The studies, which were collected in the journal Science (pay wall) in January, were conducted over 10 years by team of researchers at Columbia, the University of Southern California, and the University of California, San Diego. The biggest impact of air pollution was measured in farm workers in California's Central Valley, who were paid by the volume of grapes and blueberries they collected. On days that had higher readings of ground-level ozone -- a harmful gas formed when tailpipe emissions mix with sunlight -- worker productivity slumped.
Over the two years they measured the ozone, readings ranged from 10 to 86 parts per billion, and averaged 48 ppb. For every 10 ppb increase in ozone, worker productivity fell 5.5%. For farm workers paid about $9 or $10 an hour, the lost productivity translates into about 45 cents an hour of lower pay, said Matthew Neidell, an economist at Columbia and an author of the studies.