DIFFERENCES IN AEROSOL OPTICAL PROPERTIES AND CORRESPONDING RADIATIVE EFFECTS OF HAZE EVENTS BETWEEN SUMMER AND WINTER IN A MEGA-CITY OF CENTRAL CHINA

Abstract. Aerosol optical properties and corresponding radiative effect (ARE) in ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave (SW) during haze periods between winter and summer of Wuhan were compared. With the development of haze, the average aerosol optical depth (AOD) increased from 0.34 to 0.79 in winter and from 0.64 to 1.36 in summer. The aerosol volume size distribution (ASD) showed that obvious increases in fine mode particles in both winter and summer with haze occurring. The single scattering albedo (SSA) increased significantly in both seasons as a result of the emergence of numerous non-absorbent aerosols when haze occurred. The ARE at UV, VIS, NIR, and SW changed in winter (summer) from −8.29 W/m² to −10.88 W/m² (−8.32 W/m² to −11.06 W/m²), from −43.26 W/m² to −66.04 W/m² (56.33 W/m² to −76.94 W/m²), from −21.90 W/m² to −44.57 W/m² (−31.36 W/m² to −48.67 W/m²), and from −73.46 W/m² to −119.49 W/m² (−8.32 W/m² to −11.06 W/m²) respectively, when air conditions changed from clear to hazy. The variations in ARE fraction of UV, VIS, and NIR in SW depended much more on particle size rather than SSA. The ARE fraction of UV and VIS decreased while it of NIR increased in SW, when haze developed. Back trajectory analysis with active fire areas from Moderate Resolution Imaging Spectroradiometer (MODIS) indicated that the BC originated from the North in summer, while active fires in winter were rare.