A new American Lung Association report cites two of California’s urban areas as America’s worst polluted areas. Bakersfield topped the list, having the most unhealthy days due to particle pollution, which comes from heavy traffic, diesel trucks, and farm equipment, while Los Angeles remained the No. 1 city for harmful ozone pollution. The annual “State of the Air” report, which collected data from 2012 to 2014, also found about 52 percent of the population—166 million Americans—lives in the 418 counties where they’re exposed to unhealthful pollution levels. The figure is a marked increase from last year’s report, which only found four in 10 Americans, or about 138.5 million people, living in such conditions. High pollution levels can trigger asthma attacks, heart attacks, premature death, or cause lung cancer.