Most pollution studies of freeways in the past were conducted during the day or evening, when weather conditions are more conducive to containing particulate matter from drifting downwind. But a 2009 study of the 10 Freeway through the heart of Los Angeles, conducted before sunrise, found air pollution much farther from the road, according to the Los Angeles Times.
So CARB cranked up its mobile monitoring equipment, Toyota RAV 4 Electric Vehicles, and hit the road with UCLA researchers in 2011 to take samples in neighborhoods surrounding four different freeways in Los Angeles County before dawn.
They found a lot more pollution. The culprits are surface inversions caused by evening cool air that trap concentrated pollutants near the ground, allowing the gunk to blow farther away.
The researchers speculated that the dispersed pollution means that one in four people living in the Los Angeles area might be exposed to hydrocarbons, nitric oxide and other particulate matter that can lead to asthma, heart disease and other ailments.