Oregon and Southwest Washington officials are issuing an advisory against wood-burning because stagnant air conditions in the region.

The advisory is in place for the Willamette Valley, the Columbia River Gorge, Central Oregon and Southwest Washington.

Stagnant air conditions are trapping woodsmoke-below 1,500 feet. That means too many tiny particles from wood-burning are lingering near the ground where people breathe.

“Inversions trap wood smoke and other air pollutants near the ground by acting as a ‘lid’ that prevents pollution near the surface from mixing with clean air higher in the atmosphere,” Oregon Department of Environmental Quality’s Lauren Wirtis said. “They are a fairly common wintertime phenomenon and can lead to high air pollution concentrations when they persist for several days.”

The Oregon DEQ is asking people to protect their health by avoiding excess outdoor activity and avoid wood-burning stoves.

The department expects the air quality advisory to last through Friday. 

An earlier wood-burning ban in Multnomah County was changed at noon Wednesday to a voluntary burn restriction.