the national May norm; 0.5% of its May days topped AQI 100 versus 1.3% nationally (about the same).
May is part of Portland's spring season (March, April, May); the spring 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 (PM2.5). 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-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.