Modelling Complex Refractive Indices of Sub-micron Pure and Polluted Dust based on Compositional Sensitive Analysis

Complex refractive index (RI) is an important parameter to determine the radiative effects of aerosol. It is governed by the physico-chemical properties of the aerosol. Scarcity in the detailed information of spectral RI of fine and coarse mode aerosol is challenging and limits our understanding of interaction between aerosol and incoming solar radiation. Marginal data about the RI of aerosol are available for the long-wave radiation that too spatially constrained. In the present study, spectral RIs of pure submicron particles (kaolinite and illite) and polluted particles (comprised of kaolinite, illite, anthropogenic hematite, black carbon (BC), ammonium nitrate and ammonium sulphate) have been modelled for the wavelength range 0.38–21.5 µm using volume mixing rule. Particle aged with anthropogenic hematite shows overall increase in the imaginary part of refractive index ( k ), with increasing concentration of anthropogenic hematite (range 0.10–1.48%). Maximum enhancement in the k value (0.02) observed at 0.38 µm, while minimum k value (0.001) found at 1.2 µm. The complex RIs of aerosol comprised of kaolinite, illite, hematite, BC, ammonium sulphate and ammonium nitrate show “ k ” values ranging from 0.01 to 0.08 for the wavelength range 0.38 to 1.2 µm, while the highest values of 1.5 were observed at wavelength 21.5 µm. Negligible effect was observed in absorption pattern of particle with varying concentration of BC and anthropogenic hematite at wavelength > 2.5 µm.