(Left) The temperature structure of K2-18b across the range of input H₂S abundances. The Antoine equations for the saturation vapor pressure of sulfur allotropes, H₂O, and C₂H₆ are shown in bold dashed lines, and in lighter colored lines the vapor pressure curves are progressively scaled down from 100% to 100 ppm to illustrate how sulfur allotropes still condense out at trace mixing ratios. (Right) Profiles of gaseous H₂O and condensed S₂ and S₈ in the atmosphere of K2-18b. For H₂O we show only the profile for the 100 ppm H₂S model, and the differences from the H₂O condensation for the other models are insignificant.