Californians Dying Prematurely from Particles in Vehicle Exhaust

A majority of these deaths occur in highly populated areas around the state, including the South Coast, the San Joaquin Valley and the San Francisco Bay air basins.

All combustion processes produce fine particles. Major emitters include trucks, passenger cars, off-road equipment, electric power generation and industrial processes, and residential wood burning, as well as forest and agricultural burning.

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

At the request of the Air Resources Board in 2006, staff researchers 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.

The premature deaths are associated with exposures to PM2.5, a mix of microscopic particles less than 2.5 microns in size, the research report shows.

Traffic crawls along a street in San Francisco's Chinatown, emitting fine particulate matter. (Photo by Michael Vu)

Hospitalizations, emergency room visits and doctor visits for respiratory illnesses or heart disease have been associated with PM2.5 exposure. Other studies suggest that PM2.5 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 from PM2.5 exposure. The report shows that even small increases in PM2.5 exposures may increase health risks.

While the new data reveals a greater threat from fine particle pollution, the state's previous efforts to reduce emissions throughout the state have been successful, the ARB said Thursday.

Since the official year-round monitoring of PM2.5 in the air began in 1999, the board says concentrations have decreased 30 percent across California, most notably in the South Coast and the San Joaquin Valley regions.

In 2000, the ARB adopted a risk reduction plan that targets all diesel sources of particulate matter in California. As part of the plan, cleaner diesel fuels and new diesel engines have been developed for both on-road and off-road uses.

Other regulations have been adopted to address diesel engines already on the road, including those in waste collection vehicles, transit fleet, school buses, stationary engines, transport refrigeration units and portable engines.

Later this year, the ARB will consider rules to cut diesel particulate emissions from private truck fleets.

The process that produced the draft report submitted to the Air Resources Board on Thursday began in 2006 when staff was directed by the board to update the health impacts methodology to reflect recent health information on PM2.5 exposures and premature death.

A formal review of the updated methodology and analysis was conducted by a peer review committee formed by the University of California composed of experts in the fields of epidemiology, air quality measurement, risk management, health effects of air pollution, and biostatistics.

The draft staff report was discussed at Thursday's Air Resources Board meeting and is now available for public comment. Public input will be considered in drafting the final report, due for release to the public in August.

To view the report, "Methodology for Estimating Premature Deaths Associated with Long-term Exposures to Fine Airborne Particulate Matter in California," click here.

Submit comments on the draft staff report to lead author Dr. Hien Tran by email at htran@arb.ca.gov or by fax at: 916-323-1045 or 916-322-4357 by July 11, 2008.

Comments may also be mailed to Dr. Tran at the Air Resources Board, Research Division, 1001 I Street, P.O. Box 2815, Sacramento CA 95812.

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