Organic aerosols mixing across the tropopause and its implication for anthropogenic pollution of the UTLS

Abstract. Increasing anthropogenic emissions have led to numerous organic compounds in the atmosphere, with uncertain effects on climate, ecosystems, and human health. Particularly, the composition and impact of organic aerosol in the upper troposphere and lower stratosphere (UTLS) remain poorly understood, with few studies addressing the general distribution of aerosols in this layer. In this work, we present a comprehensive analysis of a tropopause fold and convective systems during an airborne campaign over central Europe in summer 2024. We collected filter samples with a multichannel sampler for organic aerosol, effectively separating tropospheric and stratospheric air masses. As a result, we analyzed the chemical composition on a molecular level using ultra-high-performance liquid chromatography coupled with high-resolution Orbitrap mass spectrometry. A subsequent non-target analysis provides novel insights into compositional differences throughout the UTLS. Our findings reveal numerous anthropogenic organic compounds, including C8H19O5PS2 and C15H15NO3S2, alongside dicarboxylic acids, organosulfates, and oxidation products of volatile organic compounds found in stratospheric samples. Additional target analysis identifies pollutants like perfluorooctanoic acid and tris(2-chloropropyl) phosphate that redistribute from the ground. These findings underscore the importance of transport processes to high altitudes and the growing impact of anthropogenic pollution, contributing to a better understanding of the relationship between emissions, the chemical composition of the UTLS, and climate effects.