Emission of Particulate Matter (PM10, PM2.5, and PM0.1) comprises a considerable fraction of urban air pollution (Laden et al. 2006, Shackleton et al, 2013). Long term exposure of airborne particulates matter is directly associated with post neonatal infant mortality (Laden et al. 2006), Sudden Infant Death Syndrome (SIDS) (Tracey et al. 2006) and various disease conditions such as; cardiopulmonary, lung cancer (Pope III, 2002), atherosclerosis (Araujo, 2011) and asthma (Anderson et al., 2013). Ultrafine particles (PM0.1) can also change the alveolar macrophage functions with their toxic chemicals (Riddle, 2009). They can go into liver, spleen, kidney, and shockingly to the brain via olfactory nerves (Solomon et al., 2012 cited in Dover, 2015). Entering human blood stream ultrafine particulates can create systemic inflammatory changes which leads to complications in blood coagulability (Seaton et al. 1995). Trees are known to act as a sink for particulates matter. Therefore urban greening is a potential method of reducing traffic-generated particulates in atmosphere. However, there are several limitations; prevailing soil conditions, space utilization, availability of sunlight and size of the trees compare to the buildings in achieving urban greening by purely trees (Johnston et al. 2004). Urban green walls could overcome most of those limitations while providing other benefits including thermal insulation, noise reduction and conservation of urban biodiversity (Alexandri et al. 2007, Dover, 2015). Living walls are vertically growing hydroponic green wall systems which facilitate a variety of plant species with a greater artistic expression (Dover, 2015). It is an emerging global green technology particularly used in the UK, France, USA, Canada, Japan, Singapore (Loh, 2008). Previous studies have focused on the value of climbing plants in the capture of PM and little information is available on the value of living walls in this respect (Cheetham et al. 2012).Therefore the present study aims to look at the role of living wall systems in particulates trapping. Considerable interspecific variation and site specific variation were observed in trapping particulates by vegetation (Beckett et al., 2000b; Freer-Smith et al., 2005, Terzaghi et al, 2013,) and choice of species, designing and sites need to be considered in planning (Beckett et al, 1998 cited in Wang, 2006). Leaf morphological features including surface roughness, leaf hair, length of trichomes, stomata frequency, surface area and epicuticular wax have a considerable impact in particulates trapping efficiency by vegetation (Ram et al., 2012; Dover….., Terzaghi et al, 2013; Shackleton et al, 2013; Pugh, 2012). According to Johnston et al. (2004) combining different floral species including deciduous, herbaceous, annual, perennial, evergreen, foliage, and flowering would capture more particulates. Therefore, this study will be looking at the appropriate species combinations and suitable leaf surface characters for capturing particulates to harness the maximum benefits out of living wall systems. In the UK, traffic-generated pollution has become the major source of particulate matter in air (City of London Air Quality Strategy, 2011-2015) and areas with higher traffic density reported with high PM emission values like 10 µm S-1 (Bruse et al 1999).
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The emission levels are predicted to be increased after 2015 (DEFRA, 2007b) and exposure levels are higher for people within 100 m distance from the road (Zhu et al.,2002b). Therefore, the UK has given more attention towards the areas with high amount of traffic reported in urban greening (City of London Air Quality Strategy 2011-2015). Based on that, locations exposed to more traffic-generated pollution will be selected as experimental sites. Particulates can be trapped on leaves by a variety of mechanisms including impaction when wind passes over the leaf surfaces; capture efficiency may be affected by the surface characteristics (e.g. waxes, hairs) (Pugh 2012, Beckett et al., 2000a, Bidwell and Fraser 1972). Some of the PM can be taken into the plants while others adhere to the surface. However, this trapping could be temporary since there is a possibility of wash-off by rain or re-suspension to the air by wind (Currie et al. 2008, Mc Pherson et al. 1994, Terzaghi et al, 2013).Therefore it is worth exploring the retention of particulates on leaves under different seasonal and weather conditions before selecting the species for living walls. Wang et al (2006) indicated that leaves located closer to
The emission levels are predicted to be increased after 2015 (DEFRA, 2007b) and exposure levels are higher for people within 100 m distance from the road (Zhu et al.,2002b). Therefore, the UK has given more attention towards the areas with high amount of traffic reported in urban greening (City of London Air Quality Strategy 2011-2015). Based on that, locations exposed to more traffic-generated pollution will be selected as experimental sites. Particulates can be trapped on leaves by a variety of mechanisms including impaction when wind passes over the leaf surfaces; capture efficiency may be affected by the surface characteristics (e.g. waxes, hairs) (Pugh 2012, Beckett et al., 2000a, Bidwell and Fraser 1972). Some of the PM can be taken into the plants while others adhere to the surface. However, this trapping could be temporary since there is a possibility of wash-off by rain or re-suspension to the air by wind (Currie et al. 2008, Mc Pherson et al. 1994, Terzaghi et al, 2013).Therefore it is worth exploring the retention of particulates on leaves under different seasonal and weather conditions before selecting the species for living walls. Wang et al (2006) indicated that leaves located closer to