Regulating Diesel Emissions: An Environmental Twofer

Peter Fimrite writes about that the three-year study, funded by the California Air Resources Board (CARB) that examined the effectiveness of diesel emission regulations in reducing emissions of black carbon, a major contributor to climate change. CARB has been regulating tailpipe emissions since 1967 to protect public health. Strict, controversial regulations for trucks and buses were approved in December, 2008 and reported here. This study shows how diesel emission regulations protect both climate and health.

The study 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. ......

Unlike carbon dioxide, the main contributor to climate change which by itself is a harmless gas, black carbon emitted from diesel exhaust poses a serious threat to public health.

• Diesel particulate matter poses a major threat to the respiratory system.
• Diesel exhaust is consider a toxic airborne emission, along with formaldehyde and benzene, that are emitted by motor vehicles that pose cancer risks.
• "EPA has concluded that diesel exhaust is among substances that may pose the greatest risk to the U.S. population," the agency said. (NYT)

In addition to causing health problems, black carbon has been identified as the second-largest contributor to global warming behind carbon dioxide, writes Fimrite, and reported here on January 18.

"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 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. 

From executive summary (PDF, pg. 20): 

Black Carbon emission reductions since the 1980s, attributed in large part to diesel engine emissions mitigation, are equivalent to reducing CO2 emissions by 21 million metric tons annually. This is approximately equal to 5 % of the total direct CO2 annual emissions of 393 million metric tons.

From Scripps news release: 

“We know that California’s programs to reduce emissions from diesel engines have helped clean up the air and protect public health,” said ARB Chairman Mary D. Nichols. “This report makes it clear that our efforts to clean up the trucks and buses on our roads and highways also help us in the fight against climate change.”

The U.S. Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) and Pacific Northwest National Laboratory also participated in the study.

The study should help the Air Resources Board as it sets out to implement rigorous regulations to reduce diesel emissions from trucks and buses. In addition, for policy makers who are skeptical of climate change, the public health benefits of reducing black carbon might prove less controversial.