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

Myles, LaToya, Heuer, Mark W., Meyers, Tilden P., Hoyett, Zakiya J.
Atmospheric environment 2012 v.49 pp. 212-218
atmospheric chemistry, canopy, dew, dry deposition, ecosystems, forests, gases, grasses, models, soil chemistry, sulfur dioxide, North Carolina
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 μg m⁻² s⁻¹. Dew on the canopy enhanced the uptake of SO₂, which increased deposition rates. Deposition velocities (Vd) fluctuated greatly with a mean of 1.00 ± 0.48 cm s⁻¹. The large variation in Vd 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 Vd in this study were probably affected by uncertainties associated with canopy resistance, particularly with stomatal and non-stomatal processes.