Overview of Long-Lasting Yellow Sand and High Concentration of Air Pollution observed over the Northern Kyushu Area in late May–early June 2014

Abstract

The Kyushu area was covered by a long lasting (～7 days) yellow sand and high concentration of air pollution from late May to early June 2014. This episode originated by the two dust events that occurred in the inland desert area of China, then the long-range transported dust and air pollutants are trapped under the blocked high pressure system. Intensive field observations based on the advanced aerosol measurement instruments placed at Kyushu University (Chikushi Campus) successfully observed the physical and chemical changes of this long-lasting episode and simulated by the GEOS Chem chemical transport model (CTM). The CTM reproduced the time variation of the SO₄^2- and NH₄⁺quite well, however, the modeled NO₃^- variation showed an unrealistic diurnal variation that is related to the gas-aerosol equilibrium module and meteorological parameters. The model sensitivity experiment and observational data analysis showed that 88% of the SO₄^2- was transported from outside of Japan. We confirmed that the coarse-mode NO₃^- had an elevated concentration during the first stage of the yellow-sand transport period, and 70–80% of this elevated tNO₃ was transported from outside Japan.