ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-8075-2011 The effects of a solar eclipse on photo-oxidants in different areas of China Wu J.-B. 1 5 Wang Z. F. 1 Zhang W. 2 Dong H. B. 1 Pan X. L. 1 Li J. 1 Lin C.-Y. 3 Xie P. H. 4 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Science, Beijing 100029, China Aviation Meteorological Center of China, Beijing 100122, China Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan Key Lab. of Environment Optics & Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, China Graduate University of Chinese Academy of Science, Beijing, China 08 08 2011 11 15 8075 8085 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/11/8075/2011/acp-11-8075-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/8075/2011/acp-11-8075-2011.pdf

This study investigates the effects of the total solar eclipse of 22 July 2009 on surface ozone and other photo-oxidants over China. A box model was used to study the sensitivity of ozone to the limb darkening effect during an eclipse event, and to show that the impact on ozone is small (less than 0.5 %). In addition, the regional model WRF-Chem was applied to study the effects of the eclipse on meteorological and chemical parameters, focusing on different regions in China. Chemical and meteorological observations were used to validate the model and to show that it can capture the effects of the total solar eclipse well. Model calculations show distinct differences in the spatial distributions of meteorological and chemical parameters with and without the eclipse. The maximum impacts of the eclipse occur over the area of totality, where there is a decrease in surface temperature of 1.5 °C and decrease in wind speed of 1 m s<sup>−1</sup>. The maximum impacts on atmospheric pollutants occur over parts of north and east China where emissions are greater, with an increase of 5 ppbv in NO<sub>2</sub> and 25 ppbv in CO and a decrease of 10 ppbv in O<sub>3</sub> and 4 ppbv in NO. This study also demonstrates the effects of the solar eclipse on surface photo-oxidants in different parts of China. Although the sun was obscured to a smaller extent in polluted areas than in clean areas, the impacts of the eclipse in polluted areas are greater and last longer than they do in clean areas. In contrast, the change in radical concentrations (OH, HO<sub>2</sub> and NO<sub>3</sub>) in clean areas is much larger than in polluted areas mainly because of the limited source of radicals in these areas. The change in radical concentrations during the eclipse reveals that nighttime chemistry dominates in both clean and polluted areas. As solar eclipses provide a natural opportunity to test more thoroughly our understanding of atmospheric chemistry, especially that governed by photolysis, a comprehensive experimental campaign during a future solar eclipse is highly desirable.

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