Atmospheric trace elements over source regions for Chinese dust: concentrations, sources and atmospheric deposition on the Loess plateau

The mass-particle size distributions of up to 17 trace elements in aerosol particle samples from dust storm and non-dust storm periods were determined for three sites in or near the source regions of Chinese dust. The mass of particulate material in the atmosphere at the sites is dominated by mineral aerosol particles. An absolute principal component analysis of the non-dust storm elemental data for the loess region allows the estimation of the mass contributions from two coarse-particle classes (soil dust and dust associated with pollutants), and two fine-particle classes (soil dust and anomalously enriched). For most elements (Al, Si, Ca, Fe, Ti, K, S and As), the mass-particle size distributions (MSDs) were approximately log-normal. The mass-median diameters (MMDs) of the soil-derived elements tended to decrease with distance from the desert region and when the dust storms subsided. Total dry deposition velocities were calculated by fitting a log-normal distribution to the aerosol data and calculating deposition rates for 100 particle-size intervals using a two-layer deposition model. The mean dry-deposition rates and fluxes were highest during dust storms over desert regions. In thloess region, the calculated dry deposition velocities of soil derived elements (Al, Si, Ca, Fe and Ti) during non-dust storm periods were from 3.1 to 3.7 cm s^-1. From the estimated mass-particles size distributions, the coarser and finer mineral particles were found to benriched with Ca, Fe, Ti and K relative to Al or Si. On a yearly basis, the dry atmospheric input to the Loess Plateau was mainly attributable to normal transport processes, i.e. non-dust storm conditions. Wet deposition fluxes estimated from scavenging ratios indicate that dry deposition dominated the total atmospheric deposition of mineral aerosol. The deposition of aerosol particles associated with coal burning or other anthropogenic sources also was considerable on the Loess Plateau.