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

Ghasemian, Masoud; Amini, Seyedmorteza; Princevac, Marko

doi:10.1016/j.atmosenv.2017.09.028

Cited by 48 publications

(30 citation statements)

References 55 publications

(61 reference statements)

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“…within and beyond the barrier) 34,53 . Conversely, very low-porosity vegetation can limit pollution removal by restricting infiltration and forcing air pollutants to flow above and around the barrier or to recirculate and accumulate on the upwind or source side 29,54 . An optimal porosity may therefore be inferred to exist between both extremes.…”

Section: Local Scalementioning

confidence: 99%

Section: Density and Porositymentioning

confidence: 99%

“…A higher vegetation barrier density generally results in lower downwind concentrations of both PM 86,98,99 and gaseous pollutants 54,100 . However, CFD modelling undertaken by Ghasemian et al 54 found that a LAD of 3.33 m 2 /m 3 reduced downwind concentrations of roadway emissions (represented by a tracer gas) by 10%, whereas a LAD of 1 m 2 /m 3 increased downwind concentrations by 15%. These findings highlight that due to fluent penetration by pollutants and the introduction of the windbreak effect, very low-density (or very porous) vegetation barriers increase downwind pollutant concentrations until a critical point is reached at which further increases in LAD reduce downwind pollutant concentrations 54 .…”

Section: Density and Porositymentioning

confidence: 99%

“…However, CFD modelling undertaken by Ghasemian et al 54 found that a LAD of 3.33 m 2 /m 3 reduced downwind concentrations of roadway emissions (represented by a tracer gas) by 10%, whereas a LAD of 1 m 2 /m 3 increased downwind concentrations by 15%. These findings highlight that due to fluent penetration by pollutants and the introduction of the windbreak effect, very low-density (or very porous) vegetation barriers increase downwind pollutant concentrations until a critical point is reached at which further increases in LAD reduce downwind pollutant concentrations 54 . On the other hand, at very high densities (or low porosities), vegetation barriers can act as an impermeable obstacle, directing air above and around the barrier and restricting opportunities for pollutant deposition 29,34 .…”

Section: Density and Porositymentioning

confidence: 99%

“…Barrier height, which should generally increase with distance from the road 20 , may be determined according to plant species choice or by planning requirements; barrier width is limited to available planting space; and optimal density can vary somewhat with barrier width 34 . In respect of the non-linear relationship between downwind pollutant concentrations and increasing LAD 54,97 , as well as the importance of semi-permeability 101 , optimal barrier density may be broadly described as above average density but below absolute. Given that the LAD of most naturally occurring vegetation is 1-5 m 2 /m 3 102 , and in line with findings by Ghasemian et al 54 , a LAD of~4 m 2 /m 3 may be recommended.…”

Section: Density and Porositymentioning

confidence: 99%

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Designing vegetation barriers for urban air pollution abatement: a practical review for appropriate plant species selection

2020

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Vegetation can form a barrier between traffic emissions and adjacent areas, but the optimal configuration and plant composition of such green infrastructure (GI) are currently unclear. We examined the literature on aspects of GI that influence ambient air quality, with a particular focus on vegetation barriers in open-road environments. Findings were critically evaluated in order to identify principles for effective barrier design, and recommendations regarding plant selection were established with reference to relevant spatial scales. As an initial investigation into viable species for UK urban GI, we compiled data on 12 influential traits for 61 tree species, and created a supplementary plant selection framework. We found that if the scale of the intervention, the context and conditions of the site and the target air pollutant type are appreciated, the selection of plants that exhibit certain biophysical traits can enhance air pollution mitigation. For super-micrometre particles, advantageous leaf micromorphological traits include the presence of trichomes and ridges or grooves. Stomatal characteristics are more significant for sub-micrometre particle and gaseous pollutant uptake, although we found a comparative dearth of studies into such pollutants. Generally advantageous macromorphological traits include small leaf size and high leaf complexity, but optimal vegetation height, form and density depend on planting configuration with respect to the immediate physical environment. Biogenic volatile organic compound and pollen emissions can be minimised by appropriate species selection, although their significance varies with scale and context. While this review assembled evidence-based recommendations for practitioners, several important areas for future research were identified.

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