Kinetics of the reactions of isoprene-derived hydroxynitrates: gas phase epoxide formation and solution phase hydrolysis

摘要

Isoprene, the most abundant non-methane volatile organic compound (VOC)emitted into the atmosphere, is known to undergo gas phase oxidation to formeight different hydroxynitrate isomers in "high-NO"environments. These hydroxynitrates are known to affect the global andregional formation of ozone and secondary organic aerosol (SOA), as well asaffect the distribution of nitrogen. In the present study, we havesynthesized three of the eight possible hydroxynitrates: 4-hydroxy-3-nitroxyisoprene (4,3-HNI) and E / Z-1-hydroxy-4-nitroxy isoprene (1,4-HNI).Oxidation of the 4,3-HNI isomer by the OH radical was monitored using a flowtube chemical ionization mass spectrometer (FT-CIMS), and its OH rateconstant was determined to be(3.64 ± 0.41) × 10 cm molecule s.The products of 4,3-HNI oxidation were monitored, and a mechanism to explainthe products was developed. An isoprene epoxide (IEPOX) – a speciesimportant in SOA chemistry and thought to originate only from"low-NO" isoprene oxidation – was found as a minor, butsignificant, product. Additionally, hydrolysis kinetics of the three synthesized isomerswere monitored with nuclear magnetic resonance (NMR). The bulk, neutral solution hydrolysis rate constantsfor 4,3-HNI and the 1,4-HNI isomers were(1.59 ± 0.03) × 10 s and(6.76 ± 0.09) × 10 s, respectively. Thehydrolysis reactions of each isomer were found to be general acid-catalyzed.The reaction pathways, product yields and atmospheric implications for boththe gas phase and aerosol phase reactions are discussed.