Stuck on the Freeway? Here’s Something Else to Fume About
Spending time in traffic -- especially when the conditions are stop-and-go -- could be bad for your health because of the air pollution flowing into your automobile, recent research shows.
Although rolling up the windows might help a bit, no car is airtight. Turning on the fan makes only a modest difference at best, experts say. Short of donning a gas mask or holding your breath, your best bet is to avoid driving behind certain types of diesel vehicles and to minimize your time on congested freeways.
“Since traffic is the major source of toxins, you’re getting substantial exposure to these agents in your daily commute,” said Jean Ospital, health effects officer for the South Coast Air Quality Management District. The health risks, he added, increase with the amount of exposure.
One recent study, funded by the U.S. Environmental Protection Agency, suggests that exposure to air pollution particulate matter while driving could cause cardiovascular changes that have been associated with increased risks of heart attacks, inflammation and arteriosclerosis.
Published in the April 15 issue of the American Journal of Respiratory Critical Care Medicine, the study followed nine North Carolina state highway troopers for four days. The officers -- all nonsmokers between the ages of 23 and 30, and in “excellent physical condition” -- were connected to electrodes that kept track of their heart rate. Blood samples were drawn before and after each work shift. Patrol cars were equipped with devices to monitor air quality.
By having the troopers keep a log of their daily activity, researchers were able to factor out stressful events -- such as a high-speed chase -- that might be responsible for some cardiovascular responses.
Still, they observed that for these healthy men, exposure to particulate matter while inside their vehicles was correlated with irregular heart rhythm, elevated blood protein levels and other blood cell changes.
“The higher the dose of air pollution, the more we saw a [cardiovascular] change,” said study co-author Dr. Wayne E. Cascio, chief of cardiology at Brody School of Medicine at East Carolina University. “A high level [of pollution] for a short term could be the same as a smaller dose over a long period of time.”
In a follow-up study to be published in the journal Particle and Fibre Toxicology, Cascio and his colleagues found that the connection between air pollution and cardiovascular changes seemed particularly strong when it came to stop-and-go traffic, which generates more air toxins than smooth driving. Chemical analyses of the air inside patrol cars found that acceleration increases the level of aldehyde in the air, while braking releases copper metal particles.
A separate study, published in August in the journal Atmospheric Environment, found that driving behind certain types of diesel vehicles can dramatically elevate the levels of black carbon -- or diesel soot -- in the air inside your car.
The study said that being behind a diesel bus with a low tailpipe could subject you to 18 times as much black carbon than if you are tailing a modern, gasoline-powered passenger vehicle.
The amount of black carbon in the air is an indicator of the level of diesel exhaust. According to the AQMD, 90% of the cancer-causing air pollution in the region comes from vehicle emissions, and the major source of cancer-causing toxins is diesel exhaust.
Ironically, the study showed that exposure to black carbons may be higher when you’re behind a medium-size delivery truck with a low tailpipe or a diesel passenger car than when you’re tailing a big rig with exhaust piping out its top. That’s because the smaller vehicles blow toxic particles directly at your car.
“By far, the best thing to do is avoid driving behind these vehicles and avoid driving on freeways dominated by these vehicles,” said Arthur M. Winer, professor of Environmental Health Services at the UCLA School of Public Health and a co-author of the study. “That will help reduce your exposure.”
Winer and his colleagues also found that the time people spend inside their car averaged 1 1/2 hours a day -- or about 6% of their time -- but accounted for one-third to one-half of their daily exposure to diesel exhaust.
The diesel study analyzed data that had been collected in 1997 by researchers funded by the California Air Resources Board. By equipping a car with an air-quality monitor, researchers measured real-time black carbon levels inside a car driving on freeways and roads in Los Angeles and Sacramento. Windows were closed, and different fan settings were used. Each run was recorded by a video camera aimed at capturing what was in front of the driver.
The most important predictor of black carbon levels inside the test vehicle was the type of vehicle followed, the 2004 analysis found. Researchers did not control for whether air conditioning was used, but found that variables such as speed, following distance and ventilation did not matter much.
“Vehicles are very porous,” Winer said. “They’re not space capsules. They’re not submarines. They’re not airtight.”
Some manufacturers of car air purifiers sold in stores and over the Internet claim their products can eliminate toxins and remove odors. But air pollution experts and others are skeptical.
Last year, Consumer Reports tested several in-home air purifiers and deemed them “not effective.” The organization has not reviewed any in-vehicle air purifiers.
“Some of them generate ozone to destroy odors,” professor Roger Atkinson, director of the Air Pollution Research Center at UC Riverside, said of such devices in general. “The thing about ozone is it kills your sense of smell. That’s why you don’t notice odors anymore.”
Atkinson and others say it is ironic that such devices can add ozone, considering that it’s the main ingredient in Southern California’s smog.
“We’ve worked 35 years trying to reduce ozone!” said Jerry Martin, spokesman for the Air Resources Board.