The Composition and Stratospheric Fate of Aerosol Particles Originating in the Polar Vortex

Abstract

Stratospheric aerosol plays a significant role in the Earth's energy balance, primarily through its direct interaction with solar radiation. It is also an important chemical reactor that contributes to the multiphase chemistry of ozone destruction by halogen compounds. Sulfuric acid is the main chemical component of stratospheric aerosol, but the processes that control the composition and size of stratospheric particles remain uncertain. We report direct observations of the composition of individual particles of 0.12–1.2 μm geometric diameter, sampled in situ in the high latitude lower stratosphere during February and March of 2023, at altitudes up to 19 km. Polar vortex air was frequently sampled, enabling an investigation into the nature of particles formed in air descending from the mesosphere and upper stratosphere. Over 90% of particles at the sampled sizes in very old polar vortex air contain metals from the ablation of meteors, suggesting that almost all sulfuric acid particles formed in such air grow onto meteoric smoke. Such particles contain extremely low levels of organic matter, typically less than about 0.3% by mass, and relatively high mass fractions of metals, around 5%–8%. These newly characterized “neat” meteoric-sulfuric particles gain additional sulfuric acid and organic compounds by coagulation with background stratospheric aerosol, forming “aged” meteoric-sulfuric particles, which are encountered throughout the stratosphere. On the basis of these observations, we estimate a meteoric iron flux into the Earth's atmosphere of about 0.3–1 Gg yr⁻¹.