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 μm 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.