First detection of molecular hydrate complexes in sulfuric acid aerosols

Abstract

Two un-ionised molecular hydrate complexes, previously observed by Fourier-transform spectroscopy in flat films of vapour deposited sulfuric acid, have been identified directly in aerosols nucleated from SO₃ and H₂O in a 75 dm³ coolable spectroscopic cell. Aerosols of a 1 : 1 complex H₂SO₄·H₂O have been generated at 195 K and have also been formed in cooled liquid sulfuric acid aerosols. A second polymeric metastable hydrate of the type (H₂SO₄.2H₂O)_n has been identified as the initial material formed during the nucleation process of sulfuric acid aerosol at 195 K. These metastable species are likely to play an important role in the formation of sulfuric acid aerosols at the low temperatures found in the upper troposphere and the lower stratosphere.