Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance

摘要

Oxidation flow reactors (OFRs) are a promising complement to environmental chambers for investigating atmospheric oxidation processes and secondary aerosol formation. However, questions have been raised about how representative the chemistry within OFRs is of that in the troposphere. We investigate the fates of organic peroxy radicals (RO2), which play a central role in atmospheric organic chemistry, in OFRs and environmental chambers by chemical kinetic modeling and compare to a variety of ambient conditions to help define a range of atmospherically relevant OFR operating conditions. For most types of RO2, their bimolecular fates in OFRs are mainly RO2 + HO2 and RO2 + NO, similar to chambers and atmospheric studies. For substituted primary RO2 and acyl RO2, RO2 + RO2 can make a significant contribution to the fate of RO2 in OFRs, chambers and the atmosphere, but RO2 + RO2 in OFRs is in general somewhat less important than in the atmosphere. At high NO, RO2 + NO dominates RO2 fate in OFRs, as in the atmosphere. At a high UV lamp setting in OFRs, RO2 + OH can be a major RO2 fate and RO2 isomerization can be negligible for common multifunctional RO2, both of which deviate from common atmospheric conditions. In the OFR254 operation mode (for which OH is generated only from the photolysis of added O-3), we cannot identify any conditions that can simultaneously avoid significant organic photolysis at 254 nm and lead to RO2 lifetimes long enough (similar to 10 s) to allow atmospherically relevant RO2 isomerization. In the OFR185 mode (for which OH is generated from reactions initiated by 185 nm photons), high relative humidity, low UV intensity and low precursor concentrations are recom-mended for the atmospherically relevant gas-phase chemistry of both stable species and RO2. These conditions ensure minor or negligible RO2 + OH and a relative importance of RO2 isomerization in RO2 fate in OFRs within similar to x2 of that in the atmosphere. Under these conditions, the ph