Observed NO/NO_2 Ratios in the Upper Troposphere Imply Errors in NO-NO_2-O_3 Cycling Kinetics or an Unaccounted NO_x Reservoir

Creators: Silvern, R. F.; Jacob, D. J.; Travis, K. R.; Sherwen, T.; Evans, M. J.; Cohen, R. C.; Laughner, J. L.; Hall, S. R.; Ullmann, K.; Crounse, J. D.; Wennberg, P. O.; Peischl, J.; Pollack, I. B.

Abstract

Observations from the SEAC^4RS aircraft campaign over the southeast United States in August–September 2013 show NO/NO_2 concentration ratios in the upper troposphere that are approximately half of photochemical equilibrium values computed from Jet Propulsion Laboratory (JPL) kinetic data. One possible explanation is the presence of labile NO_x reservoir species, presumably organic, decomposing thermally to NO_2 in the instrument. The NO_2 instrument corrects for this artifact from known labile HNO_4 and CH_3O_2NO_2 NO_x reservoirs. To bridge the gap between measured and simulated NO_2, additional unaccounted labile NO_x reservoir species would have to be present at a mean concentration of ~40 ppt for the SEAC^4RS conditions (compared with 197 ppt for NOx). An alternative explanation is error in the low‐temperature rate constant for the NO + O_3 reaction (30% 1‐σ uncertainty in JPL at 240 K) and/or in the spectroscopic data for NO_2 photolysis (20% 1‐σ uncertainty). Resolving this discrepancy is important for understanding global budgets of tropospheric oxidants and for interpreting satellite observations of tropospheric NO_2 columns.

Additional Information

© 2018 The Authors. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made. Received 27 OCT 2017; Accepted 20 APR 2018; Accepted article online 30 APR 2018; Published online 12 MAY 2018. We thank Tom Ryerson for his measurements of NO and O_3 from the NOAA NO_yO_3 instrument. This work was supported by the NASA Earth Science Division and USEPA grant 83587201. Its contents are solely the responsibility of the grantee and do not necessarily represent the official views of the USEPA. Further, USEPA does not endorse the purchase of any commercial products or services mentioned in the publication. SEAC^4RS airborne measurements are available from the NASA LaRC Airborne Science Data for Atmospheric Composition (http://www‐air.larc.nasa.gov/cgi‐bin/ArcView/seac4rs). OMI NO_2 observations are available from the NASA Goddard Earth Sciences Data and Information Services Center (https://aura.gesdisc.eosdis.nasa.gov/data/Aura_OMI_Level2/OMNO2.003/).

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