In determining the effect of aerosols on forest trees, it is necessary to estimate the deposition of aerosols to forests. To this end we must consider the arboreal factors that influence the deposition of aerosols on forest trees. This paper examines such relevant factors as canopy shape, shoot structure, and leaf surface structures. Laboratory and field experiments in urban areas show that these factors play an important role in the deposition of aerosols on trees. SEM-EDX analyses have determined the chemical composition of particles deposited on the surfaces of tree leaves in urban areas. In forests, however, details of aerosol particles deposited on leaf surfaces is not known, and the effect of abiotic factors such as rainfall, fog and wind has not been determined. Further information is needed, including experimental data about the aerosols deposited on leaf surfaces of trees in a forest, taking into account canopy shape, leaf surface structures and tree phenology.