Aggregate mass and volume-filling factor vs time for different disk surface densities. The heliocentric distance is 30 au. Panels a and b: mass evolution for 0.1 μm and 1 μm sized monomers, while panels c and d: volume-filling factor evolution. The diamond and the circle indicate when the system becomes drift limited and bouncing dominated, respectively. A square indicates when the aggregates reach St_min = 1.5 × 10⁻³ (Yang et al. 2017). To clearly indicate the case when the system becomes drift limited, the lines continue as dashed lines after this point. An increased gas surface density leads to higher aggregate masses, and vice versa.