Measurements of sulfur dioxide and ozone dry deposition over short vegetation in northern China - A preliminary study

We measured dry deposition fluxes Of SO2 and O-3 Over a field covered mostly with short grass in a suburb of Beijing during late summer and early winter. as an initiatory attempt to obtain information on dry deposition in northern China. The measurement was based on a micrometeorological gradient method, and only the data conforming to neutral atmospheric stability were analyzed because the data we collected were not adequate to extend the analysis to other stability cases. The data were further screened out according to a few selection criteria to ensure their credibility. For the selected periods V-d (deposition velocity) of SO2 showed a maximum in the morning and a minimum in the afternoon, with little seasonal dependence in this behavior. The mean ( standard deviation) V-d was 0.2 (+/-0.1) cm s(-1) in late summer and 0.4 (+/-0.2) cm s(-1) in early winter. The diurnal variation of Vd seemed to be more or less governed by that of R-a (aerodynamic resistance) + R-b (quasi-laminar boundary layer resistance), which was considerably larger than R-c (canopy resistance). The mean (+/-standard deviation) V-d Of O-3 was 0.2 (+/-0.2) cm s(-1) in late summer and 0.4 (+/-0.3) cm s(-1) in early winter, thus much the same as those for SO2. The variation Of O-3 Vd was qualitatively similar to that of SO2, but in this case R-c was comparable to or larger than R-a + R-b. Little distinct seasonal dependence was evident for O-3 deposition, either. A tendency was discernible for R-c to increase in the afternoon, which was probably caused by a decline in stomatal conductance due to an increase in vapor pressure deficit and/or a rise in temperature. (C) 2003 Elsevier Science Ltd. All rights reserved.