15 June 1999

The California Air Resources Board (ARB) and the South Coast Air Quality Management District (SCAQMD) completed a study on exposure to air pollutants inside vehicles. The two-year, $440,000 study was the first ever to gather particulate data inside vehicles and the first to collect real-time information under a range of traffic and driving conditions. It was found that exposure to several air pollutants was higher inside vehicles than in ambient air.

Dr. Alan Lloyd, ARB Chairman, said “We’re learning that peoples’ highest daily exposure to air pollutants may be during their commute to and from work. Also, we have concerns about the potential impact on bus riders, especially children. Therefore, I’ve asked the ARB staff to collect more data to evaluate the risks.”

The study’s objectives were to measure motorists’ personal exposure to common motor vehicle pollutants in Los Angeles and Sacramento, two areas that have high levels of motor vehicle-generated air pollution. Funded by the ARB, with support from the SCAQMD, the study measured the direct exposure to motor vehicle occupants from gaseous pollutants, diesel soot and other fine particles.

As part of the study, ARB researchers also began looking at pollutant levels inside school buses. Future ARB research may include projects that will better define the pollutant levels to which children are exposed while traveling to and from school.

Researchers found levels of hydrocarbons and carbon monoxide were between two and ten times higher inside vehicles than at roadside or fixed monitoring stations. Researchers also found similar levels of toxic compounds such as benzene, 1,3-butadiene, ethyl benzene, toluene, xylene and MTBE, all considered toxic by the ARB and US EPA. The variations depended on the pollutant, the type of road and the level of traffic.

Researchers found that as much as one-half of the pollutants inside test cars were emitted by the vehicle ahead. In general, levels of toxics and other pollutants are higher inside vehicles than in outdoor ambient air because cars are surrounded by emissions from other vehicles on freeways and streets.

Study summary from ARB

Source: California ARB