For that reason Forbes focused on the metros most affected by year-round particle pollution for this list. The ALA compiled a list of the 10 worst culprits. (A total of 11 metros made the list due to a tie in the data.) Many major urban hubs in the Golden State ranked high on the list, but one other southwestern U.S. city tied Los Angeles for second place: Phoenix, Ariz. Like California's hardest-hit cities, the foreclosure mecca's climate and geography serve as incubators for airborne toxins. But one of the biggest reasons for Phoenix's high pollution levels is actually cattle ranches found south of the city, in Pinal County and vicinity.. "Those cattle ranches are contributing a lot of fine particle pollution to the small communities near them that are part of the Phoenix metro area, but also to the tribe adjacent to it," says Nolen. "It's also being blown into other parts of the city."
Closer to the east coast, Pittsburgh, Pa., has long been associated with coal, and it shows in the numbers. The Steel City ranks seventh on the list of most polluted, followed by another metro chock-full of coal-fired power plants: Birmingham, Ala.
Nolen says air pollution can cause asthma attacks, heart attacks, strokes, lung conditions and difficulty breathing for some people. California, for example, estimates that 9,000 people die each year from air pollution-related illnesses.
"We have a lot of folks that see this report and call up and ask 'where should I go?'" says Nolen. "We want people to do things like check the Air Quality Index. If it's going to be a very unhealthy day, you can take steps to avoid exercising outside or working outdoors strenuously." She also adds that people should avoid running within 300 to 500 meters of major roads, which tend to have elevated levels of air pollution.
The good news is that most metros and counties around the country have been improving their air quality, thanks in part to support from the EPA and the implementation, albeit slow, of the 1990 Clean Air Act. Most cities that topped the ALA's most polluted lists for particle and ozone pollution have seen their levels decrease. The only city in the top 10 to actually get worse in terms of year-round particle pollution levels was Bakersfield.