Characterizing Organic Stratospheric Aerosols by Functional Group Analysis from the SABRE 2023 Campaign

Stratospheric aerosols play a crucial role in atmospheric chemistry and climate through heterogeneous chemical reactions and radiative forcing. Although sulfate aerosols in the stratosphere have been extensively studied, the organic fraction remains poorly characterized, despite its potential importance for both climate and chemical processes.

The Stratospheric Aerosol Processes, Budget, and Radiative Effects (SABRE) 2023 campaign deployed the WB-57 high-altitude aircraft with a payload designed to improve characterization of stratospheric aerosols. Aerosol particles with aerodynamic diameters between 0.18 and 3.2 μm were collected using a cascade impactor (Mini-MOUDI 135, MSP) for offline analysis. We apply Scanning Transmission X-ray Microscopy coupled with near-edge X-ray absorption fine structure (STXM-NEXAFS) to characterize the composition and morphology of individual stratospheric aerosol particles. Carbon K-edge spectra are used to classify particles by organic carbon, elemental carbon, and inorganic content, enabling investigation of aerosol mixing state, morphology, and carbon functional group distributions. NEXAFS analysis also measures potential tracers, such as potassium associated with biomass burning, and other anthropogenic organic species. Using a radial distance shell-based classification scheme, we present preliminary results highlighting the complexity and diversity of particle morphologies. These microphysical properties help constrain the impacts of stratospheric aerosols on radiative forcing and ozone chemistry. We compare results across multiple flights, distinguishing aerosols sampled within and outside the polar vortex. Together, these observations advance our understanding of the chemical and radiative roles of stratospheric aerosols in Earth’s atmosphere.