A recent artivle in the New York Times highlighted the pollution problems in California:

"Air pollution led to almost 30,000 hospital admissions and emergency room visits for asthma, pneumonia and other respiratory and cardiovascular ailments from 2005 to 2007. Three quarters of the complaints were related to fine particulate pollution, or small pieces of soot that get trapped in the lungs, and the remainder were caused by ozone."

http://greeninc.blogs.nytimes.com/2010/03/12/health-costs-of-california-air-pollution/