MEXICO CITY, MEXICO - APRIL 5: A man rides a bike wearing a mask on April 5, 2016. in Mexico City, Mexico. According to authorities have declared a pollution alert after smog rose to 1and a half times acceptable limits on the eve of an unpopular new program to reduce the number of cars on the road in hopes of improving the capital's dirty air. (Photo by Miguel Tovar/LatinContent via Getty Images)