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 compounds leads to the formation of complex mixtures of highly oxidized secondary organic aerosols (SOAs). State-of-the-art mass spectrometry (MS) has become a pivotal tool for their chemical characterization. In this study, we characterized the chemical complexity of naphthalene-derived SOA by three different time-of-flight (TOF) mass spectrometric techniques applying electron ionization: high-resolution–TOF–aerosol MS (AMS), direct inlet probe (DIP)–high-resolution TOFMS, and thermal desorptioncomprehensive two-dimensional gas chromatographyTOFMS (GC × GC). We discuss AMS as an online, DIP as an atline, and GC × GC as an offline technique to compare their informative value for studying the oxidation state, volatility, and molecular composition of laboratory-generated SOA. For GC × GC, the accessible organic content was limited to (semi-)­volatile compounds and supported a reliable assignment of the molecular composition. DIP and AMS were used to derive secondary parameters such as O/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, thermal fragmentation also led to limited molecular information. For DIP, low-volatility compounds could be volatilized and the high mass resolution was useful to resolve isobaric mass fragments and assign reliable sum formulas of fragments and molecular ions. Although no single technique can provide information to describe the full chemical complexity of the SOA, AMS, DIP, and GC × GC in their complementarity are well suited to investigate the impact of SOA on health and environment.