Products and mechanism of secondary organic aerosol formation from the reaction of 3-methylfuran with OH radicals in the presence of NOx

Abstract

The aerosol products of the OH radical-initiated reaction of 3-methylfuran in the presence of NOx was investigated in an environmental chamber using a combination of online and offline techniques. Aerosol mass spectra, thermal desorption profiles, O/C, H/C, and N/C ratios, functional group composition, UV absorption spectra, and time profiles of NO, O3, and organic aerosol mass were all consistent with a mechanism of secondary organic aerosol (SOA) formation under dry conditions in which three previously identified unsaturated C5 reaction products, a 1,4-dialdehyde, hydroxyfuranone, and 1,4-aldoacid, partitioned to the aerosol and then underwent acid-catalyzed heterogeneous/multiphase reactions to form two hemiacetals, a cyclic hemiacetal, an ester, and two acetals. SOA formed in the presence of aqueous seed particles appeared to be composed primarily of gem-diol oligomers formed through reactions of unsaturated 1,4-dialdehydes and 1,4-aldoacids with water. Second-generation products of gas-phase OH radical reactions, which should have been a significant fraction of the total products, made at most a minor contribution to SOA. Because unsaturated 1,4-dicarbonyls are major products of the oxidation of aromatic hydrocarbons, the results suggest that although those compounds may form SOA via oligomerization reactions, SOA formation from aromatic hydrocarbons is probably due primarily to other reaction products.