Emission cuts lead to cleaner Calif. air

In this file photo, traffic jams up on eastbound 91 freeway near Corona, Calif.

In this file photo, traffic jams up on eastbound 91 freeway near Corona, Calif. Photo: Bruce Chambers, Associated Press Photo: Bruce Chambers, Associated Press Image 1 of / 4 Caption Close Emission cuts lead to cleaner Calif. air 1 / 4 Back to Gallery

Cuts in diesel emissions have drastically reduced the amount of pollutants in the air that cause global warming in California, potentially valuable information in the fight to save the world's climate from a predicted catastrophe, a study by University of California and government researchers said Wednesday.

The study found that regulations limiting emissions from diesel-powered trucks, buses and off-road vehicles have taken the equivalent of 4 million cars off California roads every year since the late 1980s.

"We are all breathing cleaner air because of regulations in diesel combustion, but this study shows there was a huge co-benefit of mitigating climate change," said the lead researcher, Veerabhadran Ramanathan, a scientist with the Scripps Institution of Oceanography and UC San Diego. "I'm now very, very interested in taking this message to the rest of the planet, because if the California experience can be replicated around the world, then we can make a substantial dent in climate change."

The study, paid for by the California Air Resources Board, was the first regional assessment of the effect on the atmosphere of black carbon, the soot particles from burning diesel fuel. Black carbon is the primary ingredient in smog, the clouds of soot that for decades turned the air in Los Angeles and other places brown.

Besides causing health problems, black carbon has been identified as the second-largest contributor to global warming behind carbon dioxide.

Tailpipe emissions have been regulated in California since 1967, when the Air Resources Board was established. Diesel truck engines today are about 90 percent cleaner than the models used before emissions were regulated.

Ramanathan and his team of researchers from UC Berkeley, the Lawrence Berkeley National Laboratory and the Pacific Northwest National Laboratory in Richland, Wash., analyzed measurements of black carbon taken from aircraft, satellites and ground monitors dating back to the 1980s, and used a computer model to compare them with emission-reduction regulations that the state issued over the years.

Ramanathan said the reductions in warming pollutants were much more dramatic than expected. The clean air regulations, he said, removed the equivalent of 21 million tons a year of carbon dioxide from the atmosphere - the amount spewed by 4 million cars.

Over the past 45 years, the total level of black carbon in California's air has decreased about 90 percent while diesel fuel consumption has quintupled, according to the study.

The findings could serve as ammunition for the state as it moves forward with plans to stiffen emissions rules for trucks and buses. Engine emissions control systems and filters are being developed that could reduce exhaust pollution even further.

"The message, particularly for metropolitan areas in California, is that if you clean up the air to improve air quality you will also protect climate," Ramanathan said. "It is a hopeful message because, in the area of climate mitigation, we have gotten into a funk. But now we know we can do something about it."