The distribution of particulates on leaves was analysed using fourplant species commonly used in living walls with differentmorphology (Fig 2) to develop and validate a sampling protocol.

Figure 2: starting from left Hedera helix, Geranium macrorrhizum, Heuchera, Acorus gramineus

Variation of amount of PM10 along the horizontal and verticaltransects (Fig 3) of leaves was analysed.

Figure 4: Distribution of PM10 along the leaf-transects (each leaf is represented by a different colour)

As shown in Fig 4 particulate distributions on the leaf-blade resultedin lower levels of variation for all four species compared to other leafareas and the leaf-blade was thus selected as the best area tosample leaf sections throughout the study.

Particulate pollution capture by plants on living walls: the impact of rainfall Udeshika Weerakkody, Professor John Dover, Dr Paul Mitchell, The Green Wall Centre, Staffordshire University, UK

Particulate Matter (PM10, PM2.5 and PM0.1) comprises a considerablefraction of urban air pollution, is directly associated with severehealth effects (Laden et al., 2006), and much of it is generated bytraffic (Anon., 2011). Air quality in many large cities in England andWales does not comply with the European air quality standards(Pugh et al., 2012). Vegetation is known to capture particulates andurban greening is a potential method of removing them (Dover,2015). However, the value of living wall systems (Fig 1) in thereduction of traffic-generated particulate air pollution has receivedscant attention (Cheetham et al., 2012).

Figure 1: Left) Leamouth Peninsula Building London (http://nesli1hanaksoy.weebly.com/london-field-tri-building.studies.html), right) Victoria-London

The optimal species composition for particulate capture, fate of thecaptured particulates under different weather conditions and the bestplanting designs for living walls to act as Particulate Matter (PM)traps are not yet understood. This study will employ anexperimentally manipulated living wall system and existing living wallsystems to explore the impact of living wall systems on the reductionof traffic-generated particulate pollution.

Rationale

The inter-species variation of particulate capture PM10, PM2.5 and PM0.1 captured on leaves of twenty plant species

representing different morphological types will be quantified andsize-ranged using an ESEM (Environmental Scanning ElectronMicroscope) and image analysis software (imageJ). Someexample micrographs of particulates captured on leaves are givenin Fig 5. Inter-species variation in particulate capture will beevaluated using GLM (General Linear Model). The elementalcomposition of captured particulates will be determined using theEnergy Dispersive X-ray analysis unit of the ESEM.

Figure 5: SEM micrograph of PM captured on leaves of Heuchera sp. and Hedera helix

The variation in capture levels with different plant combinations,different planting designs, and micro-topographical variations willbe evaluated and the optimisation of species composition forparticulate capture by living walls explored.

Particulate remobilisation due to rainfall is currently being studiedby simulating rainfall using an environmental chamber equippedwith spray nozzles. Leaves were sampled from the roadside, cutin two down the mid-rib, and one half exposed to rainfall.Particulates on both halves of the leaf were then quantified usingthe ESEM and differences in pollution density compared usingpaired t-test (n=20). The procedure was repeated for differentrainfall durations.

Figure 6: Percentage reduction of particulates captured on Hedera helix under differentrainfall durations.

A significant reduction of particulates was observed (Fig 6) onleaves of Hedera helix at all exposure times (p<0.05). Particulatewash-off from the underside of leaves was significantly less(p<0.05) than that from the upper-side of leaves in all sizefractions. A significant proportion of captured particulates iswashed-off by rain, therefore leaf surfaces become available tocapture more particulates. A total of five plant species will bestudied to draw more accurate conclusions on the impact ofrainfall on particulate remobilisation.

Validation of sampling protocol

Distribution of PM10 along the horizontal transect of Geranium leaves

Distribution of PM10 along the vertical transect of Acorus leaves

Particulate remobilisation by rainfall

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• Anon. (2011). City of London Air Quality Strategy 2011-2015. London: DEFRA• Cheetham, N., Woods, A. & Chesterton, V. (2012). Delivering Vertical Greening. Tf L Surface

Transport.• Dover, J.W (2015). Green infrastructure-Incorporating plants and enhancing biodiversity in buildings

and urban environments. Routledge, Abingdon. 120-282.• Laden, F., Schwartz, J., Speizer, F.E. & Dockery, D.W. (2006). Reduction in fine particulate air

pollution and mortality: Extended follow-up of the Harvard Six Cities study. Am. J. of Resp. Crit. Care Medicine.173: 667–72.

• Pugh, T.A.M., Mackenzie, A.R., Whyatt, J.D. & Hewitt, C.N. (2012). Effectiveness of Green Infrastructure for Improvement of Air Quality in Urban Street Canyons. Envir SciTech Lib. 46:7692-7699

References

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