SmogRank / United States / Washington / Seattle
Seattle, month by month
Seattle has a measured daily mean on 1,370 days since 1 January 2023. Its worst month was August 2023, at 54 US AQI (10.9 µg/m³), 463rd of 1,980 cities on that month's world ranking. Its cleanest was May 2025, at 24 US AQI (4.4 µg/m³). 2025 averaged 34 US AQI (6.2 µg/m³), against 33 US AQI (6.0 µg/m³) in 2024.
Every month since 2023
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
Seattle's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| August 2023 | 5410.9 µg/m³ | 463rdof 1,980 | North-western United States and Canada, August 2023 |
| November 2023 | 529.6 µg/m³ | 717thof 2,243 | – |
| January 2025 | 529.6 µg/m³ | 1,064thof 2,474 | – |
| January 2026 | 478.4 µg/m³ | 1,389thof 2,617 | – |
| August 2026 | 448.0 µg/m³ | 1,619thof 2,896 | North-western United States and Canada, 4 to 22 August 2026 |
| October 2023 | 447.9 µg/m³ | 793rdof 2,012 | – |
Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.
Seattle's worst days
| Day | US AQI | Episode |
|---|---|---|
| 20 Aug 2023 | 12645.7 µg/m³ | North-western United States and Canada, August 2023 |
| 26 Aug 2023 | 9734.0 µg/m³ | North-western United States and Canada, August 2023 |
| 5 Jul 2023 | 9231.0 µg/m³ | Washington, United States, July 2023 |
| 6 Aug 2026 | 8527.5 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 27 Aug 2023 | 8426.8 µg/m³ | North-western United States and Canada, August 2023 |
| 5 Aug 2026 | 8226.0 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 21 Aug 2023 | 7823.7 µg/m³ | North-western United States and Canada, August 2023 |
| 28 Nov 2023 | 7823.7 µg/m³ | – |
| 4 Aug 2026 | 7522.1 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 25 Jan 2026 | 7421.4 µg/m³ | – |
Daily means, the highest since 1 Jan 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.
Use this history
SmogRank, PM2.5 monthly and daily means, Seattle, United States, 1 Jan 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/seattle/history (accessed 12 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.
Seattle now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 18:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).