Long-Term Investigation of Aerosol Optical and Radiative Characteristics in a Typical Megacity of Central China During Winter Haze Periods

Decadal aerosol characteristics and related radiative effects (ARE) and efficiencies (AREE) at ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave wavelengths were investigated in Wuhan during winter haze periods based on observations from 2007 to 2016. Aerosols changed significantly under haze conditions; the average aerosol optical depth increased from 0.46 to 0.93, and the Angstrom exponent increased from 1.12 to 1.23. Fine-mode particles became dominant, and their peak radius also increased due to hygroscopic growth. The mean value of the UV single-scattering albedo increased from 0.846 to 0.873, revealing the emergence of numerous fine-mode, nonabsorbing aerosols. Backward trajectories suggested that local aerosols were partially affected by transported dust from Northwest China, especially in 2015. The interannual variation of the mean AREE at the top of atmosphere showed a gradually increasing tendency, revealing the enhanced potential cooling capacity of aerosols to the Earth-atmosphere system over Wuhan. The increase in the AREE fraction at UV and VIS wavelengths, and its decrease at NIR wavelengths, indicated that this phenomenon was due to the increased proportion of fine-mode scattering components in aerosols. The variation in AREE at top of atmosphere depended mainly on the single-scattering albedo, while the same variation at the surface depended more on particle sizes. A detailed investigation of aerosols during haze periods can help us to further understand localized climate variations and haze-inducing mechanisms.