10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A Review of Radical Chemistry in Oxidation Flow Reactors for Atmospheric Chemistry Research
ZHE PENG, Jose-Luis Jimenez, University of Colorado-Boulder
Abstract Number: 141 Working Group: Oxidation Flow Reactor: Development, Characterization, and Application to Aerosols
Abstract Oxidation flow reactors (OFR) use oxidants at higher-than-ambient concentrations to simulate atmospheric oxidation processes in shorter experimental times than in the atmosphere. The most common OFR type is, by far, uses OH produced by photolysis of H2O and/or O3 at using Hg lamp emissions at 185 and/or 254 nm. Because of its portability and promise as an alternative to environmental chambers, as well a recent commercial availability, the use of this type of OFRs in both lab and field is increasing extremely rapidly, and may result in a publication output comparable to that of large chambers in a few years. However, since its oxidant generation is similar to stratosphere, skepticism about the relevance of the chemistry OFRs simulate tropospheric oxidation has persisted in the atmospheric chemistry community. During last few years, a series of studies have been carried out to comprehensively investigate the radical chemistry in OFRs, under what conditions it is tropospherically relevant. We will present a review of recent studies on this topic, with a focus on providing OFR experimentalists with clear guidance about inputs and operating procedures to employ and avoid. First, the radical chemistry of HOx, NOy, and organic peroxy radicals (RO2) in OFRs is discussed in terms of their production and loss. OFR conditions are often similar to those in the troposphere as OH dominates against undesired non-OH effects. The key reason why some conditions lead to tropospherically irrelevant/undesired processing of volatile organic compounds (VOCs) is that under some conditions, OH is drastically reduced while non-tropospheric/undesired VOC reactants are not. Common non-tropospheric/undesired VOC reactants are 185 and 254 nm photons, O atoms (O(1D) and O(3P)), NO3 etc. For each of these reactants, we summarize the conditions that enhance their relative importance to OH and the proposed approaches to avoid them, which allow improved OFR experimental design. We also review measures to realize specific experimental goals, the most important one of which is to achieve high-NO conditions. In addition, a number of related experimental issues are discussed, e.g., non-uniformity of UV field, possibility of particle charging by UV, and OH quantification at high precursor and/or aerosol mass loading. In this review, the latest version of estimation equations and OFR Exposure Estimators have been developed and made freely available, and will be briefly described.