Los Angeles is still one of the worst cities for all types of pollution, but the air quality is much better than it was in the first State of the Air report released 14 years ago. Days with unhealthy ozone levels have fallen by a third since then, to about 125 days a year.
Improvements in auto engines and clean-burning gasoline have made most of the difference, according to Carsten Warneke, a scientist with the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder.
"The main emissions source [in Los Angeles] is vehicle exhaust, but the cars we're driving are getting better every year," he said.
With those improvements, many of the volatile organic compounds that used to fill the skies of Tinseltown, such as benzene and toluene, have been reduced by about 98%, according to Warneke.
