AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Controlled NO and NO2 Production via O(1D)-N2O Reactions for Use in Oxidation Flow Reactor Studies of SOA Formation Pathways
ANDREW LAMBE, Paola Massoli, John B. Nowak, Manjula Canagaratna, Conner Daube, Timothy Onasch, Lindsay Renbaum-Wolff, Gabriel Isaacman-VanWertz, Jesse Kroll, John Jayne, Paul Davidovits, Charles Kolb, Douglas Worsnop, William Brune, Aerodyne Research, Inc.
Abstract Number: 208 Working Group: Instrumentation and Methods
Abstract Oxidation flow reactors that use low-pressure mercury lamps to produce hydroxyl (OH) radicals are an emerging technique for studying the oxidative aging of organic aerosols. In these flow reactors, ozone is photolyzed at λ = 254 nm to produce O(1D) radicals, which react with H2O to produce OH. However, the need to use parts-per-million levels of ozone hinders the ability of flow reactors to simulate NOx-dependent SOA formation pathways. Simple addition of NO and/or NO2 to oxidation flow reactors results in fast conversion of NOx to nitric acid, making it difficult to sustain NOx levels that are sufficient to compete with hydroperoxy (HO2) radicals as a sink for organic peroxy (RO2) radicals. Here, we present a new method that is well suited to the characterization of NOx-dependent SOA formation pathways in oxidation flow reactors. NO and NO2 are produced via the reaction O(1D)+N2O→2NO, followed by the reaction NO+O3→NO2+O2. Laboratory measurements coupled with photochemical box model simulations suggest that O(1D)+N2O reactions can be used to systematically vary the relative branching ratios of RO2 + NO and RO2 + HO2 reactions over a range of conditions relevant to atmospheric SOA formation. We demonstrate proof of concept using high-resolution time-of-flight chemical ionization mass spectrometer measurements to detect gas-phase oxidation products of isoprene and α-pinene that have been observed in recent NOx-influenced field studies and laboratory chamber experiments. We also detect condensed-phase organonitrate oxidation products of α-pinene that are formed in the presence of added NOx using a high-resolution time-of-flight aerosol mass spectrometer.