ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-11985-2012 Asian dust storm observed at a rural mountain site in southern China: chemical evolution and heterogeneous photochemistry Nie W. 1 2 Wang T. 1 2 Xue L. K. 2 Ding A. J. 3 Wang X. F. 1 2 Gao X. M. 1 2 Xu Z. 1 2 Yu Y. C. 1 Yuan C. 1 2 Zhou Z. S. 1 2 Gao R. 1 Liu X. H. 6 Wang Y. 4 Fan S. J. 5 Poon S. 2 Zhang Q. Z. 2 Wang W. X. 2 Environment Research Institute, Shandong University, Jinan, China Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China Institute for Climate and Global Change Research, Nanjing University, Nanjing, China School of Environmental Science and Engineering, Shandong University, Jinan, China School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China College of Environmental Science and Engineering, Ocean University of China, Qingdao, China 17 12 2012 12 24 11985 11995 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/11985/2012/acp-12-11985-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11985/2012/acp-12-11985-2012.pdf

Heterogeneous processes on dust particles are important for understanding the chemistry and radiative balance of the atmosphere. This paper investigates an intense Asian dust storm episode observed at Mount Heng (1269 m a.s.l.) in southern China on 24–26 April 2009. A set of aerosol and trace gas data collected during the study was analyzed to investigate their chemical evolution and heterogeneous photochemistry as the dust traveled to southern China. Results show that the mineral dust arriving at Mt. Heng experienced significant modifications during transport, with large enrichments in secondary species (sulfate, nitrate, and ammonium) compared with the dust composition collected at an upwind mountain top site (Mount Hua). A photochemical age "clock" (−Log<sub>10</sub>(NO<sub>x</sub>/NO<sub>y</sub>)) was employed to quantify the atmospheric processing time. The result indicates an obvious increase in the abundance of secondary water-soluble ions in dust particles with the air mass atmospheric processing time. Based on the observations, a 4-stage evolution process is proposed for carbonate-containing Asian dust, starting from fresh dust to particles coated with hydrophilic and acidic materials. Daytime-enhanced nitrite formation on the dust particles was also observed, which indicates the recent laboratory result of the TiO<sub>2</sub> photocatalysis of NO<sub>2</sub> as a potential source of nitrite and nitrous acid.

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