This NCST graduate fellowship award enabled Faraz Ahangar to finish his project on the effect of sound walls and vegetation barriers on the dispersion of highway pollutants. This project examined the effects of road configurations and urban vegetation on the air quality impact of vehicle-related emissions and used this understanding to suggest methods to mitigate the impact of these emissions on urban air quality. During the NCST award year, Faraz was able to conduct a field study to estimate the incremental effect of tall vegetation on the mitigation caused by a solid barrier. The study was conducted in the vicinity of a highway in Sacramento, California. The road had two 500m stretches, one of which was a solid barrier, and the other has tall trees behind the barrier. This allowed the research team to make simultaneous measurements of vehicle-related species at several locations downwind of these two barrier types. The researchers observed that the addition of vegetation behind the solid barrier reduced turbulence levels in the entire sampling period. Their measurements also showed that vegetation behind a solid barrier could cause a reduction in concentrations in general; however, this was not the case for all of the observed data. The research findings are explained thoroughly in a final report to the California Air Resources Board (CARB). A software was also developed to model the impact of roads with roadside barriers on the surrounding communities.
