Modeled size-segregated wet and dry deposition budgets of soil dust aerosol during ACE-Asia 2001: Implications for trans-Pacific transport

[1] Size-segregated budgets of soil dust aerosols in Asia for spring 2001 during ACE-Asia were investigated using the NARCM model [ Gong et al., 2003b]. Simulated mass size distributions of dust deposition showed a similar size distribution to the dust emission fluxes over the source regions and a decreased peak corresponding to a 1 - 3 mum diameter range over downwind regions. The simulations suggest that dry deposition was a dominant dust removal process near the source areas and the removal of dust particles by precipitation was the major process over the trans-Pacific transport pathway, where wet deposition exceeded dry deposition by up to a factor of 10. The Asian dust deposition from the atmosphere to the North Pacific Ocean was correlated not only with precipitation over the North Pacific but also with the dust transport patterns. Variations of monthly Asian dust outflow were identified with the latitudinal center of transport at 38 degreesN in March, 42 degreesN in April, and 47 degreesN in May. The monthly trans-Pacific transport patterns of Asian dust in spring were characterized. The transport axis extended around 30 degreesN and 40 degreesN from the east Asian subcontinent to the North Pacific in March. A zonal transport pathway around 40 degreesN was well developed in April over the North Pacific and reached North America. However, the transport in May was separated into two pathways: an eastward zonal path over the North Pacific and a meridional path from the source regions to the northeast Asian continent. On the basis of the averaged dust budgets during spring 2001, it was found that the major sources of Asian dust were located in the desert regions in China and Mongolia with an estimated dust emission of 21.5 tons km(-2), and the regions from the Loess Plateau to the North Pacific were sinks of soil dust aerosols with the Loess Plateau as the main sink for Asian dust

Characterization of soil dust aerosol in China and its transport and distribution during 2001 ACE-Asia: 2. Model simulation and validation

[1] A size-segregated soil dust emission and transport model, Northern Aerosol Regional Climate Model (NARCM), was used to simulate the production and transport of Asian soil dust during the Aerosol Characterization Experiment-Asia (ACE-Asia) period from March to May 2001. The model is driven by the NCEP reanalyzed meteorology and has all the atmospheric aerosol physical processes of soil dust: production, transport, growth, coagulation, and dry and wet deposition. A Chinese soil texture map that infers the soil grain-size distribution with 12 categories was generated to drive the size-distributed soil dust emission scheme [Alfaro et al., 1997; Marticorena and Bergametti, 1995]. The size distribution of vertical dust flux was derived from the observed surface dust-size distribution in the desert regions. Parameters applicable to the Asian deserts for the dust emission scheme are assessed. Model simulations were compared with ground-based measurements in East Asia and North America and with satellite measurements for the same period of time. The model captured most of the dust mobilization episodes during this period in China and reasonably simulated the concentrations in source regions and downwind areas from East China to western North America. About 252.8 Mt of soil dust below d < 40 mu m was estimated to be emitted in the East Asian deserts between 1 March and 31 May 2001 with similar to 60% attributed to four major dust storms. The vertical dust loadings above 700 hPa correlate reasonably well with Total Ozone Mapping Spectrometer aerosol index ( TOMS AI) observations. The sensitivity analysis of model performance to soil size distribution, water moisture, and meteorology was carried out with the observational data to establish the most appropriate parameters and conditions for the Chinese soil dust production and transport