The conversion of KCl to K2SO4 (potassium sulfation process) significantly affects ash deposition and corrosion in biomass-fired furnaces. Potassium sulfation has been previously estimated by a detailed gas-reaction chemistry with a simple hypothesis that potassium vapor condenses in a single step. In this study, a detailed aerosol dynamics model is proposed to replace the single-step model of potassium vapor condensation, which is coupled with the detailed gas-reaction chemistry of K-S-Cl to predict the potassium sulfation, particle size distribution, and K2SO4/KCl ratio of different particle sizes. The improved model shows good consistency on the sulfation rate and aerosol formation. The comparison between the calculated and experimental results approves the non-negligible promotion of aerosol formation on KCl(g) sulfation. The sulfation and aerosol formation are calculated at varied SO2 concentrations (100-1000 ppm) with other initial compositions of 100 ppm KCl(g), 5% O-2, 10% H2O, 12% CO2, and balanced N-2. The modeling results show that the mass-based particle size distributions under different cases are generally unimodal. With the increase of the SO2 concentration, the particle size distribution shifts toward a larger scale because of the intensified conversion from KCl to K2SO4. The increase of K2SO4(g) partial pressure in flue gas advances the homogeneous nucleation at a higher temperature, consequently causing a longer time for particle growth. Furthermore, the nucleation and condensation of K2SO4(g) significantly promote the transformation from KHSO4(g) to K2SO4(g), causing an accumulation of K2SO4 in the solid phase and thereby an increased sulfation rate.