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

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 (NOx = 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 NOx 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.