An air stagnation advisory issued Tuesday across the Inland Northwest prompted an outdoor burning ban in North Idaho and put Washington officials on alert for pollution.
The Idaho ban was in effect for Boundary, Bonner, Kootenai, Shoshone and Benewah counties. Residents were also asked to refrain from indoor burning until ventilation improves.
The U.S. Environmental Protection Agency ordered outdoor burn bans on Indian reservations across the Pacific Northwest on Tuesday.
The National Weather Service said it expected pollution to rise to dangerous levels through Sunday afternoon under a temperature inversion.
At the Spokane Regional Clean Air Agency, officials were expected to consider a burn ban this morning.
Ron Edgar, chief of technical services, said a stage-one ban was possible if pollution levels rise into the moderate range today, as expected. A stage-one ban means only certified wood stoves can be used indoors. Residents with fireplaces and non-certified stoves must allow fires to go out unless that is they are their only heat sources.
The last such ban in Spokane was Nov. 21-26, 2007.
The Washington Department of Ecology had not imposed any burn bans for rural counties as of Tuesday.
Air quality in Kootenai and Spokane counties was in the good range Tuesday but had deteriorated since Monday.
High pressure over the region was expected to allow cooler air to pool along the ground. Air normally gets colder with elevation, but under an inversion, the air aloft can be markedly warmer.
While stratus clouds and fog are expected in the lowlands through Sunday, highs above the stratus layer at an elevation of about 3,500 feet could reach into the 40s, and skies should be sunny, forecasters said.
The cooler air on the ground becomes trapped under the warmer air so that pollution cannot be diluted through wind- or temperature-driven mixing. Smoke particles were expected to be the main pollutant.
Temperatures for the area will remain seasonal, with highs and lows both in the low to mid-30s. The difference between day and night temperatures often is only a couple of degrees when low clouds and fog settle over the region under an inversion.
A dense fog advisory was lifted for the Spokane area but remained in effect for the Moses Lake area Tuesday.