D.M. Murphy and co-authors present results distinguishing various stratospheric aerosol particles and their components in a new article in the Quarterly Journal of the Royal Meteorological Society. Under background conditions, between major volcanic eruptions, they find that most stratospheric aerosol are either relatively pure sulphuric acid, sulphuric acid mixed with meteoritic material, or mixed organic-sulphate particles originating from the troposphere. Certain meteoritic elements are dissolved in the particles (e.g. iron and magnesium), while others are found as solid phase inclusions. These solid phases could have large but unknown implications in terms of the particles acting as freezing nuclei for polar stratospheric clouds. Find the full abstract here.