Controlled nitric oxide production via O(1D)+N2O reactions for use in oxidation flow reactor studies
Andrew Lambe1,2, Paola Massoli1, Xuan Zhang1, Manjula Canagaratna1, John Nowak1,*, Chao Yan3, Wei Nie4,3, Timothy Onasch1,2, John Jayne1, Charles Kolb1, Paul Davidovits2, Douglas Worsnop1,3, and William Brune51Aerodyne Research, Inc., Billerica, Massachusetts, United States 2Chemistry Department, Boston College, Chestnut Hill, Massachusetts, United States 3Physics Department, University of Helsinki, Helsinki, Finland 4Joint International Research Laboratory of Atmospheric and Earth System Sciences, School of Atmospheric Sciences, Nanjing University, Nanjing, China 5Department of Meteorology and Atmospheric Sciences, The Pennsylvania State University, University Park, Pennsylvania, United States *Current address: Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, Virgina, United State
Received: 30 Nov 2016 – Accepted for review: 05 Jan 2017 – Discussion started: 06 Jan 2017
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. Here, ozone (O3) is photolyzed at 254 nm to produce O(1D) radicals, which react with water vapor to produce OH. However, the need to use parts-per-million levels of O3 hinders the ability of oxidation ﬂow reactors to simulate NOx-dependent SOA formation pathways. Simple addition of nitric oxide (NO) results in fast conversion of NOx (NO + NO2) to nitric acid (HNO3), making it impossible to sustain NO at levels that are sufﬁcient to compete with hydroperoxy (HO2) radicals as a sink for organic peroxy (RO2) radicals. We developed 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 model simulations suggest that O(1D) + N2O reactions can be used to systematically vary the relative branching ratio of RO2 + NO reactions relative to RO2 + HO2 and/or RO2 + RO2 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 (HR-ToF-CIMS) measurements with nitrate (NO3−) reagent ion to detect gas-phase oxidation products of isoprene and α-pinene previously observed in NOx-inﬂuenced environments and in laboratory chamber experiments.
Lambe, A., Massoli, P., Zhang, X., Canagaratna, M., Nowak, J., Yan, C., Nie, W., Onasch, T., Jayne, J., Kolb, C., Davidovits, P., Worsnop, D., and Brune, W.: Controlled nitric oxide production via O(1D)+N2O reactions for use in oxidation flow reactor studies, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-394, in review, 2017.