Transient SO ₂ uptake dynamics in an atmospheric water aerosol with internal circulation and chemical dissociation

Transient chemical absorption dynamics of sulfur dioxide by a water aerosol droplet at three Reynolds numbers of 0.643, 1.287, and 12.87 are predicted. In this study, a sinusoidal distribution of velocity at the droplet surface is assumed to approach the flow field inside the droplet and a single-phase simulation method (SPSM) is developed to compare with the two-phase simulation method (TPSM). Considering the physical SO ₂ absorption processes with internal circulation, the predictions based the SPSM are very close to those of the TPSM, revealing that the SPSM is a proper method to evaluate the mass transport phenomena for SO ₂ uptake by an aerosol droplet. When chemical reactions in the course of absorption are taken into account using the SPSM, it is noteworthy that the transient absorption process is almost independent of the Reynolds number. This arises from that fact that the entire mass transfer process is controlled by mass diffusion and dominated by the dissociation of sulfurous acid (SO ₂·H ₂O). It is also found that the chemical absorption period is elongated markedly compared to the physical absorption process, approximately by the factors of 5.6-13.1. Eventually, an analysis on the characteristic times of mass transport processes is performed to elucidate mass transport mechanisms and the reasonability of the developed SPSM.