Nighttime reactions of a series of unsaturated alcohols with NO3•: Kinetics, products and mechanisms study

Abstract

Unsaturated alcohols are a class of Biogenic volatile organic compounds (BVOCs) emitted in large quantities by plants when damaged or under adverse environmental conditions, and studies on their atmospheric degradation at night are still lacking. We used chamber experiments to study the gas-phase reactions of three unsaturated alcohols, E-2-penten-1-ol, Z-2-hexen-1-ol and Z-3-hepten-1-ol, with NO₃ radicals (NO₃•) during the night. The rate constants of these reactions were (11.7 ± 1.76) × 10⁻¹³, (8.55 ± 1.33) × 10⁻¹³ and (6.08 ± 0.47) × 10⁻¹³ cm³/(molecule·s) at 298K and 760 Torr, respectively. In contrast, the reaction rate of similar substances with ozone was about 10⁻¹⁸ cm³/(molecule·s), which indicates that the reaction with NO₃• is the main oxidation pathway for unsaturated alcohols at night. Small molecule aldehydes and ketones were the main gas-phase organic products of the reaction of three aldehydes and ketones with NO₃•, and the total small molecule aldehydes and ketones yields can reach between 45%-60%. They mainly originate from the breakage of alkoxy radicals, and different breakage sites determine different product distributions. In addition, the SOA yields of the three unsaturated alcohols with NO₃• were 7.1% ± 1.0%, 12.5% ± 1.9% and 30.0% ± 4.5%, respectively, which were much higher than those of similarly structured substances with O₃ or OH radicals (•OH). The results of high-resolution mass spectrometry shows that the main components of Secondary organic aerosol (SOA) of the three unsaturated alcohols are dimeric compounds containing several nitrate groups, which are formed through the polymerization of oxyalkyl radicals.