Furoyl peroxynitrate (fur-PAN), a product of VOC–NOx photochemistry from biomass burning emissions: photochemical synthesis, calibration, chemical characterization, and first atmospheric observations

Abstract

The recent increase in frequency and severity of wildfires in the western U.S. has renewed interest in understanding the impact of wildfire emissions on the chemistry of the atmosphere. Furans are a major class of compounds which are important in wildfire emissions and whose atmospheric reaction mechanisms and fates are relatively understudied. One member of that family, the acyl peroxynitrate that is produced from furfural, furoyl peroxynitrate (fur-PAN) is of interest as a potential participant in oxidant and secondary organic aerosol formation, and is a marker for VOC–NO_x photochemistry from wildfire. This work describes a simple photochemical method for synthesizing fur-PAN and demonstrates its detection with thermal decomposition iodide ion chemical ionization mass spectrometry. Fur-PAN has been observed at up to 140 pptv in ambient measurements in Pasadena, CA, in the summer of 2021 during a brief period of wildfire impact at that site, and fur-PAN was well correlated with acryloyl peroxynitrate (APAN), another wildfire photochemical product. Laboratory measurements of fur-PAN thermal decomposition showed it to be similar to other PAN-type compounds and can be described by the Arrhenius expression: k = 3.7 ± 0.2 × 10¹⁶ exp(−(13 700 ± 500)/T) s⁻¹. The solubility of fur-PAN in pure water was also measured and found to be 12.9 ± 0.9 M atm⁻¹ at 295 K, approximately 3–12 times more soluble than other simple alkyl PAN compounds. Thermal decomposition will be a major loss process for fur-PAN in the daytime boundary layer, but there may be a contribution from hydroxyl radical reactions.