個別粒子分析法から得た黄砂粒子変質成分の短時間変動

抄録

Hourly time scale variation of modified components in individual Asian dust (Kosa) particles was analyzed with double thin film methods combined with time-series samplings. Kosa particles were collected with an impactor at Yasaka, Tango, Kyoto. 3 ∼ 4 days' samplings were run during springtime in 2003 (Run.1) and 2004 (Run.2) , and each one Kosa event could be observed. Several time-series samplings were performed every 3 ∼ 6 hours from the beginning of the Kosa episode. Double thin film methods were utilized to determine the mixing state of sulfate and nitrate, and that of nitrate and chloride in individual aerosol particles. Particles containing SO₄^2- was detected in 25 ∼ 45 % of the coarse particles (50 % cut-off aerodynamic diameter : D₅₀ ≥ 1.2 μm) collected onto each impactor stage at the first Kosa sampling in Run.1. The percentage decreased drastically 6 hours later and particles containing NO₃^- became the dominant species in the modified components. The latter result held for the samples in Run.2 irrespective of the sampling time. Meteorological condition and the results of the simultaneously performed bulk sample analysis in Run.1 implied sulfate in the Kosa particles was formed by the absorption of gaseous SO₂ and the subsequent oxidation in high humidity condition. Percentage of the modified particles roughly decreased with time and that of the particles containing both Cl^- and NO₃^- indicated similar pattern. In each sample, particles containing both SO₄^2- and NO₃^- were hardly detected, which suggests that formation of nitrate and that of sulfate is exclusive.