It is critical to accurately estimate the deposition of inhaled particles in the pulmonary acinus to reduce the damage of ambient aerosols or maximize drug particles' efficacy. However, interparticle interactions were always neglected in the simulation of aerosol deposition in human acinus. A four-generation human acinar model with varying sizes of each generation was developed. Two boundary conditions, rigid wall and moving wall were investigated to simulate the effect of wall motion on the flow field and aerosol deposition for the size range of 0.1–5 μm. Results show that wall motion has a net effect on particles' location and deposition, especially for submicron particles. Moreover, interparticle collisions were employed to gain richer aerosol particle dynamics. Results demonstrate that the minimum concentration of particles for coalescence is 8.5 × 104 particles/cm3 in the acinar region. The coalescence of particles is influenced by particle concentration and diameter, and wall motion and has a non-negligible effect on particle deposition. Furthermore, it should be noted that the influence of collision would be more significant during more respiratory cycles. Our findings demonstrate that wall motion and interparticle collisions play a non-negligible role in the aerosol deposition. • Rigid and moving walls are investigated to simulate the effect of wall motion. • Interparticle collisions and coalescence are employed to gain richer aerosol particle dynamics. • Wall motion and interparticle collisions are proved to affect particle sites and deposition. • The minimum concentration of particles for coalescence is 8.5 × 104 particles/cm3 in the acinar region. • The coalescence of particles is influenced by particle concentration and diameter, and wall motion. [ABSTRACT FROM AUTHOR]