The American Lung Association released the State of the Air 2012 today, an annual report on air quality which lists both the cleanest and most polluted areas in the country. This year's report shows that although California still has some of the worst air in the nation, continuous progress in reducing ozone and particulate pollution has resulted in the state's air quality at its cleanest since the Lung Association's annual report began 13 years ago.

"This report shows that air pollution remains a serious health threat to too many Californians," says Jane Warner, President and CEO of the American Lung Association in California. "State of the Air 2012 shows that we're making real and steady progress in the fight for clean air, but unhealthy levels of air pollution still exist, putting the health of millions Californians at risk.  Much still needs to be done, and now is not the time to stop progress."

More than 90% of Californians live in counties plagued with unhealthy air, particularly in the Central Valley, Los Angeles, Inland Empire, Sacramento, and San Diego. That means more people are at risk for asthma attacks, heart attacks, and premature death. California cities once again dominate lists for the top ten most polluted areas in the nation for ozone (smog) and short-term and annual particle pollution. Specifically, of the top ten cities with the worst air pollution, California ranks as follows:

Despite these poor rankings, many California cities continue to show improvements, including reductions in unhealthy ozone and particulate pollution. The Los Angeles region shows particularly noteworthy success in reducing particle pollution over the years of the State of the Air report. Annual levels of particle pollution have dropped by over 40% throughout the region and the number of days for short-term particle pollution has dropped by 53% since the State of the Air report began collecting this data, with some annual fluctuations.  California's groundbreaking air quality policies such as the advanced pollution standards on cars and fuels and diesel emissions regulations implemented by the California Air Resources Board (CARB) have been responsible for tremendous progress in reducing the ozone pollution and diesel soot harming California residents.

Air pollution problems not only originate within urbanized areas but are also transported to other areas of the state.  For example, in the San Luis Obispo area, air pollution transported from nearby areas is a primary culprit for poor air quality grades, demonstrating that air pollution is a regional problem.

California's pollution problems are primarily caused by emissions from mobile sources like cars, diesel trucks and buses, locomotives, ships, agricultural and construction equipment, and other transportation sources.  Oil refineries, manufacturing plants, and residential wood burning also are key sources of emissions. In addition, California's warm climate promotes the formation of ozone pollution, and valleys and mountains in the central and eastern portions of the state trap pollution where it can linger for days and put residents at risk for the onset or exacerbation of lung disease.

"Ozone and particle pollution contribute to thousands of hospitalizations, emergency room visits, and deaths every year," says Kari Nadeau, MD, PHD, associated professor of immunology and allergy at Stanford Medical School and an American Lung Association researcher. "Air pollution can stunt the lung development of children, and cause health emergencies, especially for people suffering from chronic lung disease including asthma, chronic bronchitis, and emphysema.  Both long-term and short-term exposures can result in serious health impacts.  Cleaner air can save lives and can lead to better lives for our children."