Atmospheric sulfur deposition for a red soil broadleaf forest in southern China

A two-year study in a typical red soil region of Southern China was conducted to determine 1) the dry deposition velocity (V-d) for SO2 and particulate SO42- above a broadleaf forest, and 2) atmospheric sulfur fluxes so as to estimate the contribution of various fractions in the total. Using a resistance model based on continuous hourly meteorological data, atmospheric dry sulfur deposition in a forest was estimated according to V-d and concentrations of both atmospheric SO2 and particulate SO42-. Meanwhile, wet S deposition was estimated based on rainfall and sulfate concentrations in the rainwater. Results showed that about 99% of the dry sulfur deposition flux in the forest resulted from SO2 dry deposition. In addition, the observed dry S deposition was greater in 2002 than in 2000 because of a higher average concentration of SO2 in 2002 than in 2000 and not because of the average dry deposition velocity which was lower for SO2 in 2002. Also, dry SO2 deposition was the dominant fraction of deposited atmospheric sulfur in forests, contributing over 69% of the total annual sulfur deposition. Thus, dry SO2 deposition should be considered when estimating sulfur balance in forest ecological systems.