Influence of Vehicle Design on Near-Road Concentrations of Traffic-Related Air Pollutants

Abstract

Exposure to traffic-related air pollution (TRAP) is an ongoing health concern worldwide, particularly close to roads where concentrations are the highest. Near-road exposure is influenced by factors such as vehicle exhaust emission rates, pollutant composition, and dispersion behavior. In this work we apply a recently developed technique called plume regression based on fast-response roadside measurements, to better understand the variables affecting near-road TRAP concentrations. Of specific interest is determining the extent to which vehicle design and physical characteristics affect roadside exposure to important pollutants such as nitrogen oxides (NO_x = NO + NO₂). We find that the position of passenger car’s exhaust (tailpipe)─whether on the left or right side─results in a 40% difference in pollutant concentration contribution at the curbside. In the UK, only 20.1% of diesel passenger cars, the most significant vehicle class contributors to NO_x emissions, have their exhausts positioned on the right, the position associated with the lowest concentrations. If all diesel cars in the UK were equipped with right-positioned exhausts─the side farthest from the curb, curbside concentrations from these vehicles would be reduced by one-third. We also find evidence that electric vehicles (EVs) act to dilute the exhaust plumes of proximate fossil-fueled vehicles through vehicle-induced turbulence, reducing near-road TRAP exposure, a hitherto unrealized benefit of EVs.

Fast-response measurements of traffic-related pollutants show the physical attributes of a vehicle such as exhaust position influences near-road concentrations.