In L.A., Pollution is Down Dramatically but Bad Air Remains

The recent paper, published in the Journal of Geophysical Research, shows a dramatic 98 percent drop in air pollution from motor vehicles since the 1960s, despite a threefold increase in the use of gasoline and diesel fuel over the same period. The chemicals tracked by the researchers, called volatile organic compounds (VOCs), are primarily emitted from the tailpipes of vehicles, and "are a key
ingredient in the formation of ground-level ozone," writes the National Oceanic and Atmospheric Administration. 

"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," said Carsten Warneke, Ph.D., a NOAA-funded scientist with the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder. "The difference was amazing."

Despite the improvements in vehicle emissions, attributed to "requirements for catalytic converters, use of reformulated fuels less
prone to evaporate, and improved engine efficiency of new vehicles," overall ozone levels in L.A. have not fallen as steeply. "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."