Seattle, WA Air Quality & Smog

Dominant pollutants, when smog is worst, notable historical episodes, and local agency resources for Seattle, WA — plus how to check the current AQI. For real-time readings, the free Smog Report iOS app pulls live air quality from EPA AirNow.

Dominant pollutants

PM2.5 (wildfire smoke summer + winter wood smoke), low ozone year-round.

Seasonal pattern: when smog is worst

Seattle's air-quality calendar is two-peaked: late-summer wildfire smoke (Aug-Sep) and winter inversions trapping wood-stove smoke (Nov-Feb). Outside those windows, marine ventilation keeps the air quite clean. Wildfire smoke from Eastern Washington and Canadian fires can persist for weeks in bad years.

A recent or notable event

September 2020 — Seattle was completely smoked in for nearly 2 weeks from combined Washington / Oregon / California fires; AQI exceeded 300 multiple days.

Local agencies and resources

PSCAA covers King, Pierce, Snohomish, and Kitsap counties — the densest local monitor network in WA.

• Washington State Department of Ecology
• Puget Sound Clean Air Agency (PSCAA)

How to check air quality in Seattle

The EPA's AirNow.gov publishes the canonical reading from the nearest regulatory monitor. For glanceable iPhone access — including widgets, Live Activities, Siri voice queries, and Apple Watch — install Smog Report. It's free, requires no account, and pulls from the same AirNow API.

For Seattle-specific advisories and alerts that go beyond the federal AirNow feed, check the agency pages above directly.

Common questions about Seattle air quality

Why does Seattle have air-quality and smog problems?

Seattle's air-quality calendar is two-peaked: late-summer wildfire smoke (Aug-Sep) and winter inversions trapping wood-stove smoke (Nov-Feb). Outside those windows, marine ventilation keeps the air quite clean. Wildfire smoke from Eastern Washington and Canadian fires can persist for weeks in bad years.

What are the main air pollutants in Seattle?

Seattle's dominant pollutants are PM2.5 (wildfire smoke summer + winter wood smoke), low ozone year-round. The AQI on any given day is usually driven by whichever of these is highest.

Has Seattle had a major air-quality or smog event?

September 2020 — Seattle was completely smoked in for nearly 2 weeks from combined Washington / Oregon / California fires; AQI exceeded 300 multiple days.

How can I check Seattle's air quality right now?

The EPA's AirNow.gov publishes the official reading from the nearest regulatory monitor. For live AQI on your iPhone — with home-screen widgets, Lock Screen Live Activities, Siri, and Apple Watch — the free Smog Report app pulls from the same AirNow feed. No account is required.

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