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

Abstract

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.

Wildfire plume ageing in the Photochemical Large Aerosol Chamber (PHOTO-LAC)

“…Other oxygenated aerosol particle constituents reveal temporally different concentration profiles and steadily increase or peak after the first photochemical ageing or after dark ageing. For example, C 10 H 6 O 2 (naphthoquinone), formed from the oxidation of naphthalene, 90 shows its maximum after the first photochemical ageing for both flaming and smouldering BB aerosols. However, many oxygenated species detected by the APPI FT-ICR-MS peak in relative concentrations for the flaming aerosol, but steadily increase during ageing of the smouldering BB aerosol.…”

“…The exported mass spectra were processed by using selfwritten MATLAB algorithms and routines combined in a graphical user interface named CERES Processing. Aer careful investigation and taking into account attribution boundaries from the literature, the following restrictions were deployed for elemental composition assignment for ESI-Orbitrap-MS in the range of 90 For APPI-FT-ICR-MS the following attribution boundaries were applied:…”

Chemical Fingerprinting of Biomass Burning Organic Aerosols from Sugar Cane Combustion: Complementary Findings from Field and Laboratory Studies

“…To resolve the large number of constituents of highly complex OAs, thermal desorption comprehensive two-dimensional gas chromatography hyphenated with time-of-flight mass spectrometry (TD–GC × GC–TOFMS) has been shown to be useful for chemical fingerprinting of the (semi)volatile organic fraction in PM. 26 As a powerful separation technique, GC × GC–MS has been used in several studies 15 , 27 − 29 to effectively detect a wide range of compounds found in BBOAs. For the analysis of GC × GC–MS data, one typically differs between targeted and untargeted analysis.…”