As of 2015, some American cities with consistent levels of pollution include Los Angeles-Long Beach, Visalia-Porterville, Bakersfield-Delano, Fresno-Madera and Sacramento-Roseville. These cities are all located in the state of California.
Pollution level rankings are determined in three ways: short-term particulate matter, ozone levels and year-round particulate matter. The most polluted city based on short-term and long-term particulate matter is Bakersfield-Delano, while the city with the worst ozone levels is Los Angeles-Long Beach. From all three categories, Californian cities consistently rank in the top five most polluted cities, with Bakersfield-Delano, Fresno-Madera and Los Angeles-Long Beach as repeat offenders on all three lists.