Car ventilation settings determine pollution exposure

Your car ventilation settings have a major effect on the levels of exposure to particulate pollution while driving, according to a new study.

Particulate pollution is the black, sooty smoke produced by diesel engines and coal-fired power plants.

In this study, researchers from the University of Southern California (USC) measured in-vehicle particulate pollution exposure in a wide range of car types and operating conditions.

"Short of driving less, putting your ventilation to 'recirculate' is the best way to reduce exposure to all types of vehicle-related particulate pollution," study senior author Scott Fruin, an assistant professor of preventive medicine at USC, said in a university news release.

Double daily exposure

"Otherwise, an hour-long commute to work or school can double your daily exposure to traffic-related particulate air pollutants," he added.

Compared to ventilation settings that bring in outside air, the "recirculate" setting reduced in-vehicle pollution from 80 percent of on-road levels to 20% for small-particle pollution and from 70% to 30% for larger particles, the researchers found.

The windows of the cars were always kept closed for the study. Keeping windows open while driving quickly raises inside pollutant concentrations to the same levels as on-road levels, the researchers said.

They also found that particulate pollution levels are lower in newer cars, at slower speeds and when driving on arterial roads instead of freeways. Pollution levels are five to 10 times higher on highways than in other locations, according to the researchers.

Leaving the windows closed over 30-minute or longer drives with several passengers raised carbon dioxide levels in the cars, Neelakshi Hudda, a research associate in the environmental health department at USC's Keck School of Medicine, said in the news release.

"Some people are sensitive to high [carbon dioxide] concentrations," Hudda said. "To prevent this, outside air should be pulled in every 10 or 15 minutes for a minute or two, especially if there are two or more people in the vehicle."

The study was published online recently in the journal Environmental Science & Technology.

More information

The US Environmental Protection Agency has more about particulate pollution.