Air Quality in Seattle, Washington — Live
Live readings from PurpleAir sensors across Seattle — with free alerts the moment smoke moves in.
AQI 37 from 4 PurpleAir sensors · Trending down · data from PurpleAir
As of , the air quality in Seattle, Washington is AQI 37 — Good and falling — with PM2.5 at 6.6 µg/m³, the median of 4 live PurpleAir sensors reading 29 to 43. Canairy's verdict: Breathe easy.
For scale, that PM2.5 reading is below the World Health Organization's 24-hour guideline of 15 µg/m³. The WHO figure is a daily average and this is a live reading, so read it as a sense of magnitude rather than a formal exceedance — a brief spike and a bad day are not the same thing. More on the WHO guidelines
Pollen today in Seattle: weeds pollen is the strongest of the three at a high level, from Google's pollen forecast. Canairy shows the tree, grass and weed forecast beside the air reading on every plan, including the free one.
Free to download · Live data from PurpleAir & public monitors
Live PurpleAir sensor map for Seattle and Bellevue, Renton, Shoreline, Kirkland. Every dot is a real sensor, color-coded by current air quality.
Sensor by sensor in Seattle
The sensors Canairy reads in Seattle agree right now — all 4 sit in the Good band, a 14-point spread — so the city-wide number is a fair description of the whole area today.
| From city center | AQI | Category |
|---|---|---|
| 1.5 mi NE | 37 | Good |
| 2.0 mi SE | 43 | Good |
| 3.3 mi SW | 37 | Good |
| 5.1 mi NW | 29 | Good |
For most of the year Seattle breathes some of the cleanest air of any big US city, scrubbed by marine wind off the Pacific and the region's steady rain. The hard exception is late-summer wildfire smoke: in September 2020 and again in October 2022, smoke settled over the Puget Sound basin thickly enough to give Seattle the worst air quality of any major city on Earth, ahead of Beijing and Delhi.
What Canairy does for Seattle
A clear verdict
Not just a number — a plain-English call for Seattle: open the windows, or keep them shut.
Smoke alerts
A push or text the moment the air crosses your threshold — and again when it clears.
A heads-up before it's bad
Trend alerts catch the air turning, so you can close up the house before the smoke settles in.
Every place you care about
Home, work, the kids' school — across Seattle or across the country, on one screen.
What the air in Seattle is doing next
| When | AQI | Expected air quality | Main pollutant |
|---|---|---|---|
| Today | 33 | Good | PM2.5 |
| Tomorrow | 33 | Good | PM2.5 |
| Monday | 33 | Good | PM2.5 |
| Tuesday | 33 | Good | PM2.5 |
| Wednesday | 33 | Good | PM2.5 |
For Fri-Mon (Sep 4-7) We'll have mostly GOOD to MODERATE air quality this weekend. Late this afternoon and early evening, we may have some smoke moving into the Cascades and sneaking through the passes. Some areas could reach MODERATE or UNHEALTHY FOR SENSITIVE GROUPS for a few hours. Overnight and into Saturday, winds should shift back to westerly and mix the smoke and push it back east. This pattern could repeat again Saturday evening and Sun. Monday should have good westerly winds and GOOD air quality.
Forecast from EPA AirNow for the Seattle-Bellevue-Kent Valley reporting area. Canairy watches the live sensors against it and tells you when the air actually crosses your threshold, rather than leaving you to check.
Most days the marine air keeps Seattle's air clean
Seattle sits between Puget Sound and the Cascade Range, and for most of the year that geography works in its favor. Onshore wind off the cool Pacific and the region's frequent rain flush pollutants out before they build up, so a typical day here lands well inside the Good range rather than the Moderate-to-Unhealthy readings common in hotter, drier cities.
The catch is that the same basin that stays clean on a breezy day can hold pollution in on a still one. In fall and winter, marine inversions settle a lid of cool air over the Sound and trap whatever is underneath it, which is why local PM2.5 tends to run higher in the cold months than in summer even with no fire anywhere near the city.
