Elemental composition and mixing properties of atmospheric mineral particles collected in Hohhot, China

Abstract

Aerosol particles were collected during the period from 23 to 28 April 1991 at Hohhot in the Inner Mongolia Autonomous Region of China, which is in an urban area located near one of the source areas of atmospheric mineral particles. The four samples were examined by a transmission electron microscope equipped with an energy-dispersive X-ray (EDX) analyzer to obtain the size and elemental composition of individual mineral particles. On the basis of EDX analyses for 385 particles, mineral particles were present in an extremely high number (98%) of particles in the radius range of 0.1–3 μm. Particles mainly composed of silicates comprised 70% of mineral particles. “Ca-rich” particles were detected in 18% of all the particles. Most of Ca would be present as CaCO 3, although the internal mixture of CaCO 3 and CaSO 4 was also found. Particles mainly composed of halite (NaCl) were present in low percentages of about 2% of mineral particles, and most of the particles were modified. The sample collected in the situation of weak wind contained spherical fly ash particles with about 13% of the particles analyzed. For the samples other than this sample, the grand abundance of mineral particles other than fly ash particles was larger than 98%. The hygroscopic properties of mineral particles were examined by the dialysis (extraction) of water-soluble material with distilled water. The sample collected in the situation of anthropogenic influence showed the presence of water-soluble material in mineral particles. On the basis of the EDX analysis and the water dialysis, it is suggested that the formation of CaSO 4 has occurred through chemical reactions of CaCO 3 in mineral particles with sulfuric acid in the atmosphere of Hohhot.