Fogbow

SEATTLE — Seattle had the worst air quality in the world Thursday, with a heavy mix of fog and smoke blotting out the horizon, the surrounding mountains and the Space Needle.

It was the second day in a row that the city had the worst air quality on earth, beating out famously polluted cities such as Beijing and Delhi. Seattle’s air quality index, or AQI, reached over 240 on Wednesday and Thursday — a level defined as “very unhealthy” for all groups. It was hard to see the top of a building a block away, and people wore masks to protect themselves from particulates in the air and the acrid smell of smoke.
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According to the air quality monitoring site IQAir, Seattle’s concentration of PM 2.5 — tiny particles less than 2.5 microns in width — on Thursday afternoon was 38 times higher than the annual guideline recommended by the World Health Organization.

The cause was forest fires raging in the Cascade Mountains, combined with weeks of unusually dry and hot weather. On Sunday, Seattle broke a record for the hottest day this late in the fall, at 88 degrees. Washington has experienced precious little precipitation since June; 56 percent of the state is in drought, according to the National Oceanic and Atmospheric Administration.