Significant reduction of surface solar irradiance induced by aerosols in a suburban region in northeastern China

[1] In the spring of 2005, a Sun photometer and a set of broadband pyranometers were installed in Liaozhong, a suburban region in northeastern China. Aerosol properties derived from Sun photometer measurements and aerosol-induced changes in downwelling shortwave surface irradiances are analyzed in this paper. It is shown that the mean aerosol optical depth (AOD) at 500 nm is 0.63. The day-to-day variation of aerosol optical depth is dramatic, with a maximum daily AOD close to 2.0 and a minimum value close to the background level. Dust activities generally produce heavy aerosol loading characterized by larger particle sizes and less absorption than those observed under normal conditions. The reduction of instantaneous direct shortwave surface irradiance per unit of AOD is 404.5 W m(-2). About 63.8% of this reduction is offset by an increase in diffuse irradiance; consequently, one unit increase in AOD leads to a decrease in global surface irradiance of 146.3 W m(-2). The diurnal aerosol direct radiative forcing efficiency is about -47.4 W m(-2). Overall, aerosols reduce about 30 W m(-2) per day of surface net shortwave irradiance in this suburban region.