On the Possibility of Formation of Ammonium Sulfate Particles in the Stratosphere

Abstract

The possibility of formation of ammonium sulfate particles in the stratosphere is examined by comparing the absorption rate of ammonia gas into a sulfuric acid droplet with the condensation rate of sulfuric acid vapor onto the droplet. When the concentration of ammonia gas is sub-ppb level, the conversion time from a sulfuric acid droplet of 0.1μm radius into an ammonium sulfate particle is one to two orders of magnitude shorter than the characteristic time scales of eddy diffusion and sedimentation of particles of 0.1μm radius in the stratosphere. The contribution of coagulation to the growth of particles is smaller than that of the condensation and negligible. When the concentration of ammonia gas is low enough for the influence of the absorption to be neglected, the conversion time from an ammonium sulfate particle of 0.1μm radius into an entire liquid droplet is comparable to or longer than the characteristic time scale of eddy diffusion and sedimentation in the stratosphere.