A comparison of observed and parameterized SO_2 dry deposition over a grassy clearing in Duke Forest

摘要

Deposition of trace gases, such as sulfur dioxide (SO_2), 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 SO_2 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 ug m~(-2) s~(-1). Dew on the canopy enhanced the uptake of SO_2, which increased deposition rates. Deposition velocities (Vd) 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.