A vapor pressure equation for an aerosol is presented here. The latent heat of evaporation (Clausius-Clapeyron contribution), the curvature, and the disjoining pressure effects are considered as the main contributions to the equation. Curvature (Kelvin effect) is shown to be irrelevant. Orientation of the amphiphilic molecules at the surface of the aerosol droplets generates an extra pressure. This pressure, represented here by the structural component of the disjoining pressure, contributes to the Clausius-Clapeyron equation with a nonlinear term proportional to In T. The prediction is in agreement with a recent experimental result.