The chemical composition of stratospheric aerosol particles

Advances in instrumentation can distinguish various types of aerosol particles in the stratosphere and determine their relative abundance. In the background lower stratosphere between major volcanic eruptions, most particles are either relatively pure sulfuric acid, sulfuric acid with material from ablated meteors, or mixed organic-sulfate particles that originated in the troposphere. The meteoric iron and magnesium appear to be dissolved whereas the aluminum and silicon appear to be inclusions. Most stratospheric aerosol mass is liquid sulfuric acid and associated water but a large fraction of particles contain either inclusions of meteoric elements such as silicon or organic material that is probably effloresced or glassy. These solid phases could have large but unknown implications for the ability of particles to act as freezing nuclei for polar stratospheric clouds. Internally mixed black carbon is a measurable but very small component of the stratospheric aerosol by mass. Despite their importance for heterogeneous chemistry, there are few quantitative measurements of halogens in stratospheric particles. The stratosphere offers unique insights into the behavior of organic material in aerosol particles.