Sound wall barriers: Near roadway dispersion under neutrally stratified boundary layer

Abstract

a b s t r a c tWith the passage of California Senate Bill 375, which motivates infill development near transit hubs, there is the potential to increase vehicle congestion in residential communities and increase in human exposure to toxic mobile source pollutants. Among all the mitigation strategies that protect near roadway residents from health-affecting vehicular emissions (e.g. separating sensitive receptors from high traffic roadways), this paper discusses the impact of sound wall barriers (SBs) in reducing the air pollution exposure of nearby residents. To date, there have been some studies done to understand the impact of these structures on dispersion of vehicular emissions; however, no definitive conclusion has been drawn yet. The main objective of this paper is to provide more information and details on flow and dispersion affected by barriers through a systematic laboratory simulation of plume dispersion using a water channel. Three sets of experiments were conducted: (1) plume visualizations, (2) plume concentration measurements, and (3) flow velocity measurements. Results from this study shows that the deployment of sound barriers induces a recirculating flow over the roadway which transports the surface released emissions to the upwind side of the roadway, and then shifts the plume upward through an induced updraft motion. Plume visualizations clearly demonstrate that the presence of SBs induce significant vertical mixing and updraft motion on the roadway which increases the initial plume dilution and plume height and consequently results in reduced downwind ground level concentrations. Although different SB configurations result in different localized flow patterns, the dispersion pattern does not change significantly after several SB heights downwind of the roadway.Ó 2015 Elsevier Ltd. All rights reserved. IntroductionNumerous epidemiological studies have shown that long-term exposure to outdoor air pollution increases the risk of respiratory diseases, birth defects, premature mortality, cardiovascular disease, and cancer (Dockery and Pope, 1994;Harrison et al., 1999;Wilhelm and Ritz, 2003;Peters et al., 2004;Jerrett et al., 2005;McConnell et al., 2006). Houston et al. (2006) showed that more than 24,000 childcare centers in California are within 200 m of highly trafficked roadways with more than 50,000 vehicles per day. A statistical analysis has shown that children diagnosed with asthma are more likely to live within 500 m of major roadways (Edwards et al., 1994).

Effects of a Fence on Pollutant Dispersion in a Boundary Layer Exposed to a Rural-to-Urban Transition

“…More recent investigations have focused on the air pollution behind a sound barrier (Baldauf et al. 2008 ; Brechler and Fuka 2014 ; Pournazeri and Princevac 2015 ), although there is a consensus that the problem needs further investigation.…”

The influence of roadside solid and vegetation barriers on near-road air quality

“…Several studies have evaluated the influence of solid barriers on near-road air quality (Amini et al, 2016;Baldauf et al, 2016;Hagler et al, 2011;Pournazeri and Princevac, 2015;Schulte et al, 2014;Steffens et al, 2014Steffens et al, , 2013. Solid barriers induce a significant vertical mixing and shift the plume upward through an induced updraft motion.…”

A sound investment? Traffic noise mitigation and property values

“…Apart from lower noise levels, these amenities include improved energy efficiency due to additional window glazing. In addition, instalment of noise barriers can decrease ambient air pollution from road traffic (Baldauf et al 2008;Pournazeri and Princevac 2015), reduce visual pollution by blocking residents' view of the road (Bangjun, Lili, and Guoqing 2003) and improve traffic safety by separating pedestrians from road traffic.…”