Measurement of Sulfur Dioxide and Ozone Dry Deposition over Short Vegetation in Northern China-a Preliminary Study

At a flat field covered with short grass at the Chinese Research Academy of Environmental Sciences near Beijing, dry deposition of sulfur dioxide and ozone was measured over an approximately 10-d period at the beginning of September and again in the middle of November 2000. The dry-deposition fluxes were estimated on the basis of the gradient method, which is outlined. Wind speed generally started to rise in the early morning, reaching maximum in the mid-afternoon and then decreasing, while temperature followed the normal diurnal and seasonal trends. The mean SO sub(2) concentrations in late summer and early winter were 45 and 97 mu g/m super(3), respectively, and the vertical flux values were -0.11 and -0.32 mu g/m super(2)/s, respectively, while the deposition velocities were 0.2 and 0.4 cm/s, respectively. For O sub(3), the late summer and early winter mean concentrations were 41 and 19 mu g/m super(3), respectively, while the vertical flux values and deposition velocities were -0.10 and -0.08 mu g/m super(2)/s and 0.2 and 0.4 cm/s, respectively. The deposition velocity of SO sub(2) was found to be controlled mainly by the aerodynamic resistance associated with turbulent transfer across the atmospheric boundary layer and by the quasi-laminar boundary-layer resistance, while the deposition velocity of O sub(3) was governed mainly by the surface or canopy resistance.