On the Complementarity and Informative Value of Different Electron Ionization Mass Spectrometric Techniques for the Chemical Analysis of Secondary Organic Aerosols

The atmospheric aging of volatile organic compoundsleads to the formation of complex mixtures of highly oxidized secondaryorganic aerosols (SOAs). State-of-the-art mass spectrometry (MS) hasbecome a pivotal tool for their chemical characterization. In this study,we characterized the chemical complexity of naphthalene-derived SOAby three different time-of-flight (TOF) mass spectrometric techniquesapplying electron ionization: high-resolution-TOF-aerosol MS(AMS), direct inlet probe (DIP)-high-resolution TOFMS, and thermaldesorption???comprehensive two-dimensional gas chromatography???TOFMS (GCxGC). We discuss AMS as an online, DIP as an atline,and GCxGC as an offline technique to compare their informativevalue for studying the oxidation state, volatility, and molecularcomposition of laboratory-generated SOA. For GCxGC, the accessibleorganic content was limited to (semi-)volatile compounds andsupported a reliable assignment of the molecular composition. DIP and AMS were used to derive secondary parameters such asO/C and H/C ratios, the general functionality of the compound classes and their abundance upon photochemical aging. Thereby,while the induced pyrolysis in the AMS extended the accessibility range to polar, high-molecular-weight compounds, thermalfragmentation also led to limited molecular information. For DIP, low-volatility compounds could be volatilized and the high massresolution was useful to resolve isobaric mass fragments and assign reliable sum formulas of fragments and molecular ions. Althoughno single technique can provide information to describe the full chemical complexity of the SOA, AMS, DIP, and GCxGC in theircomplementarity are well suited to investigate the impact of SOA on health and environment