Deposition velocity of O3 and SO2 in the dry and wet season above a tropical forest in northern Thailand

in order to investigate ozone (O-3) and sulfur dioxide (SO2) dry deposition above a forest in a tropical savanna climate in Southeast Asia, field experiments were performed in a teak deciduous forest in Mea Moh, Lampang Province, located in northern Thailand. O-3 and SO2 fluxes were observed on the basis of the aerodynamic gradient method. The experimental period from January to August in 2004 covered the dry (Jan-Apr) and wet (May-Aug) seasons. Both gas concentrations increased in the dry season and decreased in the wet season. Interval estimation of average with a confidence interval of 95% on the deposition velocity data between 25 and 75 percentiles was performed. The intervals of average 03 deposition velocity were estimated to be 0.37-0.39cms(-1) (daytime) and 0.12-0.13cms(-1) (nighttime) in the dry season; and 0.62-0.65cms(-1) (daytime) and 0.25-0.27cms(-1) (nighttime) in the wet season. The intervals of average SO2 deposition velocity were estimated to be 0.10-0.31cms(-1) (daytime) and 0.08-0.31 cms(-1) (nighttime) in the dry season; and 0.95-1.39 cut s(-1) (daytime) and 0.26-0.42 cm s(-1) (nighttime) in the wet season. SO2 deposition velocity in the rain period was significantly higher than that in the no-rain period. Higher deposition velocities in the wet season were mainly caused by non-stomatal uptake of wet canopy due to a lot of wet days, especially in the case Of S02- Much higher daytime deposition velocities in the wet season were additionally caused by stomatal uptake of leafy trees. The applicability of Wesely's parameterization of deposition velocity to a tropical savanna climate was examined. In both gases, the input resistance of transitional spring to the dry season and that of midsummer to the wet season could be applied as a first approximation, although strictly the parameterization Of O-3 non-stomatal resistance needs modification in the dry-season daytime. The applicability of some other parameterizations was also considered. Including the enhanced effect of wet canopy uptake in the non-stomatal resistance was essential in parameterizing SO2 deposition velocity in the wet season of the region. (c) 2006 Elsevier Ltd. All rights reserved.