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 P. H. FREER-SMITH 1 , A. A. EL-KHATIB 2 and GAIL TAYLOR 3∗ Forest Research, Alice Holt Lodge, Wrecclesham, Surrey GU10 4LH, UK; 2 Department of Botany, Faculty of Science, 82524 Sohag, Egypt 3 School of Biological Sciences, Bassett Crescent East, University of Southampton, Southampton, SO16 7PX, UK ( ∗ author for correspondence, e-mail: g.taylor@usoton.ac.uk) (Received 17 March 2003; accepted 16 December 2003) Abstract. 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 meas- urements 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. Keywords: air pollution, capture efficiencies, deposition velocities, particulates (PM 10 ), trees 1. Introduction Particulates in the air are a serious problem in industrial and urban areas of both developed countries and those in transition. For example, Moolgavhar and Hutchin- son (2000) identified a positive correlation between hospital admissions from chronic respiratory diseases and the index of respirable particles in air monitored in Seattle (Washington, U.S.A.). The recent report of the World Health Organisation, which looked at vehicular emissions of particles in three European countries, revealed that more people were killed prematurely by the effects of these pollutants than Water, Air, and Soil Pollution 155: 173–187, 2004. © 2004 Kluwer Academic Publishers. Printed in the Netherlands.