AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Modeling Peroxy Chemistry and VOC Evolution in Oxidation Flow Reactors
ZHE PENG, Julia Lee-Taylor, Marie Camredon, Bernard Aumont, Alma Hodzic, Sasha Madronich, Jose-Luis Jimenez, CIRES, University of Colorado
Abstract Number: 61 Working Group: Aerosol Chemistry
Abstract The use of oxidation flow reactors (OFRs) is very rapidly increasing in atmospheric aerosol chemistry, especially in secondary organic aerosol (SOA) studies. The fate of peroxy radicals (RO2) is a critical step in the oxidation of organics and formation of SOA in the atmosphere. It is critical to characterize the degree to which OFRs and other experimental systems mimic RO2 fates in the atmosphere. The bimolecular fate of most RO2 in standard (“low-NO”) OFR is mainly RO2+HO2, similar to the troposphere. For acylperoxys, their in-OFR loss by RO2+RO2 is not as important as in the troposphere. RO2+NO reactions can dominate for certain “high-NO” modes of operation, although just adding high NO levels at the OFR inlet generally does not work. RO2+OH reactions may be as important in the OFR as they are in the atmosphere, since HO2:OH ratios in OFRs are close to ambient values, but we note the dearth of rate coefficient measurements for this class of reactions. Under typical low-NO conditions, the short residence times of OFRs prevent slower RO2 isomerization (k~0.1 s-1) from proceeding to a similar extent as in the low-NO troposphere. Fast isomerization (k>1 s-1) is much less affected, since it dominates corresponding RO2 fate in both the atmosphere and OFRs under typical low-NO conditions. The similarities and differences of the fate of different VOCs among OFRs, typical experiments in large environmental chambers, and the atmosphere are explored with the fully explicit GECKO-A model. OFRs and chambers can reproduce many aspects of atmospheric OH oxidation, but may differ from the atmosphere in several respects, e.g., relative importance of photolysis and RO2 self/cross-reactions. Most importantly, careful attention to OFR input concentrations and operating conditions is needed, as many commonly-used conditions can lead to chemistry strongly deviating from the atmosphere.