Impact of Aerosol Mixing State and Hygroscopicity on the Lidar Ratio

The lidar ratio (LR) is a key parameter for the retrieval of atmospheric optical parameters from lidar equations. In this study, we simulated the optical parameters to investigate the impact factors of the LR using a three-component optical aerosol assumption based on the Mie model. The simulated LR was generally related to the overall particle size of the aerosols, the proportion of elemental carbon (EC), as well as aerosol mixing states and hygroscopicity. The LR was positively correlated with the particle size and volume fraction of elemental carbon (f(EC)). The LR increased more than three-fold with the increase in f(EC) from 0% to 40%. The LR of the core-shell (CS) mixing state and homogeneously internal (INT) mixing state was greater than that of the external (EXT) mixing state. The LR of all mixing states increased monotonically with hygroscopicity when the f(EC) was below 10%, while the LR of the core-shell mixing state (homogeneously internal mixing state) initially decreased (increased) and then increased (decreased) with increasing hygroscopicity when the f(EC) was more than 20%. These results will help in selecting a reasonable LR for practical applications.