The smoke seasons: 2018, 2020, and 2022
Seattle's worst air now arrives with wildfire smoke in late summer and early fall. In 2018 the Puget Sound Clean Air Agency counted nine wildfire-smoke days across the region, all in August, and the Beacon Hill monitor recorded a 24-hour PM2.5 of 57.3 micrograms per cubic meter on August 14, the highest reading at that site at the time in EPA records going back to 1999. September 2020 surpassed it: the Puget Sound Clean Air Agency measured the highest fine particle levels it had recorded since monitoring began in 1999, with smoke blanketing western Washington from September 7 to 21 after a wind shift steered Oregon-fire smoke over the Cascades and let it settle to ground level.
The October 2022 episode showed how close the fires can be. Smoke from the Bolt Creek Fire near Skykomish, only about 50 miles east of downtown, parked over the Sound and pushed Seattle's air into the unhealthy-to-very-unhealthy range by the Puget Sound Clean Air Agency's reckoning, putting the city at the top of IQAir's world ranking of major cities for two straight days. When high pressure stalls over the region, there is no marine wind to move the smoke, and it simply lingers until the next weather system arrives.
Winter wood smoke and the Duwamish Valley
Not all of Seattle's pollution comes from distant fires. On cold, still winter nights, smoke from home wood stoves and fireplaces collects under the inversion and can push neighborhood air into unhealthy territory. That is why the Puget Sound Clean Air Agency calls cold-weather burn bans across King, Kitsap, Pierce, and Snohomish counties, restricting wood burning when particle levels start to climb.
The heaviest year-round burden falls on the Duwamish Valley. South Park and Georgetown sit against the Port of Seattle, major highways, and rail and truck traffic, and University of Washington research found residents there breathe more diesel exhaust than people in neighborhoods like Queen Anne. The valley carries roughly double the youth asthma hospitalization rate of the rest of King County, so the reading closest to home matters far more here than a citywide average.
Seattle air quality FAQ
What is the air quality in Seattle right now?
As of September 5, 2026 at 5:09 AM PDT, the air quality in Seattle, Washington is AQI 37 — Good — with PM2.5 at 6.6 µg/m³, the median of 4 live PurpleAir sensors. Open the windows. Great for outdoor activity.
When is Seattle's air quality usually worst?
Two seasons stand out. Late summer and early fall bring wildfire smoke, which drove Seattle's worst air on record in September 2020 and again during the October 2022 Bolt Creek Fire. Then in the cold months, still nights and marine inversions trap wood smoke and traffic emissions close to the ground, so winter particle levels tend to run higher than summer even without a fire.
Has Seattle really had the worst air quality in the world?
Yes, briefly. During the September 2020 smoke siege and again in October 2022, wildfire smoke settled over the Puget Sound basin thickly enough that Seattle topped global city rankings for air pollution, with the AQI passing 240 and beating out cities like Beijing and Delhi. Those are short-lived spikes tied to specific fires, not everyday conditions.
What the AQI numbers mean
| AQI | Category | What it means for you |
|---|---|---|
| 0–50 | Good | Open the windows. Great for outdoor activity. |
| 51–100 | Moderate | Sensitive groups may want to take it slower outside. |
| 101–150 | Unhealthy for Sensitive Groups | Kids, elderly, and respiratory conditions stay closer to home. |
| 151–200 | Unhealthy | Skip outdoor exercise. Close windows. |
| 201–300 | Very Unhealthy | Limit time outside. N95 if you must go. |
| 301+ | Hazardous | Health emergency. Stay inside, run filtration if you have it. |
Canairy lets you tighten these bands if you’re more sensitive than the EPA default, so an alert can fire before the official category changes. How to read the Air Quality Index
Where these readings come from
The AQI at the top of this page is the median of the 4 curated PurpleAir sensors Canairy tracks in and around Seattle, with outliers set aside so that one sensor brought indoors — or parked beside a barbecue — cannot set the number for a whole city. Every sensor behind it is listed above with its distance and bearing from the city center. There is no black box here.
In the app, a place you save resolves the same way first. When no neighborhood sensor is reporting it falls back to the nearest EPA AirNow monitor, and anything modeled rather than measured is labelled a regional estimate rather than passed off as a sensor reading. How low-cost sensors compare to regulatory monitors
About Canairy
Canairy is free to download. The free plan covers one saved place with live readings, a plain-English verdict, and push alerts when the air crosses a threshold you choose. Paid plans add more places, faster refreshes, and SMS alerts. It is built by two parents in Sonoma County, California, who got tired of guessing whether it was safe to send the kids outside. Why we built it
Go deeper
Air quality near Seattle
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