Features and Elemental Composition of Mineral Particles Collected in Zhangye, China

Aerosol particles were collected in the spring of 1990 and 1991 and in the summer of 1990 at Zhangye and its surrounding areas in northwestern China and analyzed with an electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer. The weight percentages of elements with atomic numbers larger than 11 (sodium) in individual particles were obtained using EDX spectra. Three samples collected in spring and one sample in summer were analyzed and particle type classifications were given. In spring, mineral particles were present in high number fractions (97-98 %) of particles in the radius range of 0.1-6 μm. Particles mainly composed of aluminosilicate comprised 60-70 % of mineral particles. The samples were characterized by the presence of Ca-rich particles. The Ca-rich particles were present in number proportions (10-20 %) of mineral particles and often contained S, suggesting the presence of CaSO 4 .2H 2 O (gypsum). However, most of the mineral particles had the weight ratios of S/Ca less than 0.1. The analysis showed that Ca-dominant particles, which would be mainly composed of CaCO 3 (calcite), were present mainly in the sub-micrometer radius range. In summer, particles were collected under the atmospheric condition of strong wind (8 ms −1 ). The sample also showed that mineral particles were dominant (98 % by number) in particles of 0.1-5 μm radius. This result suggests the importance of mineral particles, even in the summertime atmosphere.