[1] A size-segregated aerosol model that includes most of the major physical processes (generation, transport, and dry and wet deposition) is developed. This model is coupled with a Regional Air Quality Model (RAQM) and is applied to simulate Asian dust storms during the 10-day period of 15-24 March 2002. A nonhydrostatic mesoscale model (MM5) is used to provide meteorological fields. Model results are verified by available observational data including surface weather observations and size-segregated particle concentrations. The validation demonstrates a good capability of this model system in capturing most of the key features of dust evolution and reproducing the particle mass size distribution along the transport pathway of soil dust. An apparent feature has been both observed and reproduced by the model, showing a shift of size range with peak mass concentration from coarse mode to finer mode on the pathway from source regions to distant downwind areas. The maximum dust concentration averaged over 10 days is simulated to be 3000 mg m À3 over the southern China-Mongolia border. Total dry deposition of soil dust for 10 days is up to 30 g m À2 in the Gobi desert along the southern China-Mongolia border. Distribution and magnitude of particle deposition are strongly dependent on both concentration and size-segregated dry deposition velocity and scavenging rate. While dry deposition dominates the removal of dust particles in or in the vicinity of source regions, the influence of wet deposition increases along the transport pathway of soil dust, with high removal efficiency for coarser particles (>2 mm) and very low efficiency for particles in the accumulation mode. Of the total dust emission (43.2 megatons), about 71% is redeposited onto the underlying surface by the dry deposition process, 6% is removed by the wet deposition process, and the remaining 23% is suspended in the atmosphere or subject to long-range transport.

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Water-soluble organic nitrogen (WSON) affects the formation, chemical transformations, hygroscopicity, and acidity of organic aerosols as well as biogeochemical cycles of nitrogen. However, large uncertainties exist in the origins and formation processes of WSON. Submicrometer aerosol particles were collected at a suburban forest site in Tokyo in summer 2015 to investigate the relative impacts of anthropogenic and biogenic sources on WSON formations and their linkages with aerosol liquid water (ALW). The concentrations of WSON (ave. 225 ± 100 ngN m–3) and ALW exhibited peaks during nighttime, which showed a significant positive correlation, suggesting that ALW significantly contributed to WSON formation. Further, the thermodynamic predictions by ISORROPIA-II suggest that ALW was primarily driven by anthropogenic sulfate. Our analysis, including positive matrix factorization, suggests that aqueous-phase reactions of ammonium and reactive nitrogen with biogenic volatile organic compounds (VOCs) play a key role in WSON formation in submicrometer particles, which is particularly significant in nighttime, at the suburban forest site. The formation of WSON associated with biogenic VOCs and ALW was partly supported by the molecular characterization of WSON. The overall result suggests that ALW is an important driver for the formation of aerosol WSON through a combination of anthropogenic and biogenic sources.