California cities top an unfortunate list—the nation's worst places to breathe. The Golden State claimed all five of the top slots for the highest air pollution in the American Lung Association's 2014 State of the Air Report. Sadly, the report was nothing new. Los Angeles, and cities in the San Joaquin Valley like Bakersfield and Fresno, have been in the top five since the ALA started its annual reporting in 2000.
Of particular concern is the continuing problem of fine particle pollution in these cities. Fine particle pollution consists of tiny, dirty motes—less than 1/30 the width of a human hair—that come from sources like diesel exhaust, agricultural activities, and burning wood or fossil fuels. These particles can be easily inhaled deep into the lungs and even absorbed into the bloodstream where they can cause a host of negative health impacts, including heart and lung disease, and asthma. So these areas aren't just the nation's most polluted, they are also some of the unhealthiest. Read more: