NO₂ deposition to elements representative of a forest landscape

Measurements of NO₂ deposition to elements representative of a forest landscape (e.g. foliage, bole, soil) were conducted in an open gas exchange system. Deposition rates (nmol m^-2 s^-1) were calculated as the product of flow rate and the inlet/outlet concentration differential normalized for surface area and corrected for losses to chamber walls. Under daylight conditions and a mean NO₂ concentration of 33 nl ℓ^-1, NO₂ deposition to foliage of forest tree species varied by more than an order of magnitude, ranging from 0.35 (Pinus taeda L.) to 5.75 nmol m^-2 s^-1 (Platanus occidentalis L.), and deposition of NO₂ to most broadleaf species was greater than that to conifers. Sequential light-dark measurements of NO₂ deposition indicated that the principal foliar site of deposition was the leaf interior in support of other observations of stomatal control over NO₂ deposition. Vegetation surfaces typically snowed greater conductance to NO₂ than did distilled water alone, and forest floor samples had a disproportionately high conductance to NO₂ when compared to bark or foliage surfaces. Laboratory data for several forest species were extrapolated to stand-level rates of NO₂ deposition using leaf area index as a scaling factor. Based on appropriate NO₂ concentrations, NO₂ deposition was calculated to provide annual N inputs between 0.08 and 1.9 kg ha^-1 a^-1 of NO₂ derived N(NO₂- N) for natural forests and up to 12kg NO₂-N ha^-1 a^-1 for forest canopies in urban environments.