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RESEARCH PRODUCT

Real-time detection of highly oxidized organosulfates and BSOA marker compounds during the F–BEACh 2014 field study

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Abstract. The chemical composition of organic aerosols was analyzed using complementary mass spectrometric techniques during a field study in Central Europe in July 2014 (Fichtelgebirge – Biogenic Emission and Aerosol Chemistry, F–BEACh 2014). Aerosols were analyzed in real-time by Aerosol Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (AeroFAPA–MS), Aerosol Mass Spectrometry (AMS), and Chemical Ionization Atmospheric-Pressure interface Time-of-Flight Mass Spectrometry (CI–APiToF–MS). In addition, offline detection of acidic organic compounds was conducted by non-target screening of filter samples using High Resolution Mass Spectrometry (HRMS) in combination with Ultra-High Pressure Liquid Chromatography (UHPLC). In total, 93 acidic organic compounds were identified as characteristic contributors to the organic aerosol mass at the site. Among the carbon-, hydrogen-, oxygen-containing compounds, several common biogenic secondary organic aerosol (BSOA) marker compounds were detected. High concentrations were found for the monoterpene photooxidation products 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) and 3 carboxyheptanedioic acid, suggesting that α-/β-pinene and d-limonene oxidation products were dominating the organic aerosol fraction. In agreement, volatile organic compound (VOC) measurements showed high mixing ratios for these monoterpenes. Moreover, the high abundance of MBTCA and 3-carboxyheptanedioic acid and their concentration ratios to earlier-generation oxidation products, such as pinic acid, indicate that aged aerosol masses were present during the campaign period. HYSPLIT trajectory calculations revealed that most of the arriving air masses traveled long distances (>1,500 km) over land with high solar radiation, further supporting this hypothesis. Around 47 % of the detected compounds from the filter sample analysis were sulfur-containing, suggesting a high anthropogenic impact on biogenic emissions and their oxidation processes. Among the sulfur-containing compounds, several organosulfates, nitrooxy organosulfates, and highly oxidized organosulfates (HOOS) were unambiguously identified. In addition, correlations among HOOS classes, sulfate and highly oxidized multifunctional organic compounds (HOMs) were investigated. The results support the hypothesis of previous studies that HOOS are formed by reactions of gas-phase HOMs with particulate sulfate. Furthermore, a good agreement was observed between HOOS formation and gas-phase peroxyradical (RO2•) concentrations, measured by the CI–APiTOF–MS. This finding suggests RO2• to be either a direct or indirect precursor for HOOS. In addition, periods with high relative humidity revealed that aqueous-phase chemistry might play a major role in HOOS production.