Air Improves in Los Angeles Basin, but Not Enough

January 5, 2008

The Orange County Register

A regional study released Friday offers good news and bad news about cancer risk from toxic air contaminants.

The good news: The risk has dropped by 15 percent overall in the Los Angeles basin, which includes Orange County, since a previous study seven years before.

The bad news: That risk level is still considered far too high by scientists at the region's smog agency. In fact, it is likely to be the nation's highest.

Based on real-world measurements plugged into a computer model that spits out estimates of risk, 1,200 people out of 1 million would be expected to contract cancer, on average, during a lifetime of exposure to the L.A. basin's air.

The main culprit remains diesel exhaust, considered responsible for 84 percent of the total risk of cancer. Mobile pollution sources – cars, trucks and other vehicles – account for an estimated 94 percent of the risk.

The risk levels are "clearly too high, and unacceptable, relative to breathing air here in Southern California," said Barry Wallerstein, executive officer at the South Coast Air Quality Management District, which released the study. "The acceptable risk level is really down somewhere between one and 10 in a million."

Relying mainly on measurements from 10 permanent and five temporary monitoring stations throughout the four-county area regulated by the district, the study focused on 33 substances considered the biggest health threats in the basin's air – although there are hundreds of substances listed as toxic air contaminants.

The study's list included pollutants such as benzene from car exhaust, perchloroethylene from dry-cleaner's, and hexavalent chromium from chrome-plating operations.

The data, collected from April 2004 to March 2006, came from measurements taken every three days, with more than 18,000 air samples collected.

The study is known as MATES III, for Multiple Air Toxics Exposure Study. MATES II was released in 1999.

Smog regulators said two major initiatives are needed: first, intensified regulation of diesel engines, with increased pressure to convert to cleaner-burning engines before the end of a vehicle's life. Such "dirty" diesel engines include not only freight trucks, but "off-road" vehicles such as construction machinery, trains and ships at sea.

A second initiative would involve tighter regulation of all mobile pollution sources.

These fall under the jurisdiction of the state Air Resources Board. And while the air district's public pressure on the state agency to step up its efforts has led to strained relations in the past, Wallerstein said a new spirit of detente has flowered between the two that could lead to better cooperation.