Neutralization of calcite in mineral aerosols by acidic sullur species collected in China and Japan studied by ca K-edge X-ray absorption near-edge structure.
Calcium species in mineral aerosols collected simultaneously in Aksu (near the Taklimakan Desert), Qingdao (eastern China), and Tsukuba (Japan) during dust and nondust periods were determined using Ca K-edge X-ray absorption near-edge structure (XANES). From the fitting of XANES spectra, it was found that (i) calcite and gypsum were the main Ca species in the aerosol samples, and (ii) the gypsum fraction versus total Ca minerals [Gyp]/[Ca2+]t increased progressively in the order Aksu < Qingdao < Tsukuba. Surface-sensitive XANES in the conversion electron yield mode (CEY) showed that the gypsum is formed selectively at the surface of mineral aerosols for all the samples except for that taken in Aksu during the dust period. The decrease of the [Gyp]/[Ca2+]t ratio with an increase in particle size showed that the neutralization effect proceeds from the particle surface. For the Aksu sample in the dust period, however, (i) the [Gyp]/[Ca2+]t ratios obtained by XANES measured in the fluorescence (FL; regarded as bulk analysis) and CEY modes were similar and (ii) size dependence was not found, showing that neutralization is not important for the sample because of the large supply of mineral aerosol with little neutralization effect in Aksu. It was also found that the pH of the aerosol and the ratio of (NH4)2SO4 to gypsum were positively and negatively correlated with the Ca (or calcite) content, respectively. The speciation of Ca by XANES revealed the neutralization processes of acidic sulfur species by calcite during the long-range transport of mineral aerosols.
Takahashi
Yoshio
Y
Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan. ytakaha@hiroshima-u.ac.jp
Miyoshi
Takuro
T
Higashi
Masayuki
M
Kamioka
Hikari
H
Kanai
Yutaka
Y
D000336:Aerosols; D000392:Air Movements; D000393:Air Pollutants / Q000737:chemistry*; D002119:Calcium Carbonate / Q000737:chemistry*; D002133:Calcium Sulfate / Q000737:chemistry; D055598:Chemical Phenomena; D002681:China; D004391:Dust / Q000032:analysis*; D004784:Environmental Monitoring; D007564:Japan; D013057:Spectrum Analysis / Q000379:methods; D013457:Sulfur Compounds / Q000737:chemistry*; D014965:X-Rays
D000336:Aerosols; D000393:Air Pollutants; D004391:Dust; D013457:Sulfur Compounds; D002119:Calcium Carbonate; D002133:Calcium Sulfate