The Stratospheric Aerosol Layer and Anhydrous Reactions Between Ammonia and Sulfur Dioxide1

Abstract

Past studies of the reactions between anhydrous NH3 and anhydrous SO2 have suggested that two distinct products are formed. These products are stable below about 10C, are pale yellow or white solids, and have NH3:SO2 stoichiometric ratios of 1:1 and 2:1, respectively. The present work corroborates these results and presents quantitative measurements of the equilibrium total vapor pressure over the products at temperatures between −10 and −70C. Infrared spectra of the vapor infer that the products dissociate reversibly on sublimation into their components, NH3 and SO2. One white product was formed which exerted an extremely low vapor pressure at low temperatures. Regions of temperature minima would be preferred for its formation in the atmosphere. This stable product may appear at some stage in the formation of the ammonium sulfate layer in the lower stratosphere.