Field investigations for evaluating green infrastructure effects on air quality in open-road conditions

Abstract

Many people live, work and spend time during their commute in near-road environments (<50 m) where pollutant concentrations usually remain high. We investigated the influence of roadside green infrastructure (GI) on concentrations of particulate matter ≤10 µm (PM10), ≤2.5 µm (PM2.5), ≤1 µm (PM1), black carbon (BC) and particle number concentrations (PNC) under three GI configurations-(i) hedges only, (ii) trees only, and (iii) a mix of trees and *

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

“…Tong et al 55 found that wide vegetation barriers with a high LAD, as well as vegetation-solid barrier combinations, significantly reduced downwind particle concentrations. However, results from these studies 32,55 suggest variation in concentration reduction efficiencies between particle sizes, which substantiates the conclusion by Steffens et al 97 that although reductions generally increase with the LAD of a barrier, the responses are non-linear. Similarly, based upon results from various studies, Abhijith et al 20 found that an optimal shelterbelt porosity may lie within the range of 20-40% for TSP and 10-20% for PM 10 , implying that optimal porosity is partly determined by target pollutant.…”

“…Further research into the influences of individual plant traits on sub-micrometre PM and individual gaseous pollutant concentrations is highly recommended. However, empirical evidence from field experiments to date supports the generalisation drawn above that dry deposition to GI is influenced by specific traits, or inherited biophysical characteristics, the most significant of which concern leaf surface area and leaf properties or functions 32,36,[88][89][90] . As mentioned, generic recommendations regarding plant selection for pollution (particularly PM) abatement are provided by previous works (e.g.…”

“…proximate to the road) is recommended 7,20,[29][30][31] , particularly for UFP deposition 28 . Vegetation can be utilised to form such a roadside barrier, limiting the exposure of pedestrians to air pollution 8,20,[32][33][34][35] . The optimum physical structure of a vegetation barrier is contextdependent and should take into account the topography of each built environment 7,20 .…”

“…At local scale, the potential for air pollution exposure reduction by appropriate GI is well-supported (Table 1), particularly where GI involves the physical separation of people from pollutant sources, such as by the use of vegetation barriers 42,48 . Indeed, numerous studies have found that vegetation can act as a physical barrier between air pollution and potential sufferers, effectively extending the distance between source and receptor 7,8,20,32,35 , although this function is not without provisos (see 'Trade-offs in plant selection'). Studies on the influences of such vegetation barriers on air quality have largely concerned atmospheric dispersion, and many have compared the dispersion effects of GI with those of grey infrastructure or other non-porous barriers ( Table 1).…”

“…Where vegetation is healthy its density is determined by leaf and branching morphology 41 , which varies greatly between species. A recent field investigation into the influence of GI in open-road conditions on PM 10 , PM 2.5 , PM 1 , BC and particle number concentration (PNC) found that downwind pollutant concentrations generally reduced with an increase in LAD 32 . This inverse correlation is corroborated by results from a CFD modelling study undertaken by Tong et al 55 , which compared the influences of six vegetation and/or solid barrier configurations on near-road particle pollutant concentrations.…”