Theoretical study on the change of the particle extinction coefficient during the aerosol dynamic processes

In this study, the effects of aerosol dynamics on the aerosol optical properties were analytically investigated using an approximated expression for the overall extinction coefficient (bext), which was valid for a wide range of particle size. The processes of both coagulation and condensation in the continuum region were considered using the moment method, with an overall extinction coefficient obtained from the harmonic mean between the overall particle extinction coefficient of the Rayleigh scattering and geometric scattering regions. The derived analytical expressions were compared with the asymptotic expressions of the extinction coefficient, which showed that the obtained expressions ultimately approached the asymptotic expressions. Subsequently, this study showed a simple and straightforward method for estimating the changes in the extinction coefficient and visibility of polydispersed aerosols during aerosol dynamic processes. The accuracy of the approximated overall coefficient was dependent on a given aerosol refractive index and size parameter. Usually, the error was less than 8% for an average size parameter range of 0–80.