The sprawling city -- a metropolitan area of more than 20 million people -- has been blanketed in a thick cloud of smog since last weekend. Mexico City is prone to air pollution, both because of the mountains that surround it -- trapping smog overhead -- and its more than five million cars. Authorities declared a pollution alert from Tuesday to Friday, after the micro-particle level hit 158 micrograms per cubic meter. But breathing the air was still equivalent to smoking nearly five cigarettes a day, according to the 2015 study, which compared deaths from air pollution and smoking. The "goal of this calculation is to help give people an appreciation for the health effects of air pollution," the Mullers wrote.

Source: The Nation Bangkok May 18, 2019 05:03 UTC