Characterization of MASDs of surface soils in north China and its influence on estimating dust emission

The micro-aggregated size distribution (MASD) of surface soil is an important parameter for modelling dust emission. However, there is no dataset of MASDs of all surface soil types in north China. The MASDs are here presented, measured by dry sieving, for typical surface soil samples, including sandy soil, gravelly sand soil, gravelly loam soil, loam soil and silt loam soil, collected from sandy deserts, Gobi deserts, oases, farmlands in steppe regions and steppe areas in north China. The MASDs of various surface soil types exhibit a combination of several log-normal distributions of five separated sizes with mean mass median diameters (MMDs) of 90, 210, 390, 600 and 980 mm, respectively, and mean standard deviations (SDs) of 1.25, 1.40, 1.25, 1.35 and 1.25 respectively. The log-normal distributions correspond to very fine sand, fine sand, medium sand, coarse sand and very coarse sand population. On the basis of characterization of the retrieved MASDs of various surface soil types in north China, dust emission fluxes are modelled by a dust production model (DPM model). It is shown that dust emission has been significantly influenced by MASDs. Fine sand and very fine sand are always associated with the highest dust emission fluxes. Emission fluxes of the medium sand, gravelly sand soil, gravelly loam soil and loam soil are lower than those of very fine sand and fine sand, but larger than those of the coarse sand. The differences in dust emission fluxes vary among the different soil types from 10¹ to 10³ mg·m^-2·s^-1. Dust emission fluxes from sandy deserts and farmlands covered with sand sheets in north China rang from 10¹ to 10⁴ mg·m^-2·s^-1 while those from Gobi deserts, farmlands and steppes with gravelly desertification range from 10¹ to 10² mg·m^-2· s^-1. The modelled results indicate that deserts and farmlands with sand are the major dust sources in north China.