Lidar-based investigation of aerosol hygroscopic growth characteristics using fluorescence capacity

The hygroscopic growth of aerosols directly affects their particle size and optical properties, and plays a crucial role in the atmospheric transport and transformation processes, thus serving as an important basis for evaluating environmental and climatic impacts. However, experimental observations on the aerosol hygroscopicity growth characteristics have always been challenging. In this study, the parameter, aerosol fluorescence capacity, is introduced to explore its performance and characteristics in the aerosol hygroscopic growth. Based on a ground-based fluorescence-Raman-Mie lidar system developed by Xi'an University of Technology, the hygroscopic growth properties of aerosol fluorescence capacity are investigated by utilizing synchronous profiles of atmospheric temperature, humidity, backscattering coefficient, and fluorescence capacity. We are focused on the variation trend of the fluorescence capacity hygroscopic growth factor with relative humidity, and discussed its parameterized equation using the Hänel and Brock models, and the results are further compared with the traditional scattering hygroscopic growth factor. Two cloudy cases by lidar are involved in the study, and the results showed that, the fluorescence capacity hygroscopic growth factor can reach 1.82 and 1.60, while, the scattering hygroscopic growth factors were 1.13 and 1.46, respectively; The parameterized fitting results showed that, the Brock model achieved a fitting goodness of 0.94 and 0.98 for the fluorescence capacity hygroscopic growth factor, which were superior to the Hänel model's 0.83 and 0.86; The characteristic parameter κ for the fluorescence capacity hygroscopic growth factor by the Brock model were valued 0.25 and 0.21, significantly higher than those for the scattering hygroscopic growth factor, 0.11 and 0.14. In addition, a continuous lidar detection further indicated, the characteristic parameter κ for the fluorescence capacity hygroscopic growth factor of 0.41 was obtained, which was significantly higher than the κ of 0.19 for the scattered hygroscopic growth factor. The results demonstrated that, compared to the traditional scattering hygroscopic growth factor, the fluorescence capacity hygroscopic growth factor exhibits stronger sensitivity and characterization ability, and can be used as an important optical parameter for evaluating aerosol hygroscopic growth characteristics.