Parched vegetation combined with strong Santa Ana winds and low relative humidity levels led to the devastating wildfires in Los Angeles County.

Winds have begun shifting to the east, which drove the Eaton fire toward Arcadia and Monrovia early Wednesday morning. Smoke will more likely begin to blow into the eastern San Gabriel Valley, not as much to the south of the fire, Lyou explained. “Arcadia, Duarte and Azusa may see elevated levels (of bad air) from that fire,” he said.

Southern California — with sprawling cities, clogged freeways and heavy industry — is already notorious for some of the worst air quality in the nation. This week's wildfires are putting millions of people at risk for immediate health problems and longer term issues.