AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Oxidation Flow Reactors (OFRs): Highlights of Recent Modeling and Field Studies
BRETT PALM, Rui Li, Zhe Peng, Weiwei Hu, Amber Ortega, Pedro Campuzano-Jost, Douglas Day, Harald Stark, Jason Schroder, Joost de Gouw, William Brune, Jose-Luis Jimenez, University of Colorado
Abstract Number: 590 Working Group: Aerosol Chemistry
Abstract Oxidation flow reactors (OFRs) are popular tools for studying SOA formation and aging. In an OFR, high oxidant concentrations (OH, O$_3, or NO$_3) can be reached, leading to hours–months of equivalent atmospheric oxidation during the several-minute OFR residence time. We present highlights from recent OFR modeling studies and use them to interpret OFR field measurements of SOA formation and aging. HOx, Ox, and photolysis chemistry was modeled for two common OH production methods (utilizing 185+254 nm UV light, or 254 nm only). OH exposure (OH$_(exp)) can be estimated within a factor of ~2 using model-derived equations, and is strongly dependent on external OH reactivity, which may cause significant OH suppression in some circumstances (e.g., lab/source studies with high precursor concentrations). UV light photolysis and reaction with oxygen atoms are typically not major reaction pathways. Modeling the fate of condensable low-volatility organic gases (LVOCs) formed in an OFR suggests that LVOC fate is dependent on particle condensational sink. E.g., for remote pine forest field measurements with OH$_(exp)<1 week, 20-80% of produced LVOCs were predicted to condense onto aerosols with the remainder lost to OFR or sampling line walls. A correction is needed to relate OFR sampling to the atmosphere, where condensation onto aerosols is the dominant LVOC fate. At high OH$_(exp) (>20 days), LVOCs are predicted to be oxidized faster than they can condense, forming volatile fragmentation products, so changes to preexisting OA should be predominantly a result of heterogeneous oxidation. SOA yields specific to OFR oxidation were investigated using standard addition of individual VOCs into ambient air within an OFR. SOA yields in the OFR were consistent with chamber yields. In the context of these model and experimental results, we present OFR field measurements suggesting that typically unmeasured S/IVOCs play a significant and dynamic role in ambient SOA formation.