Identification of Individual Si-Rich Particles Derived from Kosa Aerosol by the Alkali Elemental Composition

摘要

A method of scanning electron microscopy-energy dispersive X-ray microanalysis (SEM-EDX) has been investigated for the identification of individual Si-rich particles derived from Kosa aerosol. The elemental composition of individual Si-rich particles (α-quartz) having SiO_2 content over 80% was determined by SEM-EDX using a standardless φ(pz) correction program, and the results were normalized to 100% on the basis of oxide composition. The distribution of (Na_2O + K_2O)/SiO_2(%) in individual Si-rich particles from real airborne particulate matters showed a sharp and clear seasonal variation. It was found that the distribution was closer to those in the China loess and desert sand in spring time compared to those of the non-Kosa aerosol, the distribution could be successfully used as an effective indicator. The distribution of (MgO + CaO)/SiO_2(%) was also used for discrimination from Si-rich particles in some Japanese volcanic rocks such as Andesites. Individual Si-rich particles derived from Kosa aerosol were clearly discriminated from those derived from the Japanese igneous rocks by the proposed method. These results suggest that the alkali elemental composition of individual Si-rich particles is a useful indicator to identify the Kosa particles and to investigate transportation of the Kosa aerosol.