Seattle Air Quality in October
Across 2019–2025, Seattle's October air quality had a median AQI of 53 (Moderate) over 217 monitored days in the Seattle-Tacoma-Bellevue, WA area. 6.0% of October days (13 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 86.2% of days. The cleanest October on record here was 2021 (median AQI 46, 0 days above 100) and the worst was 2022 (median 85, 13 days above 100, peak AQI 362).
- Good: 42.9%
- Moderate: 51.2%
- Unhealthy for Sensitive Groups: 2.3%
- Unhealthy or worse: 3.7%
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How is the air in Seattle in October?
Moderate on a typical day: median AQI 53 across 2019–2025, with 6.0% of October days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓42.9% of October days were Good (AQI 0–50), 51.2% Moderate (51–100).
- ✓13 days of 217 reached AQI 101+; the October peak was 362.
- ✓Best October: 2021; worst October: 2022.
Frequently asked questions
What is the air quality like in Seattle in October?▾
Across 2019–2025, the median daily AQI in Seattle in October was 53 (Moderate). 42.9% of days were Good, 51.2% Moderate, and 6.0% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in Seattle?▾
A typical October day in Seattle is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 17 of October days (6.0%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Seattle's October air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 86.2% of October days in Seattle. The highest October AQI recorded in 2019–2025 was 362 (Hazardous), in 2022.
Seattle October air quality, year by year
Seattle October air quality by year (Seattle-Tacoma-Bellevue, WA, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 56 | 0 | 86 | PM2.5 |
| 2020 | 31 | 53 | 0 | 81 | PM2.5 |
| 2021cleanest | 31 | 46 | 0 | 88 | PM2.5 |
| 2022worst | 31 | 85 | 13 | 362 | PM2.5 |
| 2023 | 31 | 52 | 0 | 87 | PM2.5 |
| 2024 | 31 | 49 | 0 | 96 | PM2.5 |
| 2025 | 31 | 51 | 0 | 61 | PM2.5 |
What October air means in Seattle
A typical October day in Seattle is Moderate (median AQI 53): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 17 of October days (6.0%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
October's median AQI of 53 is above Seattle's whole-year median of 49, making it one of the area's dirtier periods. Nationally, the median October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so Seattle runs above the national October norm; 6.0% of its October days topped AQI 100 versus 1.3% nationally (above average).
October is part of Seattle's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Seattle
The latest EPA AirNow observation puts Seattle's AQI at 42 (PM2.5). The figures above are multi-year month 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.