Why Seattle’s air quality is the worst in the world for two days in a row


SEATTLE — Seattle had some of the worst air quality in the world on Thursday, with thick fog and smoke obscuring the horizon, surrounding mountains and the Space Needle.

It was the second day in a row that the city had the worst air quality on the planet, beating heavily polluted cities such as Beijing and Delhi. Seattle’s Air Quality Index (AQI) reached above 240 on Wednesday and Thursday — a level defined as “very unhealthy” for all groups. It was difficult to see the tops of buildings a block away, and people wore masks to protect themselves from airborne particles and the pungent smell of smoke.

The concentration of PM 2.5 (tiny particles less than 2.5 micrometers in width) in Seattle on Thursday afternoon was 38 times higher than the annual guideline recommended by the World Health Organization, according to air quality monitoring site IQAir.

The reason is the wildfires raging in the Cascade Mountains, combined with weeks of unusually dry and hot weather. On Sunday, Seattle shattered its record for the hottest day of the year in late fall, reaching 88 degrees. Washington has seen little rainfall since June. According to the National Oceanic and Atmospheric Administration, 56 percent of the state is in drought.

Seattle’s air quality is the worst in the world, a “shocking statistic,” said Maddie Crystal, a meteorologist with the National Weather Service in Seattle. Part of the problem, she explained, was the persistent ridge of high pressure that kept the storm from falling over Seattle.

“That ridge is really solid, it just doesn’t allow differences in weather patterns to pass through,” she said. Combined with the higher-than-normal temperatures, the fires were burning longer than they would otherwise have been.

The city’s horrific air comes as researchers try to understand whether wildfire smoke is worsening — and how it’s affecting human health on the West Coast and beyond. The number of people in the U.S. experiencing extreme smoking days has increased significantly over the past decade, according to a study published last month.

“Intuitively, if you live in the West, you know things have changed, it’s become more smoky,” said Marshall Burke, a professor of geosciences at Stanford University and one of the study’s co-authors. “But our goal is to try to quantify how much.”

The researchers found that from 2006 to 2010, fewer than 500,000 people were exposed to extreme levels of PM2.5 on a daily basis each year. But between 2016 and 2020, that number climbed to more than 8 million. Hotter, drier climates—combined with failure to plan and enforce prescribed burns that could prevent huge wildfires—have led to an increase in the number of Americans exposed to suffocating, acrid air in the summer and fall.

Researchers know PM2.5 is extremely bad for human health — it increases breathing and Cardiovascular problems, and frequent high exposures Has been shown to affect cognition and test scores in children. But, Burke said, no one really knows how brief spikes in extremely high air pollution affect health and cognition.

Staying indoors doesn’t necessarily solve the problem: Many indoor air sensors in Seattle on Thursday reported an air quality index between 100 and 150, which can be dangerous for many vulnerable populations, according to the air quality monitoring site PurpleAir.

Faced with poor air quality, Burke recommends staying indoors, closing doors and windows, and using an air purifier or other filtration system whenever possible. Those without an air purifier can make so-called “Corsi-Rosenthal boxes” or box fans with air filters for a quick DIY solution for cleaning indoor air.

Ultimately, however, researchers are only just beginning to scratch the surface of a fire-filled climate future. Poor air quality “affects our lives in many ways,” Burke said. “We’re just beginning to understand how important it is.”

An air quality alert in effect in Seattle is set to expire Friday morning. Rain is expected Friday afternoon through Saturday, and the National Weather Service said the system should “help further improve air quality.”

Jason Samenow contributed reporting

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