DENVER — For decades America’s air was getting cleaner as levels of a key smog ingredient steadily dropped. This means when tighter federal air quality standards go into effect later this year, many more cities may find themselves on the dirty air list. The study, in Monday’s Proceedings of the National Academy of Sciences, used satellite and ground measurements to track nitrogen oxides, a major ingredient in smog. In 2015, the EPA proposed new air quality standards limiting smog levels to 70 parts per billion, down from the current 75 parts per billion. If smog levels were high, “it would really make my lungs burn,” she said.

Source: National Post April 30, 2018 19:05 UTC