Triple-digit temperatures and stubborn smoke from wildfires raging in British Columbia and parts of Oregon are joining forces to make Portland's air quality among the worst in the country this week.

Portland's Air Quality Index, the national standard used to measure the health effects of various pollutants, hovered in the high 170s throughout Thursday, according to the state's environmental quality department. Those levels exceeded air pollution in Beijing, according to a website that compiles air quality in dozens of countries.

State health officials issued an advisory Wednesday urging Oregonians throughout the Willamette Valley to take caution before going outside.

"People with chronic lung or heart conditions, the elderly, and children have higher risk of health problems from the fine particles in wildfire smoke," Dr. Richard Leman, a state public health physician, said in a statement. "People who suffer from asthma or other respiratory conditions should follow their disease management plans, keep medications on hand, and contact health care providers if necessary."

The poor air quality extends throughout much of the Willamette Valley and into Southwest Washington. The Southwest Clean Air Agency, which enforces air quality laws in Washington, issued air pollution advisories for Clark, Cowlitz, Lewis, Skamania and Wahkiakum counties.

Air quality has only worsened since Oregon issued its warning Wednesday.

"That's not good," Greg Svelund, a spokesman with Oregon's Department of Environmental Quality, said of Portland's air quality. "There's no way around it."

Portland's parks bureau opted to close its outdoor pools on Thursday and Friday in response to air quality concerns.

Svelund added that it's unusual for Portland to have the worst air quality in the state during wildfire season. Central and Southern Oregon typically take the brunt of wildfire smoke.

But Svelund said the air pollution woes are not completely out of the ordinary.

"Every couple of years, Portland gets whacked," he said, "and it looks like now is their turn."

A DEQ map shows air quality index readings in Oregon on Aug. 3, 2017.

In 2015, it was also Portland's turn to suffer from a lingering blanket of wildfire smoke, which carries harmful particulates that can be hazardous. Strong winds blew smoke from blazes in the Columbia River gorge into the metro area, prompting several days of air quality levels in the more serious "hazardous" range.

Federal standards describe Portland's current air quality range as "unhealthy" and caution "everyone may begin to experience health effects," while young people, the elderly, pregnant women and other sensitive groups could experience more serious health setbacks.

Wildfires and scorching temperatures are expected to stick around through much of next week. The Washington advisory estimates that air quality could stay poor until Aug. 8.

David Bishop, a meteorologist with the National Weather Service in Portland, said the agency is bracing for two different scenarios. One model projects winds could push smoke out of the area as soon as Friday.

The other scenario foresees smoke in the area until early next week.

This post has been modified to correct the spelling of Greg Svelund's name.

-- Andrew Theen

atheen@oregonian.com

503-294-4026

@andrewtheen