By Jim Taylor, Editor MACS ACtion Magazine
In California’s Los Angeles Basin, levels of some vehicle-related air pollutants have decreased by about 98 percent since the 1960s, even as area residents now burn three times as much gasoline and diesel fuel. Between 2002 and 2010 alone, the concentration of air pollutants called volatile organic compounds (VOCs) dropped by half, according to a new study by NOAA scientists and colleagues, recently published in the Journal of Geophysical Research.
VOCs, emitted from the tailpipes of vehicles and other sources, are a key ingredient in the formation of ground-level ozone which, at high concentrations, can harm people’s lungs and damage crops and other plants. Researchers noted that a few specific VOCs, such as propane and ethane, did not drop as quickly. Those chemicals come from sources other than vehicles, and an earlier study has shown that one VOC, ethanol, is increasing in the atmosphere, consistent with its increasing use in transportation fuels.
However, the magnitude of the drop in VOC levels was surprising, even to researchers who expected some kind of decrease resulting from California’s longtime efforts to control vehicle pollution. “Even on the most polluted day during a research mission in 2010, we measured half the VOCs we had seen just eight years earlier,” Carsten Warneke, Ph.D., a NOAA-funded scientist said. “The difference was amazing.”
The study cited requirements for catalytic converters, use of reformulated fuels and improved engine efficiency as all likely contributors to declines in vehicle-related pollution. Dr. Warneke also said that he expects the decrease in emissions of VOCs by cars to continue in Los Angeles, given that engine efficiency continues to improve and older, more polluting vehicles drop out of the fleet.
But the 98 percent drop in VOCs in the last 50 years does not mean that ozone levels have dropped that steeply; the air chemistry that leads from VOCs to ozone is more complex than that. Ozone pollution in the Los Angeles Basin has decreased since the 1960s, but levels still don’t meet ozone standards set by the Environmental Protection Agency.
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