"That small difference becomes tremendously magnified when you consider the billions of miles travelled by automobiles every day in this country," said Timothy Buckley, senior author of the study and an associate professor of environmental health sciences at Ohio State University.
"There are easily tens of millions of light trucks on the roads every day" he said.
The researchers conducted their study in an eight-story parking garage in downtown Baltimore. The garage has parking for 1,400 autos and is used by employees and visitors coming to a local hospital and university.
The vehicles were put into one of two categories - light trucks, which included SUVs and minivans, and cars, which included station wagons. A video camera set up at the garage entrance recorded the autos as they entered the facility.
The air within the garage was monitored eight hours a day, from 7 a.m. until 3 p.m., for 24 consecutive days. After the monitoring period got over, the scientists watched the videotape, counting and classifying each vehicle as either a car or a light truck.
They separated the vehicle counts into 30-minute blocks of time. Each 30-minute segment of videotape was matched with the same 30-minute segment of pollution data.
Analysis of three kinds of pollutants emitted from nearly all gasoline-powered vehicles: carbon monoxide (CO), particle-bound polycyclic aromatic hydrocarbons (pPAH) and several volatile organic compounds (VOCs), revealed that the emission of key pollutants from light trucks - a category that includes SUVs and minivans - was 0.5 to 0.6 percent greater than the pollutant levels released by cars.
Prof. Buckley said although the researchers expected to see a bigger impact from light trucks, the seemingly tiny difference between a car and an SUV shouldn't be discounted, as light trucks accounted for about one out of every three vehicles using the garage.
"Our goal was to give some perspective to the concentrations recorded in the garage, and we wanted some basis of comparison," Buckley said. "We were pleasantly surprised to see that the garage concentrations were in fact lower than what was measured at a nearby outdoor site," said Prof. Buckley.
"These pollutants include known and suspected carcinogens. Pedestrian exposure to high levels of these air toxics within parking garages is of concern because of the proximity and intensity of the vehicle activity within the semi-closed environment," he said.
The findings are scheduled for publication in the journal Environmental Research.