Air Pollution Unable to Intensify Storms via Warm-Phase Invigoration

Abstract

According to the hypothesis of aerosol invigoration, the higher concentration of aerosols in polluted air intensifies storms. A leading theory for explaining such a relationship is warm-phase invigoration, in which cloudy updrafts that are more polluted more readily condense water vapor onto liquid drops, thereby releasing latent heat faster, leading to higher buoyancies and higher updraft speeds. For this mechanism to work, water-vapor supersaturations well in excess of 1% must be typical of relatively unpolluted cloudy updrafts. Here, the supersaturation is calculated from in situ observations of warm-phase cloudy updrafts over the Amazon. Instead of values well in excess of 1%, the typical values are found to be around 0.2%. These observations imply that cleaner preindustrial air might have generated supersaturations around 1%, but those are still too low for warm-phase invigoration to have any practically significant impact on cloud buoyancy and updraft speeds.