Hygroscopic growth characteristics of anthropogenic aerosols over central China revealed by lidar observations

Abstract. Lidar-derived particle backscatter coefficient is commonly used to assess air pollution levels; however, hygroscopic growth can amplify particle backscatter and hinder accurate assessment of particle concentration. This study investigated the hygroscopic growth characteristics of urban anthropogenic aerosols in Wuhan (30.5° N, 114.4° E), central China, using ground-based 532-nm polarization lidar observations during 2010–2024. A total of 192 cases were identified based on the following criteria: (1) the presence of a layer thicker than 300 m; (2) a lidar-derived backscatter coefficient that increases monotonically with simultaneously-measured relative humidity (RH) from radiosonde, and (3) limited variations in key meteorological parameters, including water vapor mixing ratio, potential temperature, and wind speed and direction. Using the Hänel parameterization method, the hygroscopic growth parameter γ was estimated as 0.62 (±0.24), corresponding to a backscatter coefficient enhancement factor of 2.36 at 85 % RH. No evident differences in γ were observed between the boundary layer (0.63±0.25) and free troposphere (0.60±0.24). The annual mean γ increased from 0.49 in 2014 to 0.63 in 2017 and stabilized within 0.6–0.7 after 2018, closely following the evolution of the annual mean NO₂-to-SO₂ concentration ratio. The minimum seasonal average γ occurred in winter (0.56), while the maximum was observed in autumn (0.64). These results provide a comprehensive characterization of the long-term and seasonal hygroscopicity of pollutants over central China, enhancing our understanding of the influence of hygroscopic growth on lidar-observed particle backscatter coefficients and offering valuable insights for urban air pollution control strategies.