Surface sample collection and dust source analysis in northwestern China

Analysis of particle size shows that fractions of PM50 (particle <50 μm in diameter) in the alluvial and lacustrine sediments, gobi deserts, shrub dunes, mobile dunes and deteriorated land are 37-99%, 5-7%, 0.26-36%, 0.05-0.4% and 51-62%, respectively. Mobile dunes, which are extensively distributed in northwestern China, are not a significant contributor to geogenic dust emissions due to their very low fractions of PM50. Particle size distributions of different surface types, SEM, X-ray diffractogram and element content analysis all show that lacustrine sediment, shrub dune, gobi desert and deteriorated land are the most potential geogenic dust contributors. These analyses were also applied to the dust samples. Results and monthly dust disposition and dust event distributions show that the dust in the urban region of northwestern China, to a large extent, comes from non-geogenic contributors such as motor vehicle exhaust, coal burning and industrial emission.