ildfires have broken out in Mexico over the past week, sending plumes of smoke drifting far beyond the burn sites to blanket population centers, including Mexico City, home to 21 million people.
Officials in Mexico City have declared a state of emergency and are urging people to stay indoors, as pollution levels soar far above what’s considered healthy for human exposure. Concentrations of PM2.5—tiny particulate matter produced during any combustion, like burning trees and plants during fires—reached 158 micrograms per cubic meter yesterday.
PM2.5 concentrations can be translated to cigarette equivalencies. According to analysis co-authored by Richard Muller, a physics professor at the University of California, Berkeley, if you were, on average, exposed to 22 micrograms per cubic meter of PM2.5, it’d be the equivalent to smoking one cigarette a day. So if you divide the concentration of PM2.5 by 22, you get the rough cigarette equivalence of simply breathing your region’s air.