Seattle and Portland endure world's worst air quality as wildfires burn

SEATTLE — A string of wildfires darkened skies Wednesday and Thursday in the Pacific Northwest, where residents of the normally lush, green region experienced the world's worst air pollution.

Seattle and Portland, Oregon, were first and second, respectively, in the global ranking of places with the poorest air quality, according to IQAir, a Swiss company that measures air pollution.

The quality was worse than in places like Beijing, New Delhi and Lahore, Pakistan, which more frequently struggle with air pollution.

On Wednesday afternoon, the Puget Sound Clean Air Agency urged residents to stay indoors.

However, relief should be on its way soon, as a storm system is expected to move through through Seattle and the Cascade mountain range, dropping rain Friday and Saturday.

"We’re starting to get that October precipitation," said Kirby Cook, a National Weather Service meteorologist based in Seattle. "That fall precipitation will be the key to clean the fires out."

Seattle, a city known for its rainfall, hasn’t received any significant precipitation since June 9. This summer was the driest on record.

The Bolt Creek Fire is responsible for much of the current smoke near the city, as it has burned more than 14,000 acres to Seattle's east. The blaze, first reported Sept. 10 north of Skykomish, was listed at 41% contained Thursday.

Air quality issues have persisted for about a month because of the prolonged fires burning west of the Cascades.

"We can get smoke here in western Washington, but it’s usually coming from somewhere else," Cook said. "This year, the smoke we have in the area is literally from our own neighborhood. That’s what’s been contributing to the persistent air quality issues we’ve had."

Meanwhile, closer to Portland, the Nakia Creek Fire was 23% contained, with nearly 2,000 acres burned, officials said. The blaze was first reported Oct. 9 in Camas, Washington.

Sports and other outdoor activities in the Pacific Northwest have been called off due to the poor air quality.

Four boys soccer games and two girls matches were cancelled on Wednesday, according to the Oregon School Activities Association. At least one football game set for Thursday night has also been called off.

Casey Johnson, a spokesperson for the Washington Interscholastic Activities Association, said the group anticipates that local officials will call off a rash of games on Thursday.

"While our office doesn’t have specific information on which games were cancelled, or how many, there were certainly postponements and cancellations over the past week and will be more tonight with the current smoke status," Johnson said in statement.

Air pollution from wildfire smoke has become more prevalent and extreme in the U.S. According to a September study from Stanford University researchers, the number of people who experienced a day with unhealthy air quality rose 27-fold over the last decade.

The problem is worst in the West, where rising air pollution levels due to smoke have reversed decades of improvements in overall air quality.

Of particular concern to scientists are increases in the concentration of fine particles under 2.5 micrometers in diameter (less than 4% of the diameter of a human hair).

Such particles can penetrate deep into the lungs and enter the bloodstream. They may increase one's risk of asthma, lung cancer or other chronic lung diseases, particularly in vulnerable groups such as older people, pregnant people, infants and children.

Evan Bush and Lewis Kamb reported from Seattle, and David K. Li and Aria Bendix from New York City.

This article was originally published on NBCNews.com