Seattle Air Quality in Summer
Across 2019–2025, Seattle's summer (June–August) air quality had a median AQI of 44 (Good) over 644 monitored days in the Seattle-Tacoma-Bellevue, WA area. 4.1% of summer days (26 of 644) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 52.5% of days. The cleanest summer on record here was 2019 (median AQI 41, 0 days above 100) and the worst was 2023 (median 47, 7 days above 100, peak AQI 195).
- Good: 67.4%
- Moderate: 28.6%
- Unhealthy for Sensitive Groups: 3.0%
- Unhealthy or worse: 1.1%
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How is the air in Seattle in summer?
Good on a typical day: median AQI 44 across 2019–2025, with 4.1% of summer days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓67.4% of summer days were Good (AQI 0–50), 28.6% Moderate (51–100).
- ✓26 days of 644 reached AQI 101+; the summer peak was 195.
- ✓Cleanest month: June; worst month: July.
Frequently asked questions
What is the air quality like in Seattle in summer?▾
Across 2019–2025, the median daily AQI in Seattle in summer was 44 (Good). 67.4% of days were Good, 28.6% Moderate, and 4.1% reached Unhealthy for Sensitive Groups or worse, based on 644 monitored days in EPA's Air Quality System.
Is summer a good time for outdoor exercise in Seattle?▾
A typical summer day in Seattle sits in the Good range (median AQI 44), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 24 of summer days (4.1%) reached AQI 101+ in 2019–2025.
Which pollutant causes Seattle's summer air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 52.5% of summer days in Seattle. The highest summer AQI recorded in 2019–2025 was 195 (Unhealthy), in 2023.
Seattle summer air quality, year by year
Seattle summer air quality by year (Seattle-Tacoma-Bellevue, WA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019cleanest | 92 | 41 | 0 | 87 | PM2.5 |
| 2020 | 92 | 42 | 3 | 155 | PM2.5 |
| 2021 | 92 | 46 | 5 | 177 | O3 |
| 2022 | 92 | 44 | 7 | 143 | O3 |
| 2023worst | 92 | 47 | 7 | 195 | O3 |
| 2024 | 92 | 46 | 4 | 166 | PM2.5 |
| 2025 | 92 | 44 | 0 | 90 | PM2.5 |
What summer air means in Seattle
A typical summer day in Seattle sits in the Good range (median AQI 44), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 24 of summer days (4.1%) reached AQI 101+ in 2019–2025.
Summer's median AQI of 44 is below Seattle's whole-year median of 49, making it one of the area's cleaner periods. Nationally, the median Summer AQI across every EPA metro area (308,645 metro-days, 2019–2025) is 46, so Seattle runs in line with the national Summer norm; 4.1% of its Summer days topped AQI 100 versus 3.6% nationally (about the same).
Within the season, June is the cleanest month (median AQI 42, 2.4% of days above 100) and July the worst (median 44, 6.0% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Seattle
The latest EPA AirNow observation puts Seattle's AQI at 37 (PM2.5). The figures above are multi-year season statistics, not today's reading.
View current Seattle air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Seattle-Tacoma-Bellevue, 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.