Atmo-metabolomics: a new measurement approach for investigating aerosol composition and ecosystem functioning.

Abstract. Aerosols directly and indirectly play crucial roles in the processes controlling the composition of the atmosphere and the functioning of ecosystems. Gaining a deeper understanding of the chemical composition of aerosols is one of the major challenges for atmospheric and climate scientists and is beginning to be recognized as important for ecological research. Better comprehension of aerosol chemistry can potentially provide valuable information on atmospheric processes such as oxidation of organics and the production of cloud condensation nuclei as well as provide an approximation of the general status of an ecosystem through the measurement of certain stress biomarkers. In this study, we describe an efficient aerosol sampling method, the metabolite extraction procedures for the chemical characterization of aerosols, namely, the atmo-metabolome. We used mass spectrometry (MS) coupled to liquid chromatography (LC-MS), gas chromatography (GC-MS) and Fourier transform ion cyclotron resonance (FT-ICR-MS) for a deep characterization of the atmo-metabolome. The atmo-metabolomes from two distinct seasons, spring and summer, were compared to test the sensitivity and demonstrate the information that can be provided from each analytical platform. Our results showed that our sampling and extraction methods are suitable for aerosol chemical characterization with any of the analytical platforms used in this study. The three datasets obtained from these individual platforms showed significant differences of the overall atmo-metabolome between spring and summer. LC-MS and GC-MS analyses identified several metabolites that can be attributed to pollen and other plant-related aerosols. Spring samples exhibit higher concentrations of metabolites linked to higher plant activity while summer samples had higher concentrations of metabolites that may reflect certain oxidative stresses. FT-ICR-MS analysis showed clear differences in the elemental composition of aerosols between spring and summer. Summer aerosols were generally higher in molecular weight and with higher O / C ratios, indicating higher oxidation levels and condensation of compounds relative to spring. Our method represents an advanced approach for characterizing the composition of aerosols that will benefit scientists attempting to understand complex atmospheric processes and the ecosystem status across a whole ecoregion.