ABSTRACT
This chapter discusses how urban trees can contribute to mitigation of pollutants in highly urbanised areas. Mitigation using urban forestry could address part of the problem, with one of the most important ecosystem functions of vegetation in densely populated areas and along roads being to help protect people from pollution. The effect of vegetation on air quality depends on how it interferes with deposition and dispersion of pollutants. Vegetation can reduce wind speed, direct air flow and intercept particles and gases, depending on physical attributes such as height and canopy structure, the position in the urban landscape and the distance to pollution sources. The release of biogenic volatile organic compounds (BVOC) from vegetation can have significant air quality implications in polluted urban areas, since they are involved in ozone formation or removal. Since the quality and quantity of BVOC emissions is species-specific, this aspect must be considered when determining the appropriate choice of vegetation for large-scale urban tree planting programmes.
