Air quality deteriorated rapidly Monday morning, reaching levels that impacts everyone's health, by federal standards. For sensitive groups, those effects may be serious.

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The National Weather Service in Seattle has issued an Air Quality Alert for Western Washington, after wildfire smoke returned to the Puget Sound area.

Monitoring stations in the Seattle region were reporting air-quality ratings from moderate to unhealthy Monday morning. Air quality will worsen in the late morning and early afternoon Monday, likely reaching unhealthy levels throughout the region, National Weather Service meteorologist Andy Haner said. The air-quality advisory runs through 5 p.m. Wednesday.

[ Smoky Seattle summers: Expect more of them, scientists say ]

The pollution may start lifting Monday night, Haner said, but residents should expect to see smoke-filled skies until fresh ocean air enters the region Thursday, bringing more widespread improvement.

“We’re going to keep some amount of smoke in the Seattle area through Wednesday,” Haner said.

Thick smoke from wildfires raging in British Columbia has caused delays at Seattle-Tacoma International Airport, according to the Federal Aviation Administration. The FAA has been conducting traffic management to keep planes further apart in the air due to low visibility from the smoke, airport spokesperson Perry Cooper said.

“It’s not affecting everybody,” Cooper said. “But it’s worse than normal.”

Travelers should check in with their airlines and sign up for flight alerts, which can be done on airline websites or through the Port of Seattle, Cooper said.

Shifting winds will bring wildfire smoke from Eastern Washington, rather than British Columbia, into the region on Tuesday, Haner said.

High winds and low humidity may contribute to igniting wildfires to start the week, the weather service said on its website.

Those with heart or lung disease, older adults and children should avoid “prolonged or heavy exertion” and outdoor activities, according to Airnow.gov, a website developed by federal and local government agencies to monitor air quality. The website’s air-quality index, which measures levels of the most harmful particulate matter in the air, posted a reading of 161 in the wider Seattle area as of noon Monday. By federal standards, that’s a level that impacts everyone’s health, especially sensitive groups. However, the air quality throughout the region varies, with Seattle’s air mostly in the moderate category.

The gauge would need to fall to below 50 in order for air quality to be considered good.

People who are sensitive to poor air quality may experience symptoms of itchy, irritated eyes, sore throats and coughs.

In Washington state this year, 13 large wildfires have burned more than 211 square miles. In Seattle last week, air quality was worse than in some of the world’s most polluted cities.

2018 marks one of the hottest and driest summers on record for the Puget Sound area. Researchers predict the region will experience more smoky weeks in coming years.