Acid rain model: Canopy module

A canopy model has been developed to calculate throughfall characteristics based on canopy properties, ambient air quality, and precipitation quantity and quality. The processes considered include wet and dry deposition, leaf exudation, nitrification, and oxidation of SO₂ and NO_x. The model has been calibrated with data collected at Woods Lake in the Adirondack Mountains of New York. The model has accurately simulated throughfall volume and the concentration of 15 throughfall chemical constituents. Ammonium (NH⁺₄) accumulated on the canopy is nitrified rapidly, resulting in an increase in acidity and nitrate fluxes. The dominant process occurring in the coniferous canopy is dry deposition. The enrichment of acidity in coniferous throughfall is derived primarily from the accumulation of acidic air particulates. The dominant process occurring in the deciduous canopy is exudation. This partially neutralizes the acidic deposition.