Modeling Study On Black Carbon And Soil Dust Aerosols In China

Black carbon (BC) and dust aerosols are the major aerosols impacting on Chinese climate and environment, especially the BC transport and depositions over the Tibetan Plateau (TP) and the springtime dust storms in northern China playing an important role in the climate change. With this purpose, this study includes1) based on the aerosol simulations over10years of1995-2004with a global aerosol climate model system GEM-AQ/EC to characterize the seasonal features of BC aerosol transport and depositions over the Tibetan Plateau (TP) and2) a sensitivity experiment of boundary layer schemes in modeling a dust storm event in Northern China by using the regional climate model RegCM4.1. The analysis results are concluded as follows:The BC-aerosols over the TP are transported in the free troposphere and within the boundary layer. The BC-transport to the TP is more efficient within the boundary layer from the South, East and Southeast Asian source regions near to the TP, contributing to the TP-distributions of BC concentrations and depositions with the increasing gradients from west (north) to east (south). The BC-transport across Eurasian continent in the free troposphere in the unchanged direction from west to east varied from the weak fluxes with the northward pathway in summer to the strong fluxes with the southward pathway in winter.Governed by the Asian monsoon circulations, the BC-transport to the TP within the boundary layer had the more significant seasonality. The BC-transport from South Asia crossing the Bay of Bengal reached the southeast TP in spring and climbing over the Himalayas entered the interior of south TP in summer. The northward expanded summer monsoon flows in China drive the BC-transport from the central China to northwest TP. Accompanied with the withdraw of summer monsoon and development of winter monsoon during autumn and winter in South and East Asia, the BC transport from South Asian source to the TP declined, the east winds at the south and southwest sides of anticyclone in East Asia force BC-transport from southeast China in autumn and from the Southeast Asian sources in winter to the southeast TP. Controlled by the seasonal shift between warm and wet to cold and dry climate over the TP, wet and dry BC-depositions, respectively, dominate the total BC depositions over the TP in summer and winter. Over the large TP-areas, the total BC-depositions in summer exceed8-10kg km-2season-1with the high center of40kg km-2season-1at the northeast part, while the total BC-depositions in winter drop to less than5kg km-2season-1.The total BC-depositions over the TP are found to fluctuate seasonally with a factor of2-8between the maximum in summer the minimum in winter.Two options of boundary layer schemes in the model RegCM4.1:Frictionless and Holtslag PBL were tested respectively in March2002of a sand-dust storm simulation. The frictionless scheme with adiabatic and kinetic energy dissipation-free in the boundary layer could result in a unrealistically larger wind speed on the ground. Because the dust emissions are exponentially proportional to the friction wind velocity, The modeling experiment with the frictionless scheme provide higher dust emissions in both strength and area compared to the Holtslag PBL simulation. Non-local turbulent flux parameterization of Holtslag PBL reasonably simulates the surface wind speed with vertical diffusion in atmospheric boundary layer, the simulated dust concentrations are consistent with the surface of sand-dust aerosol observations in Northern China, thereby illustrating an important role of boundary layer parameters in dust aerosol modeling study.