Wintertime simultaneous measurement and model analysis of fine- and coarse-mode sulfateand nitrate over East Asia

Monday, 15 December 2014
Syuichi Itahashi1, Itsushi Uno2, Xiaole PAN2, Masatoshi Kuribayashi2, Yukari Hara2, Shigekazu Yamamoto3 and Takaaki Shimohara3, (1)Central Research Institute of Electic Power Industry, Tokyo, Japan, (2)Kyushu University, Fukuoka, Japan, (3)Fukuoka Institute of Health and Environmental Sciences, Dazaifu, Japan
Sulfate and nitrate aerosols are major component of PM2.5. In East Asia, it is well known that sulfate aerosols are widely distributed due to large-scale trans-boundary air pollution. For nitrate aerosols, it is considered that fine-mode nitrate can be converted into coarse-mode nitrate on reactions with sea-salt aerosols over East China Sea when transported from China to Japan, however, contributions of trans-boundary air pollution on fine-mode nitrate is not clarified. We observed sulfate and nitrate aerosols on the basis of ACSA (Aerosol Chemical Speciation Analyzer; KIMOTO Electric Co., LTD.) in high-temporal resolution (1 hr) on fine- and coarse-mode at Dazaifu, Fukuoka located in western-part of Japan. Two-way nested (81-27 km) simulation in East Asia by WRF-CMAQ modeling system was developed to investigate the source contributions of fine- and coarse-mode nitrate when the trans-boundary air pollution was occurred. Observed monthly mean concentration in January 2014 at Dazaifu site were 3.41 μg/m3 for fine-mode nitrate, 1.51 μg/m3 for coarse-model nitrate, and 3.81 μg/m3 for fine-mode sulfate. Simulation in fine scale resolution can reproduce the observed concentration with 4.79 μg/m3 (r = 0.60) for fine-mode nitrate, 1.24 μg/m3 (r = 0.51) for coarse-model nitrate, and 3.36 μg/m3 (r = 0.46) for fine-mode sulfate. At urban site in Japan, local-scale contributions are also considered to attribute fine-mode nitrate, and in order to further examine the contributions of trans-boundary air pollution, emission sensitivity analysis with switching off the anthropogenic emissions from Japan was conducted. This sensitivity simulation calculated that monthly mean concentration of 1.19 μg/m3 for coarse-mode nitrate and 3.26 μg/m3 for fine-mode sulfate, suggesting the dominance of trans-boundary air pollution for coarse-mode nitrate and fine-mode sulfate. On the other hand, monthly mean concentration was 1.80 μg/m3 for fine-mode nitrate on sensitivity simulation. That means the contribution from trans-boundary air pollution and local-scale air pollution were respectively 37.6% and 62.4% on monthly mean basis. Temporal variations of contribution of
trans-boundary/local-scale air pollution during the transportation from China to western-part of Japan are further studied, and presented.