Stratospheric Particles

Abstract

Particles were collected from the stratosphere by impaction onto specially treated electron microscope screens during six balloon flights in Wyoming in 1972. The submicron diameter particles were predominantly ammonium sulfate near the tropopause and sulfuric acid at higher altitudes, though the ratio of acid to non-acid decreased rapidly with particle diameter, even at the higher altitudes. The acid particles were often, but not always, in a frozen state and aggregates joined in irregular groups were often observed near 20 km altitude. Number concentrations were usually in reasonable agreement with those found by the University of Wyoming's optical counter carried on the same flight, though conspicuously lower concentrations were found near 20 km on two occasions. This is attributed to incomplete collection of frozen aggregates. Size distributions suggested a relatively large number of particles smaller than 0.2? am diameter near the tropopause but few above about 20 km. The distribution of mass with particle diameter implies that an impactor may sometimes underestimate the total mass.