Fig. 2.
Height z vs. grain radius s where τr = 1 at r = 1 au. The peak of the z coordinate of τr defines the height of the exposed layer z1 and the radius s1 up to which grains contribute to the opacity in the exposed layer (red arrows). Grains larger than s1 are too settled to contribute. The size sgeo is an upper limit for s1 as the opacity decreases with larger grain sizes.
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