Importance of Asian dust acid uptake for the dust-nitrate transboundary pollution from East Asia to Japan area

　We observed the 1-h resolution fine (particle diameter less than 2.5μm) and coarse (particle diameter between 2.5‒10μm) mode NO3- and single particle (0.5‒10μm) number concentrations during the long-lasting yellow sand episode that occurred from May‒June, 2014, in Fukuoka, and showed that both the fine and coarse NO3- concentrations strongly correlated with the coarse mode particles PMc (particle diameter between 2.5‒10 μm) which is dominated by the yellow sand.
　This indicated that the NO3- was generated from the HNO3 gas by the heterogeneous reaction on the surface of the yellow sand particle (forming the dust-nitrate) and transported as Ca(NO3)2. A chemical transport model including the dust acid uptake processes reproduced both the observed dust and fine/coarse NO3- time variations. A source-receptor analysis for the origin of the observed dust-nitrate in Fukuoka showed that the 70‒80％ of the dust-nitrate originated from the NOx emission over the wide regions from Beijing to Shanghai, China, and the contribution of the Japanese NOx emission was less than 11％. Both observations and a numerical analysis showed that the coarse mode dust-nitrate fraction is larger than the fine-mode dust-nitrate. A chemical transport model analysis also indicated that the fine-mode dust-nitrate is an important fraction of the observed fine NO3- and showed that the dust-nitrate is also important for PM2.5 air pollution.

　For more information about this research, see;
Numerical Analysis of Trans-Boundary Transport of Dust-Nitrate during the Long-Lasting Yellow Sand Episode Observed over the Northern Kyushu Area in Late May‒Early June 2014.
J.Jpn. Soc. Atmos. Environ, 51, pp. 181 – 189 (2016) (in Japanese)

Left: Total dust and dust-nitrate concentration for May 27 and May 28, 2014.

Right: Model simulated source-receptor relationship of (upper) fine-mode and (lower) coarse mode dust-nitrate at Fukuoka.