O3 chemistry of 2,5-dimethylfuran: mechanism development†

Furans are emitted from biomass burning (BB) and contribute to the reactivity of BB plumes with a significant proportion. Consequently, the development of comprehensive furan oxidation schemes is one of the crucial elements towards a better understanding of BB plume chemistry. Nighttime oxidation is supposedly dominated by NO₃ radicals and O₃. The present study has chosen 2,5-dimethylfuran (25DMF) as a model compound for the development of an O₃ oxidation mechanism for furans. Experiments were performed in the QUAREC atmospheric simulation chamber (QUAREC ASC) at 299 ± 2 K and a pressure of 980 ± 20 mbar under dry conditions (relative humidity < 0.1%) targeting the reaction kinetics, the OH formation and the oxidation mechanism. The reactions were monitored by long-path FTIR spectroscopy and a PTR-ToF-MS instrument. We determined a rate coefficient of (3.3 ± 1.0) × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹ for the target reaction using the relative-rate method. An OH yield of 25 ± 10% was obtained when using 1,3,5-trimethylbenzene as an OH tracer. Reaction products are formaldehyde, methyl glyoxal, ketene, glyoxal, methyl hydroperoxide, acetic anhydride, and acetic acid, respectively. The methyl glyoxal, glyoxal and formaldehyde yields were found to be sensitive to the overall peroxy radical level in the system. The PTR-MS data indicate further reaction products, which are tentatively assigned. A mechanism is postulated to account for the clearly identified reaction products. Overall, the obtained results indicate that O₃ oxidation of furans might contribute to acidity in nighttime BB plumes.