In Case You Missed It: Traffic-Related Air Pollution

By Lindsay Yee, Assistant Project Scientist, University of California, Berkeley

Along roads heavily utilized by vehicles, traffic-related air pollution (TRAP) remains an ongoing health concern around the world. While there are many variables that can influence the levels of TRAP and exposure to humans, Wilson et al., examine factors in vehicle design (i.e. which side tailpipe position is, aerodynamics) that can influence curbside TRAP. They measured roadside NOx and CO2 as markers of tailpipe emissions and utilized a technique called plume regression to better understand the dynamics of roadside TRAP. 

One main finding is that for tailpipe positions being on the right side of the vehicle (further from the curb in the UK), resultant CO2 coefficients (the increase in roadside CO2 associated by vehicle type) are 36-41% lower than if the tailpipe was located on the left side of the vehicle for diesel, gasoline, and gasoline-hybrid type cars. The study points out that only about 20% of diesel-type vehicles have their tailpipes located on the right side of the vehicle, proposing that near-road concentrations of TRAP (in this case, NOx) could be reduced by a third if all diesel vehicle tailpipes were located on the left side instead. 

Further, a less realized benefit of electric vehicles (EVs) that do not have substantial tailpipe emissions is that their passing leads to added turbulence and dilution of TRAP that would be experienced roadside. The larger (e.g. frontal area) and faster EVs are, the greater this effect becomes. As the authors note, a natural extension and next step for this study is to deploy point sampling with particle number and concentration measurements, apply plume regression, and observe the impacts of vehicle type and design factors on near roadside particulate matter levels.

Read the full text, accepted May 13, 2025 to ACS EST Air:

Wilson, S., Farren, N. J., Bernard, Y., Shaw, M. D., Lee, K., Crowe, M., Lee, J. D. and Carslaw, D. C.: Influence of Vehicle Design on Near-Road Concentrations of Traffic- Related Air Pollutants, ACS EST Air, doi: 10.1021/acsestair.5c00059, 2025.