FILE - This Sept. 13, 1979, file photo shows motorists as downtown Los Angeles parking lots fill up in Los Angeles. A study appearing in the Thursday, March 5, 2015, issue of the New England Journal of Medicine says children in recent years breathed cleaner air and had stronger lungs compared to those who were studied two decades earlier, researchers found. For decades, the city struggled with air pollution. As LA's population grew, so did the number of vehicles on the road. In the 1970s, unhealthy air was recorded more than 200 days a year. (AP Photo/Wally Fong, File)