A three-dimensional modeling investigation of the evolution processes of dust and sea-salt particles in east Asia

The evolution of sea-salt and dust particles in East Asia is investigated u sing a three-dimensional transport and chemistry model. A kinetic approach under thermodynamic constraint is utilized to model the condensation/evapor ation processes, and other important aerosol processes and influential comp onents (e.g., dust/sea-salt generation, NH3 emissions, gravitational settli ng, nucleation) are taken into account in this analysis. The model is used to study the Pacific Exploratory Mission-West B period (March 1-6, 1994). I t is found that (1) during strong continental outflow, in general, the fine aerosol mode (< 2 mum in aerodynamic diameter) accommodates sulfate and am monium and the cation-rich coarse mode (> 2 mum in aerodynamic diameter) at tracts nitrate. However, in the dust plume, sulfate preferentially resides in the coarse mode due to larger coarse mode mass loading; (2) particulate nitrate coupled with particulate ammonium in the fine mode is predicted ove r regions where high gaseous NH3 mixing ratios are present (lower courses o f the Huang river); (3) dust and sea-salt particles provide important react ion surfaces for sulfate production in the troposphere and increase sulfate production rates by 20 - 80%; and (4) soil dust and sea salt provide an im portant source of boundary layer and free troposphere alkaline material, an d these cations play an important role in controlling the partitioning of s emivolatile HNO3 throughout large portions of the troposphere, increasing p articulate nitrate levels 10 - 50%.