Köhler curve ($S_{\mathrm{eq}}(r)$)

The equilibrium saturation ratio over a chemical solution droplet as a function of wet radius for fixed solute content. In the dilute radius approximation $S_{\mathrm{eq}}\simeq 1+A/r-B/r^3$, its maximum occurs at $r_c=\sqrt{3B/A}$. The corresponding critical supersaturation is $2A/(3r_c)$. Diameter and radius coefficients differ and must not be mixed.