The American Lung Association just released the 2007 State of the Air, an annual report examining air pollution levels in American cities and counties. The three principal reporting categories include short-term particle pollution (24-hour PM_2.5), year-round particle pollution (Annual PM_2.5), and ozone content. This year’s dishonor for most polluted city goes to the Los Angeles metro (includes Long Beach and Riverside), which leads U.S. cities in all three categories. This is not surprising, given the pervasive orange-gray blanket over the Los Angeles sky. Interestingly, despite strict emission laws, several other Californian cities and counties rank very highly in the list. Detroit (Michigan), home to the automotive industry, shares fourth place with Birmingham, Alabama.

As for the cleanest cities, Cheyenne (Wyoming) was ranked the best for long-term particle pollution, followed by Santa Fe (New Mexico) and Honolulu (Hawaii). To be fair to California, three of its cities (Salinas, Redding, and San Luis Obispo) were included in the top 25.