ABSTRACT
This chapter explores the mechanisms by which trees have the potential to provide two regulating ecosystem services: improved air quality and reduced temperature. It also explores some of characteristics of trees and their planting location that are associated with the greatest benefits. Trees affect the air quality in cities in three ways. First, they can have an aerodynamic effect, whereby their physical presence alters the airflow and turbulence, which in turn affects the dispersion of pollutants. Second, the deposition effect, whereby trees can intercept pollutants and either absorb or capture them on their leaf and woody surfaces. Finally, they can emit pollutants, either directly in the case of volatile organic compounds (VOCs) or indirectly from tree maintenance activities. Trees and other vegetation also require management which may result in an indirect impact on air quality. Cities are warmer than the surrounding rural environment.
