Numerical simulation of the microphysics and liquid chemical processes occur in fog using size resolving bin scheme

Abstract

This research aims to understand the role of the initial hygroscopicity of aerosol particles, scavenging mechanisms and of aqueous chemistry in the evolution of the aerosol size distribution. A box model with a size resolving moving bin scheme is used to simulate the fog events over Budapest (Hungary) and Delhi (India). The results from the study are as follows: (i) Aerosol particles can be washed out from the atmosphere more efficiently by Brownian and phoretic scavenging than by activation processes. The efficiency of scavenging mechanisms depends on the size distribution of the dry aerosol particles and the size dependence of the hygroscopicity of the aerosol particles. The efficiency of the phoretic scavenging is also impacted by the duration of the dissipation phase of the fog. (ii) The liquid-phase chemistry, which occurs inside the droplets due to their long residence times in the atmosphere, significantly impacts the size distribution of the regenerated particles. (iii) The liquid-phase chemistry also impacts the hygroscopicity of the regenerated aerosol particles. The enhancement of the concentrations of NH4+, NO3− and S(VI) ions inside the droplets result in a substantial increase of the hygroscopicity of the water-soluble particles. This higher hygroscopicity may impact the fog dissipation by increasing the solution effect and helps to uphold successive fog events under favorable environmental condition.