Time evolution of the dust-to-gas ratio in the vicinity of a pressure bump with amplitude A = 0.4. Compared from left to right are different metallicities Z = 0.01, 0.03, 0.05 with the same τ₀ = 4 × 10⁻³. The over-plotted solid curves are the mid-plane gas pressure at times indicated by horizontal dashed lines. The dashed curves are the initial gas pressure for comparison. The arrows indicate the direction of dust movement as predicted by Eq. (36) and are all normalized to have the same length.