Wildfire smoke is a mixture of water vapor, gases, and microscopic particles known as particulate matter. The smallest of these particles, known as PM2.5 because they have a diameter of less than 2.5 micrometers, pose the most danger to human health. They can lodge deep in the lungs and sometimes enter the bloodstream. Earlier this week, PM2.5 around Los Angeles rose to “hazardous” levels, the highest warning on the US Air Quality Index . “Wildfire smoke is risky for everybody, especially when...
