Sensitivity analysis of the ngstrom exponent for multimodal aerosol size distributions

This study characterizes the ngstrom exponent for polydispersed aerosol size distributions. Under the assumption of a lognormal size distribution, the dependence of ngstrom exponent on the size distribution and the refractive index with varying real and imaginary parts are determined. Further, the influence of coarse mode particles on the ngstrom exponent is investigated quantitatively. The results show that the nuclei mode has less influence under the simulation conditions considered in this study. It is also shown that the refractive index is an important factor influencing the ngstrom exponent. The effect of the coarse mode on the ngstrom exponent computed with different aerosol number concentrations and as a function of a geometric standard deviation and a geometric mean diameter is tested. It is shown that the coarse mode is crucial for determining the ngstrom exponent.