Laboratory characterization of furan, 2(3H)-furanone, 2-furaldehyde, 2,5-dimethylfuran, and maleic anhydride measured by PTR-ToF-MS

Furanoids are significant contributors to volatile organic compound hydroxyl radical reactivity in biomass burning emissions, yet their accurate measurement using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) remains challenging due to potential interferences and measurement uncertainties. In this study, we conduct detailed laboratory characterizations of furan (C₄H₄O, protonated m/z 69.033), 2(3H)-furanone (C₄H₄O₂, m/z 85.028), 2-furaldehyde (C5H₄O₂, m/z 97.028), 2,5-dimethylfuran (C6H8O, m/z 97.065), and maleic anhydride (C₄H₂O₃, m/z 99.008). Sensitivities for these compounds were found to have minimal dependence (less than 15 %) on both sample humidity and drift tube electric field strength (E/N). At high E/N (150 Td), fragmentation was observed for 2-furaldehyde (∼ 8 %) at m/z 69.033, potentially interfering furan measurements, while hydrolysis products corresponding to m/z+18 ions were detected for 2(3H)-furanone, 2-furaldehyde, and maleic anhydride. The hydrolysis of maleic anhydride to maleic acid is most prominent, with the hydrate accounting for 7 %-31 % of the parent ion signal across E/N conditions. Gas standard recertification confirmed the long-term stability of furanoids, and 21 other VOCs, in compressed gas mixtures, with changes in mixing ratios of less than 5 % over seven years, although PTR-ToF-MS instrument sensitivities decreased by ∼ 30 % during this time, likely due to aging of the microchannel plate (MCP). While the stability of gas standards and the minimal humidity and fragmentation effects support the accurate measurement of furanoids by PTR-ToF-MS, discrepancies with co-deployed gas chromatography-mass spectrometry highlight the need to further investigate potential isomeric and fragment interferences, particularly in aged BB smoke.