With scores of wildfires burning across the Pacific Northwest and a gauzy pall hanging over much of Washington, air quality is reaching unhealthy levels on both sides of the Cascade Mountains.

According to the Washington Department of Ecology (DOE), the highest levels of particulate pollution from nearby fires were in the north-central Washington communities of Chelan and Omak, where the air was ranked as “very unhealthy.”

Conditions in most of Western Washington have improved since Tuesday, when air quality from Seattle and Bellevue to Tacoma and Chehalis was classified as “unhealthy.” But the National Weather Service on Wednesday issued an air quality alert and said smoke is likely to get worse in many areas through Thursday.

“It’s unusual and rare” to have such widespread smoke across the state, said Ranil Dhammapala, an atmospheric scientist with DOE’s Air Quality Program. “Today the winds have certainly died down, but there’s steady leakage of smoke from the eastern side of the mountains.”

Unfortunately, the cloth and surgical face masks that block respiratory droplets and help slow the spread of the novel coronavirus don’t provide much protection against wildfire smoke. The tiniest soot particles — which are less than 2.5 microns, or millionths of a meter, across — can pass through woven fabric, said UW Medicine pulmonologist Dr. Cora Sack.

“What we really worry about in wood smoke are those small particles, which, when inhaled, have the ability to get deeper into the lungs.”

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The coveted N95 masks do provide an effective barrier against fine particles, but they’re in short supply and should generally be reserved for health care workers. They also don’t filter out toxic gases, like carbon monoxide, in wood smoke.

Breathing in wildfire smoke can cause respiratory irritation and exacerbate existing conditions, especially in people with asthma, emphysema, chronic obstructive pulmonary disease, heart disease, diabetes or other health problems. It can also be especially hard on young children, people age 65 and older, and pregnant women.

The groups of people most at risk from wildlife smoke overlap many of the groups that are also at high risk for COVID-19, which compounds the danger, Sack said. There’s clear evidence that smoke exposure can lower immune defenses and increase the risk of influenza and other respiratory infections, she added.

“There have been some suggestions it might increase the risk of COVID-19, but we don’t have great data,” Sack said.

One of her patients with cystic fibrosis, who had to be hospitalized this week, blames the smoke for worsening her condition. Another, with emphysema, had to increase his inhaler usage.

For people with no underlying conditions, moderate exposure isn’t likely to cause serious problems, Sack said. “It’s OK to go about your normal activities. Just listen to your body and if you start having problems, go inside.”

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At a time when concern about COVID-19 has people spending more time outdoors where the risk of infection is lower, the advice for avoiding smoke exposure is just the opposite: Stay indoors.

Sack advises monitoring the Washington Smoke blog (https://wasmoke.blogspot.com) for daily updates and forecasts, and avoiding strenuous outdoor exercise when air quality begins to edge into the “unhealthy” range.

If you have an air conditioner, HEPA filters can help keep the smoke out of your house, Dhammapala said. Air purifiers are another alternative, as long as they are certified ozone-free.

Some people even create a “clean room” in their house, closed off from outside air and equipped with a portable air cleaner.  

With hot temperatures expected over the next few days, the best way to stay cool and also avoid smoke is to open your house at night or early morning to let cool air in, then close it up, draw the blinds or curtains and use fans for circulation.

“Heat stroke plus smoke inhalation is a bad combination,” Dhammapala said. “You need to do what it takes to safeguard your health from both of those.”

By Friday, the National Weather Service forecasts that the circulation pattern will shift, allowing cooler, onshore winds to dominate and help keep most of the smoke east of the Cascades.

But smoke from fires in Oregon and California could begin creeping into Southwest Washington beginning Thursday night and into Friday, said a DOE spokesperson. It’s not clear yet whether that smoke will mix down to the surface where it can affect people’s health and whether it will reach the Seattle area.