Belt radii measured from r²−scaled scattered-light images plotted as a function of stellar age for targets in the CO₂ subsample. Red, yellow and blue shaded regions indicate the temporal evolution of the CO₂ freeze-out zones for stars with masses of 1.5, 2 and 2.3 M_⊙, respectively. The upper and lower boundaries of the freeze-out zones correspond to the BB temperature of 40 and 80 K, respectively. The orange and gray shaded regions are the results of the overlap of the three regions.