AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Effectiveness of Sound Wall-Vegetation Combination Barriers as Near-Roadway Pollutant Mitigation Strategies
DILHARA RANASINGHE, Isis Frausto-Vicencio, Wonsik Choi, Eon Lee, Yifang Zhu, Faraz Enayati Ahangar, Akula Venkatram, Seyedmorteza Amini, Steve Mara, Suzanne Paulson, University of California Los Angeles
Abstract Number: 147 Working Group: Passive Mitigation Strategies to Reduce Exposure to Near-Road Air Pollution
Abstract Evidence of the dangers of roadway pollutant exposure is growing, elevating the need to protect populations from roadway pollution. Many pollutants are elevated around roadways, including black carbon, carbon monoxide, ultrafine particles, NOx, and gasses such as benzene. Vegetation planted in combination with solid barriers along the sides of major roadways can potentially reduce downwind pollutant concentrations. However, to date, studies of the effect of sound/vegetation walls have not yet produced definitive results. Here, we report results from field studies characterizing the effectiveness of sound and vegetative barriers in dispersing and removing pollutants at four sites in California. The sites had a variety of different barrier configurations, including no barrier, a solid soundwall, a soundwall combined with vegetation, and vegetation only. Several traffic-related pollutants including fine particulate matter (PM2.5), ultrafine particles, and oxides of nitrogen, as well as micrometeorology were measured during both nighttime and daytime hours and in different seasons. Stationary monitoring, mobile monitoring, vegetation characterization and detailed data analysis and analytical models are combined analyze pollutant concentrations in the barriers. Traffic volumes, speeds and fleet mix on the roadway, were also considered. The measurement data and model indicate that barriers reduce pollution levels downwind of roadways by a maximum of about 50% compared to no-barrier, although more generally reductions are more modest. Both solid barriers and vegetation barriers were observed to be effective at reducing pollutant levels. As vegetation used in combination with a solid barrier can extend the height of the effective height of a solid barrier, the addition of vegetation to a solid barrier can enhance its effectiveness. However, in the configurations studied here, this enhancement was modest, no more than 25%, and likely closer to 10%. Under conditions with light winds, tall vegetation alone was more effective at reducing pollutant concentrations than a shorter combination of vegetation and solid barrier. In summary, trees planted along roadways confer modest benefits in their ability to reduce pollutant levels downwind.