Ion nucleation—a potential source for stratospheric aerosols

Abstract

The stratospheric aerosol layer is of considerable interest for its potential influence, at least temporarily, on the Earth's radiation budget and climate¹. While the nature of the aerosol is now reasonably well established the mechanisms leading to the formation of new particles are poorly understood^2–4. It is thought that the aerosols are formed by heterogeneous heteromolecular condensation involving sulphuric acid and water vapour and pre-existing condensation nuclei (CN) of tropospheric or meteoric origin. The resulting supercooled solution droplets which are composed of ∼75% (by mass) H₂SO₄ and 25% H₂O undergo condensational and coagulational growth and are ultimately removed from the stratosphere by gravitational sedimentation. CN-formation in the stratosphere by homogeneous or ion nucleation (IN) has largely been found to be inefficient^2–6. I have now investigated the role of ion nucleation in stratosphere aerosol formation in the light of recent progress in both the areas of stratospheric ion composition⁷ and sulphuric acid vapour^8–10 measurements. In constrast to previous conclusions ion nucleation is found to be a potential source for stratospheric aerosols.