A comparison of observed and parameterized SO2 dry deposition over a grassy clearing in Duke Forest

Deposition of trace gases, such as sulfur dioxide (SO2), can affect plant and soil chemistry in different ecosystems. Measurements over a complex ecosystem, like a forest clearing, are necessary to determine more accurate deposition rates that can be used to improve parameterizations and models. The flux-gradient technique was used to determine SO2 fluxes over grass in a clearing at Duke Forest, North Carolina, USA on 25 June - 2 July 2008. The mean flux was -0.037 +/- 0.024 mu g m(-2) s(-1). Dew on the canopy enhanced the uptake of SO2, which increased deposition rates. Deposition velocities (V-d) fluctuated greatly with a mean of 1.00 +/- 0.48 cm s(-1). The large variation in V-d was not fully captured by estimates determined from a multilayer model (MLM) and a big-leaf model (BLM). Mean deposition velocities derived from the MLM and BLM were 1.25 +/- 0.21 cm s(-1) and 0.63 +/- 0.12 cm s(-1), respectively. The model estimations of V-d in this study were probably affected by uncertainties associated with canopy resistance, particularly with stomatal and non-stomatal processes. Published by Elsevier Ltd.