Atmospheric supersaturation
= Atmospheric supersaturation
{title2=$s=p_v/p_{\rm sat}(T)-1$}
The fractional excess of water-vapor <pressure> above equilibrium saturation over a flat pure-water surface at the same <temperature>: $s=p_v/p_{\rm sat}(T)-1$. Positive $s$ can drive droplet growth, but activation of a particular <aerosol> particle requires exceeding its <critical supersaturation>. Cooling, condensation and mixing jointly determine parcel supersaturation.