8 of the 10 most polluted US cities are located in California

There is no doubt that great strides have been made in air pollution in the U.S. Awareness, stricter legislation and improved technology have all contributed to improved air, land and water conditions. Despite the improvements, four in 10 Americans still live where pollution levels are often dangerous to breathe.

Since the American Lung Association began studying particle pollution, almost all of the most polluted cities have consistently remained among the worst. The ALA’s 2013 “State of the Air” report measures cities based on low-lying ozone pollution, as well as both short- and long-term particle pollution.

Based on average long-term particle pollution figures collected by the ALA between 2009 and 2011, 24/7 Wall St. identified the 10 most polluted cities in the country. For each of these metropolitan areas, the ALA noted the population and the number of people in the area with health problems that high pollution can exacerbate, such as asthma and cardiovascular disease.

Check out the 10 most polluted US cities, 8 are in California: