The mineralogy and possible sources of spring dust particles over Beijing

A severe Asian Dust Storm (ADS) event occurred on 16-17 April 2006 in northern China. The mineral compositions of dust samples were analyzed using X-ray diffraction (XRD). The results indicated that dust particles of the 17 April 2006 dust storm were dominated by quartz (37.4%) and clay (32.9%), followed by plagioclase (13.7%), with small amounts of calcite, K-feldspar, dolomite, hornblende and gypsum (all less than 10%). The clay fractions with diameter less than 2 mu m were separated from the dust storm particles by centrifuging and were further analyzed by XRD. The results revealed that the clay species were mainly illite/smectite mixed layers (I/S) (49%) and illite (34%), with small amount of kaolinite (8%) and chlorite (9%). In order to evaluate the feasibility of using the mineralogy to trace the sources of dust particles, the XRD results of the 17 April 2006 dustfall particles were compared with the dust particles over past years. The results confirmed that the finer dust particles represented by the ADS PM10 displayed a smaller quartz/clay ratio than the dustfall particles. The dust storm particles, either from the ADS PM10 or from the 17 April 2006 dustfall, showed a lower level of dolomite contents and lower dolomite/clay ratios compared with the non-dust storm dustfall particles. This implies that dolomite could be used to distinguish between the dust contributions from local and non-local sources. Similar trends were found for the gypsum and the gypsum/clay ratio. Moreover, the two dustfall samples had a lower level of illite/smectite mixed layers and a higher level of illite than airborne PM10, implying that the dustfall particles tend to be enriched with illite in its clay fraction.