Environmental health researchers from UCLA, the University of Southern California and the California Air Resources Board have found that during the hours before sunrise, freeway air pollution extends much further than previously thought.
Air pollutants from Interstate 10 in Santa Monica extend as far as 2,500 meters — more than 1.5 miles — downwind, based on recent measurements from a research team headed by Dr. Arthur Winer, a professor of environmental health sciences at the UCLA School of Public Health. This distance is 10 times greater than previously measured daytime pollutant impacts from roadways and has significant exposure implications, since most people are in their homes during the hours before sunrise and outdoor pollutants penetrate into indoor environments.
The study was published last month in the journal Atmospheric Environment, with Dr. Shishan Hu, a postdoctoral scholar at the UCLA School of Public Health, as lead author.
“To measure the pollution levels, we equipped an electric vehicle with no emissions of its own with fast-response instruments for gaseous and particulate air pollutants, a GPS and video monitor, and instruments to measure temperature and winds,” Winer said. “In both winter and summer of 2008, we drove toward and away from Interstate 10 on a route perpendicular to the freeway in Santa Monica between the hours of 4 a.m. and 7 a.m.”
A second striking finding of the study was that although traffic volumes are lower in the pre-sunrise hours, the air pollution concentrations measured by the team were higher than even those during daytime traffic congestion peaks. Concentrations are higher before sunrise even though emissions are lower because of the unique weather conditions.