Non-Target Analysis of Atmospheric Organic Aerosols as a Tool to Discriminate Anthropogenic Contribution in Mixed Air Masses during the ACROSS campaign

Abstract. Organic aerosol is a major component in the particle phase of Earth´s atmosphere and has influences on quality of life, health and climate. In this study, a non-target analysis of the chemical composition of atmospheric organic aerosols using liquid chromatography-Orbitrap mass spectrometry (LC-Orbitrap MS) was conducted to differentiate anthropogenic and biogenic sources through unsupervised KMeans clustering. The ACROSS campaign dataset (consisting of 36 wind-characterized samples) identified 4,916 compounds (in the range 50–400 m/z). Due to the location of the sampling site, the samples contain influences from the greater Paris area, as well as biogenic influences from the surrounding forest. K-means clustering, constrained to 2,917 compounds with strong wind-direction correlation, resolved distinct biogenic and anthropogenic clusters. Biogenic aerosols were dominated by CHO compounds (H/C: 1.2–1.7; O/C: 0.15–0.7), consistent with oxidized terpenes, while anthropogenic aerosols featured significant CHOS enrichment (H/C: 1.5–2.2; O/C: 0.2–1.0), including nitrogen-sulfur aromatics (e.g., C₁₀H₁₈NO₈S⁻ with nitro/sulfonic groups and aromatic fragments). The approach allows to quantify anthropogenic contribution in mixed air masses, demonstrating higher amounts of anthropogenic compounds ratios during Paris-influenced periods. Results validate wind-driven source apportionment for small sample size non-target studies, providing a transferable method for aerosol characterization.