Commuters Inhale Heavy Dose of Pollution

Driving is more hazardous than anyone knew: A heavy commuter inhales more pollution while driving than in the entire rest of the day, a new study finds.

The research was done in Los Angeles, where the average driver spends 1.5 hours behind the wheel. That time in traffic accounts for 33 to 45 percent of total exposure to diesel and ultrafine particles (UFP), the study showed.

On freeways, diesel-fueled trucks are the source of the highest concentrations of harmful pollutants.

"If you have otherwise healthy habits and don't smoke, driving to work is probably the most unhealthy part of your day," said Scott Fruin, assistant professor of environmental health at the Keck School of Medicine of University of Southern California. "Urban dwellers with long commutes are probably getting most of their UFP exposure while driving."

Ultrafine particles are of particular concern because, unlike larger particles, they can penetrate cell walls and disperse throughout the body, Fruin said. Particulate matter has been linked to cardiovascular disease, but the ultrafine fraction on roadways appears to be more toxic than larger sizes.

Previous research found children on school buses breathe more pollution. And a study in London found people in taxis, buses, and cars all inhale substantially more pollution than cyclists and pedestrians.

In the new study, researchers measured exposure by outfitting an electric vehicle with air pollution instruments. A video recorded surrounding traffic and driving conditions on freeways and arterial roads throughout the Los Angeles region. Measurements were collected during a three-month period from February to April 2003, and four typical days were selected for a second-by-second video and statistical analysis.

"This study was the first to look at the effect of driving and traffic conditions at this level of detail and to demonstrate the specific factors leading to the highest pollutant exposures for drivers," Fruin says. "The extent that a specific type of vehicle—diesel trucks—dominated the highest concentration conditions on freeways was unexpected."

Driving with the windows closed and using recirculating air settings can modestly reduce the particle pollution exposures but does not reduce most gaseous pollutants, the researchers concluded.

"Shortening your commute and spending less time in the car will significantly reduce your total body burden of harmful pollutants," Fruin said.

The study was supported by the California Air Resources Board.

• What is Smog?
• Quiz: What's Your Environmental Footprint?
• The Science of Traffic Jams