Correlation between atmospheric O4 and H2O absorption in visible band and its implication to dust and haze events in Shanghai, China

Abstract Ground-based zenith-sky DOAS observation was carried out from October 1, 2009 to September 30, 2010 in Shanghai, China to measure the O 4 and H 2 O absorption in visible band and to illustrate the dependence of their correlation slope on the aerosol pollution type. Good correlations between O 4 and H 2 O DSCDs can be found through linear regression analysis whether it was sunny, cloudy, overcast, or rainy. The correlation slope varied seasonally in the order of summer   sunny > cloudy > overcast > rainy. The implication of the variation of slope to the aerosol pollution type was discussed for typical heavy dust and haze episodes occurred in March 2010 and October 2009, respectively. As the correlation slope abruptly increased during the heavy dust due to low moisture content and enhanced O 4 absorption caused by abundant suspended dry crustal particles, the slope dropped suddenly in the haze episode owing to the significant augment of H 2 O absorption. Thus, the much discrepant correlation patterns may be regarded as a characteristic signature for dust and haze events.