Coating material-dependent differences in modelled lidar-measurable quantities for heavily coated soot particles

The optical properties of thickly coated soot particles are sensitive to the chemical composition, thus to the refractive index of the coating material. For 58 differently sized coated soot aggregates the extinction-to-backscatter ratio (lidar ratio) and the depolarisation ratio are computed at a wavelength of 355 nm, 532 nm and 1064 nm for two different coating materials: a toluene-based coating and a sulphate coating. Additionally the Ångström exponents between 355 nm and 532 nm as well as between 532 nm and 1064 nm are calculated. The extinction-to-backscatter ratio is found to allow a distinction between the coating materials at all three wavelengths, and the depolarisation ratio allows for a distinction at 355 and 532 nm.