科研之友
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摘要
An investigation of the influence of mineral dust on trace gas cycles in the troposphere is carried out in this study. A 3D regional scale atmospheric chemistry model (STEM-III) which includes aerosol processes is used for the numerical simulations for May 1987. Heterogeneous interactions between gaseous species (SO2, N2O5, HNO3, HO2 and H2O2) and the dust particles are considered. Emissions of dust behind convective cold fronts are modeled. The transport and distribution of mineral dust predicted from the model is compared with satellite measurements (aerosol index from TOMS). The model is shown to capture the synoptic variability in the observed aerosol index. Calculations show two major dust events in May 1987, during which the dust levels close to the source reach more than 500 mu g/m(3). The transport of dust is mostly restricted towards the north, with the net continental outflow of similar to 6 Tg for the entire month. Results show that the presence of mineral aerosol can greatly impact sulfate and nitrate distributions. Averaged over the month of May, the presence of dust is estimated to increase particulate sulfate and nitrate levels in east Asia by similar to 40%. Furthermore, the sulfate and nitrate on the dust particles are predicted to be associated with the coarse mode (3-5 mu m particle diameter), consistent with observations over Japan. The influence of mineral dust on the photochemical oxidant cycle is also investigated. For the entire month, a 5-10% decrease in boundary layer ozone is predicted by the model closer to regions of higher dust levels. The ratio of nitric acid to NOx over marine regions is reduced by a factor between 1 and 2 in the boundary layer to more than 2 in the free troposphere as a result of aerosol processes.
- 出版日期2000-7
