Wildfires bring unhealthiest air in the nation to Southern California

A pair of wind-driven wildfires actively burning in Orange County and a couple of nearly extinguished blazes in Los Angeles and San Bernardino counties have spawned the worst air quality in the nation, according to the government's air quality monitoring agency.

Parts of Los Angeles and Orange counties and the city of Corona are all hovering in the "unhealthy" range, the website Air Now shows.

On Tuesday, the South Coast Air Quality Management District issued a windblown dust and ash advisory in Los Angeles, Orange, San Bernardino and Riverside counties, warning that hazardous particulate matter from recent wildfires may be spread by strong gusts of wind.

It is an atypical warning for L.A. and Orange counties, said agency spokesman Bradley Whitaker.

"Sometimes we'll issue windblown dust advisories in Coachella Valley," Whitaker said. "It's a bit more rare in L.A. County and Orange County."

Whitaker said ash plumes — not smoke plumes — could be seen on satellite imagery Monday.

"That's why we put out the extended dust advisory," he said.

The resulting air quality index reached unhealthy to hazardous levels because of particulate matter, the agency said.

The advisory, which remains in effect through Tuesday evening, said that sand, dust and ash are being carried from the scars of past blazes, including the Bobcat and El Dorado fires. Angeles National Forest spokesman Andrew Mitchell said wind-blown dust and ash from the Bobcat fire will remain a possibility until rain eventually comes and helps with "dust abatement."

Active fires are making it hard to breathe too. Smoke advisories are in effect in Orange County because of the ongoing Silverado and Blue Ridge fires, which erupted Monday and quickly burned through a combined 20,000 acres.

"The Silverado fire is producing substantial amounts of smoke," the air quality management district said, adding that residents should limit outdoor activity and remain indoors with windows and doors closed.

The latest air quality concerns follow months of orange skies and ash-dusted neighborhoods from California's worst wildfire season. In September, dozens of concurrent blazes across the state created a plume of smoke that spanned more than 1,000 miles and traveled as far as Europe.

Smoke — and its resulting hazardous air — has even spawned a new subfield of fire science: aeropyrobiology, which studies how fire-powered plumes can waft about landscapes, like "an atmospheric analogue to ocean currents."

This story originally appeared in Los Angeles Times.