CARB 1998 - "Measuring Concentrations of Selected Air Pollutants Inside California Vehicles"

California Air Resources Board (CARB)
"Measuring Concentrations of Selected Air Pollutants Inside California Vehicles"
December 1998, Contract No. 95-339, Final Report
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CARB measured concentrations of various air pollutants inside vehicles as a range-finding experiment. They studied the effect of freeway conditions (rush vs. non-rush), roadway types, vehicle types, air vent settings, time of day, and roadside/ambient air quality.

CARB found that pollutant concentrations were higher:

• in the regular vs. carpool lane
• during rush hour
• when following diesel or other high-emitting vehicles

Other findings include:

• Vent settings and vehicle type did not seem to make a big difference
• "Most pollutants levels, especially the VOC's, were elevated inside and outside the vehicles relative to either the roadside or ambient station concentrations"
• "Particle concentrations were typically significantly higher outside the vehicles than inside, presumably due to losses in the vehicle ventilation systems (and other factors) - while significant differences were not observed between inside and outside levels of gas phase pollutants for the same vehicle."

CAVEAT: this was a preliminary, range-finding study, so we should look at other studies for confirmation and hard numbers.