| Summary: | Ice cores are environmental archives that are used to reconstruct past changes in the atmospheric aerosol composition. Most ice-core studies have focused mainly on inorganic species and a few dozen organic molecules. However, organic compounds can account for up to 90% of the aerosol composition, meaning that only a fraction of the organic constituents has been studied, limiting our understanding of past atmospheric aerosol chemistry changes. Here, we present the first non-target screening ice-core record investigating the molecular composition of the Belukha ice core (Altai, Russian Federation) over the 1830-1980 CE period. We identified 491 molecules, mainly constituted by aliphatic secondary organic aerosol (SOA) species (e.g., dicarboxylic acids, ketoacids…) consisting of carbon, hydrogen, and oxygen atoms. Since 1955 CE, the ice-core molecular composition has changed with higher occurrence of nitrogen and sulfur-containing compounds, either associated to enhanced atmospheric reactions with anthropogenic-sourced NOx and SO2 or linked to direct emissions. During this period, we also observed an increase in the SOA oxygen-to-carbon ratio and average carbon oxidation state, suggesting an increase in the oxidative capacity of the atmosphere.
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