If you have declined to wear a face mask during the COVID-19 crisis, you might want to reconsider, as the smoke from over 300 wildfires chokes people across central and Northern California.
But you are going to have to think a little more about what kind of mask is best.
The fires have spewed toxic substances far and wide, raining ash across the region and leaving an acrid brownish-gray haze. Air quality in much of the Bay Area was the worst in the world for a few days last week. And fire season is only just beginning.
The biggest health risk: tiny particles, less than 2.5 microns in diameter, that make up 80% of wildfire smoke. They can enter the bloodstream through the lungs, damaging