Variation of sources and mixing mechanism of mineral dust with pollution aerosol - revealed by the two peaks of a super dust storm in Beijing

The observation of the super dust storm in Beijing from 20 to 22 March 2002 with high-time resolution showed that there were two peaks of TSP of 10.9 and 5.1 mg m(-3) with 87% and 60% of the mineral dust to TSP, respectively. The variation of sources and mixing of mineral dust with pollution aerosol was distinguished with hourly meteorological data and lidar observation and identified by horizontal visibility and chemical tracers. The dust in PI mainly originated from source I, which included west and middle regions of northern China and the nearby Gobi desert in Mongolia, and the dust in PII was mostly from source II, which mainly included the northeast of China and the southeast of Mongolia. The source I was a relatively 'clean' one and the source II was a 'polluted' one. The dust in PI mainly mixed with the pollutants from the transport pathway, and the dust in PII was rich in pollution compositions and mixed with the resuspended pollutants and the urban dust from the local area in Beijing. The mixing of the dust aerosols originated from a relatively 'clean' source with the pollutants on the transport pathway could carry significant amounts of pollutants downwind. The dust, which came from the 'polluted' source and mixed with the local resuspended pollutants, could deliver much higher content of pollutants downwind. Though the second dust peak was weaker than the first one, it would have greater impacts on the human health for the higher fraction of pollution and water-soluble components. (C) 2006 Elsevier B.V. All rights reserved.