CAI formation in time and space. The critical radius (black line) divides this diagram into a region where millimetre grains move inward (due to inward gas motion and radial drift) and a region where these grains are dragged outward with the expanding gas. The light red line encircles the hot T-regulated region with thermally unstable silicates, leading to pure Al-Ca-Ti oxide particles. The cyan shaded area is the region of lasting CAI-formation. The Al-Ca-Ti oxide particles formed in this region will eventually reside in a silicate matrix and populate the disc. Four trajectories for different particle sizes are plotted with green lines.