May 23, 2008
California's smog and air pollution is legendary, and now a state agency warns it is also deadly. The California Air Resources Board has received research showing long-term exposure to fine-particle pollution pose a greater health threat than previously estimated.

According to the report, 14,000 to 24,000 premature deaths a year are estimated to be associated with exposures to PM2.5, a mix of microscopic particles less than 2.5 microns in size. A majority of these deaths occur in highly populated areas around the state, including the South Coast, San Joaquin Valley and San Francisco Bay air basins.

"Particle pollution is a silent killer," said ARB Chairman Mary D. Nichols. "We must work even harder to cut these life-shortening emissions by further addressing pollution sources head-on."

Particulate matter (PM) is a complex blend of substances ranging from dry solid fragments, solid-core fragments with liquid coatings, and small droplets of liquid. These particles vary in shape, size and chemical composition, and may include metals, soot, soil and dust.

At the request of the board in 2006, ARB researchers carefully reviewed all scientific studies on the subject and consulted with health scientists. While exposures to particulate matter have long been known as a serious health threat, new information suggests that the pollutant is even more toxic than previously thought.

Hospitalizations, emergency room visits and doctor visits for respiratory illnesses or heart disease have been associated with exposure to particulate matter. Other studies suggest that exposure may influence asthma symptoms and acute and chronic bronchitis.

Children, the elderly and people with pre-existing chronic disease are most at risk of experiencing adverse health effects. Even small increases in exposures may increase health risks.

Major contributors include trucks, passenger cars, off-road equipment, electric power generation and industrial processes, residential wood burning, and forest and agricultural burning. All combustion processes generally produce fine particulate matter.