Capture of particulate pollution by trees:: A comparison of species typical of semi-arid areas (Ficus nitida and Eucalyptus globulus) with European and North American species

Particulate pollution is a serious concern in developed countries especially in urban and suburban areas where it has adverse effects on human health, exacerbating a wide range of respiratory and vascular illnesses. Data are now available which indicate that similar problems probably occur in countries in transition and may indeed be worse where national air quality standards have been neither set nor monitored. Recently a variety of approaches using both wind tunnel and field measurements have suggested that trees can significantly reduce such adverse effects through their ability to capture pollutant particles. It is clear that species choice, planting design and location relative to pollution source are critical in determining the effectiveness of particle capture by trees. Here we present relative deposition velocities and capture efficiencies of five species used widely in woodland of urban and periurban areas of Europe (Quercus petraea (oak), Alnus glutinosa (alder), Fraxinus excelsior ( ash), Acer pseudo-platanus ( sycamore) and Pseudotsuga menziesii ( Douglas fir)), and for two species being used increasingly in semi-arid regions, ( Ficus nitida ( weeping fig) and Eucalyptus. globulus ( Eucalyptus)). These data are for species not previously worked on and measurements were made at three windspeeds. Deposition velocities and capture efficiencies are compared with those published for other tree species, with the values of deposition velocity ranging from 0.1 to 0.3 cm s(-1) at a windspeed of 3 m s(-1) to maximum values 2.9 cm s(-1) at 9 m s(-1) windspeed. Species with more complex stem structure and smaller leaves had greater relative deposition velocities. The use of such data in models to guide species choice and planting design in order to maximise particle removal from urban air are considered.