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

J.-B Wu,H B Dong,P H Xie,X L Pan,C.-Y Lin,Z F Wang,W Zhang,J Li

doi:10.5194/acp-11-8075-2011

Abstract

Abstract. 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−1. 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 NO2 and 25 ppbv in CO and a decrease of 10 ppbv in O3 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, HO2 and NO3) 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.

Highlights

Solar eclipses provide a rare and challenging opportunity to investigate how meteorological and photochemical processes respond to abrupt changes in incident solar radiation
Observations of surface ozone Weather Research and Forecasting (WRF)-Chem are depicted in Fig. 7 which shows the differdisplayed a decrease of around 20 ppbv in Hefei, while at ence in 2-m temperature, surface wind speed, NO2, CO, O3, the relatively unpolluted site of Tongcheng the decrease was and NO between Eclipse and NoEclipse conditions for the much smaller
This study investigates the effects on surface ozone and other photo-oxidants of the total solar eclipse of 22 July 2009, focusing on different regions in China

Summary

Introduction

Solar eclipses provide a rare and challenging opportunity to investigate how meteorological and photochemical processes respond to abrupt changes in incident solar radiation. Temperature, solar irradiance, relative humidity, wind and cloudiness within the surface layer are among the most common meteorological parameters explored by previous studies of solar eclipses (Fernandez et al, 1993, 1996; Hanna, 2000; Psiloglou and Kambezidis, 2007; Emde and Mayer, 2007; Kazadzis et al, 2007). Most studies find similar patterns of temperature change, with the lowest values occurring a few minutes after maximum solar coverage, but the reduction experienced may not be directly determined by the magnitude of the eclipse, but by the surrounding environment and local conditions (Founda et al, 2007; Gerasopoulos et al, 2008). Wu et al.: The effects of a solar eclipse on photo-oxidants the stabilization of the surface layer due to the temperature drop (Amiridis et al, 2007)

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Conclusion