The effects of a solar eclipse on photo-oxidants in different areas of China

Abstract

This study investigates the effects of the total solar eclipse of 22 July 2009 on surface ozone and other photo-oxidants over central China using the WRF-Chem model. Chemical and meteorological observation data were used to validate the model, and results suggest that the WRF-Chem model can capture the effects of the total solar eclipse well. The maximum impacts of the eclipse occur over the area of totality, with a decrease in surface temperature of 1.5 °C and decrease in wind speed of 1 m s<sup>−1</sup>. In contrast, 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 3 ppbv in NO. This study also shows 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. The change in radical concentrations during the eclipse reveals that nighttime chemistry dominates in both polluted and clean areas. In contrast to the effects on atmospheric pollutants, 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 sources of radicals in these areas. In addition, since solar eclipse does provide a natural opportunity to test our understanding more thoroughly on atmospheric chemistry, especially on photolysis-related chemistry, a comprehensive experimental campaign is highly recommended during solar eclipses in future