California’s Los Angeles Basin has seen a radical drop in volatile organic compounds (VOCs), 98 percent over the past 50 years, despite residents of the area burning more than three times as much gasoline and diesel fuel as they did back in the 1960s.
“The reason is simple: Cars are getting cleaner,” 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 research was published in the Journal of Geophysical Research last week.
The magnitude of the drop in VOCs was a surprise even to the researchers who were expecting a drop of some sort to occur over the period of their research. Looking solely at the years between 2002 and 2010, the concentration of VOCs dropped by half!
“Even on the most polluted day during a research mission in 2010, we measured half the VOCs we had seen just eight years earlier,” Warneke said. “The difference was amazing.”
VOCs are primarily emitted from tailpipes of vehicles, and “are a key ingredient in the formation of ground-level ozone which, at high levels, can harm people’s lungs and damage crops and other plants,” said NOAA.
For the new study, Warneke and his colleagues evaluated Los Angeles air quality measurements from three sources: NOAA-led research campaigns in 2002 and 2010, which involved extensive aircraft sampling of the atmosphere; datasets from other intensive field campaigns reaching back five decades; and air quality measurements from the California Air Resources Board monitoring sites, which reach back two to three decades.
The study saw an average drop of 7.5 percent per year over the period of the study. “This is essentially the kind of change we would expect, and it is very good to find that it is actually taking place,” Warneke said. Though, there were a few specific VOCs that did not drop anywhere near as quickly, including propane and ethane, which are chemicals sourced from the use and production of natural gas, and not vehicles.
Warneke said that he would expect 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 of all vehicles on the road.
But this drop in VOCs does not relate very well to an overall drop in ozone levels in the region. According to the researchers, “the air chemistry that leads from VOCs to ozone is more complex than that,” and while ozone pollution has dropped in the Los Angeles Basin area since the 60s, the levels still don’t meet ozone standards set by the EPA.
The improvement in this one measure of air quality in Los Angeles may not surprise many longtime residents, Warneke said. People who lived in the city in the 1960s often couldn’t see nearby mountains through the smog; today, they often can.