Optical properties of internally mixed ammonium sulfate and soot particles--a study of individual aerosol particles and ambient aerosol populations.

Optical parameters of simulated ambient individual ammonium sulfate and soot-mixed particles were calculated using the discrete-dipole approximation method with different model geometries. Knowledge of the mixing state and the approximation by a suited idealized geometry reduces the errors of the optical properties by +/-50% to +/-10%. The influence of the soot content and the mixing state on the optical properties of the total aerosol was estimated. For the total aerosol population, the size distribution and the absolute soot content had the largest influence. The exact geometry of the ammonium sulfate and soot-mixed particles can be neglected.