Smog obscures the L.A. skyline.

Smoggy days like this one -- Nov. 8, 2005 -- are less frequent today in Los Angeles, even though there are many more cars on the road, according to new research. Scientists credit California's strict emissions standards. (Bryan Chan / Los Angeles Times / November 8, 2005)

Despite a three-fold increase in people and cars in the last 50 years, California’s strict vehicle emissions standards have managed to significantly clear the state’s air, according to  new research.

The study also found that Southern California’s air chemistry has changed for the better. The amount of organic nitrates in the atmosphere — which cause smog’s eye-stinging irritation — has drastically fallen off, according to federal researchers.

Ozone and other pollutants have been monitored in the state since the 1960s. Since then the population in Southern California has tripled, as has the number of cars on the road. Nevertheless, tailpipe emissions have decreased.   

The National Oceanic and Atmospheric Administration’s Cooperative Institute for Research in Environmental Sciences at the University of Colorado led the research, which analyzed decades of data and collected air samples from overflights in 2010.

The researchers credited the state’s stringent emissions standards with bringing about the pollution reductions, although they note that automobiles remain the dominant emissions source in Los Angeles.