One-component phase diagrams are good approximations to predict pressure-temperature ("P-T") behavior of a substance in the presence of air, provided air pressure is not much higher than the vapor pressure. However, at any air pressure, and from the conceptual point of view, the use of a traditional "P-T" phase diagram is not strictly correct. In this article alternative phase diagrams suitable for systems of one component in the presence of air are proposed. These diagrams are vapor pressure-temperature projections for each total pressure in which a distinctive feature is the absence of a solid-liquid branch. (Contains 1 note and 4 figures.)