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Discussion papers
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 03 Jan 2020

Submitted as: research article | 03 Jan 2020

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Constraining remote oxidation capacity with ATom observations

Katherine R. Travis1,a, Colette L. Heald1,2, Hannah M. Allen3, Eric C. Apel4, Stephen R. Arnold5, Donald R. Blake6, William H. Brune7, Xin Chen8, Roisin Commane9, John D. Crounse10, Bruce C. Daube11, Glenn S. Diskin12, James W. Elkins13, Mathew J. Evans14,15, Samuel R. Hall4, Eric J. Hintsa13,16, Rebecca S. Hornbrook4, Prasad S. Kasibhatla17, Michelle J. Kim10,18, Gan Luo19, Kathryn McKain20, Dylan B. Millet8, Fred L. Moore13,16, Jeffrey Peischl16,20, Thomas B. Ryerson20, Tomas Sherwen14,15, Alexander B. Thames7, Kirk Ullmann4, Xuan Wang11,21, Paul O. Wennberg3,18, Glenn M. Wolfe22, and Fangqun Yu19 Katherine R. Travis et al.
  • 1Department of Civil and Environmental Engineering, Massachusetts Instituteof Technology, Cambridge, MA, USA
  • 2Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
  • 3Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
  • 4Atmospheric Chemistry Observations & Modeling Laboratory, National Center for Atmospheric Research, Boulder, Colorado, USA
  • 5Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK
  • 6Department of Chemistry, University of California Irvine, Irvine, CA, USA
  • 7Department of Meteorology, Pennsylvania State University, University Park, PA, USA
  • 8University of Minnesota, Department of Soil, Water and Climate, St. Paul, Minnesota, USA
  • 9Dept. of Earth & Environmental Sciences of Lamont-Doherty Earth Observatory and Columbia University, Palisades, NY, USA
  • 10Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 11Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 12NASA Langley Research Center, Hampton, Virginia, USA
  • 13Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 14Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry, University of York, York, UK
  • 15National Centre for Atmospheric Science (NCAS), University of York, York, UK
  • 16Cooperative Institute for Research in Environmental Science, University of Colorado, USA
  • 17Nicholas School of the Environment, Duke University, Durham, NC, USA
  • 18Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA
  • 19Atmospheric Sciences Research Center, University of Albany, Albany, New York, USA
  • 20Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 21School of Energy and Environment, City University of Hong Kong, Hong Kong, China
  • 22Atmospheric Chemistry and Dynamics Laboratory, NASA GoddardSpace Flight Center, Greenbelt, MD, USA
  • anow at: NASA Langley Research Center, Hampton, Virginia, USA

Abstract. The global oxidation capacity, defined as the tropospheric mean concentration of the hydroxyl radical (OH), controls the lifetime of reactive trace gases in the atmosphere such as methane and carbon monoxide (CO). Models tend to underestimate the methane lifetime and CO concentrations throughout the troposphere, which is consistent with excessive OH. Approximately half the oxidation of methane and non-methane volatile organic compounds (VOCs) is thought to occur over the oceans where oxidant chemistry has received little validation due to a lack of observational constraints. We use observations from the first two deployments of the NASA ATom aircraft campaign during July–August 2016 and January–February 2017 to evaluate the oxidation capacity over the remote oceans and its representation in the GEOS-Chem chemical transport model. The model successfully simulates the magnitude and vertical profile of remote OH within the measurement uncertainties. Comparisons against the drivers of OH production (water vapor, ozone, and NOy concentrations, ozone photolysis frequencies) also show minimal bias with the exception of wintertime NOy, for which a model overestimate may indicate insufficient wet scavenging and/or missing loss on seasalt aerosol but large uncertainties remain that require further studies of NOy partitioning and removal in the troposphere. During the ATom-1 deployment, OH reactivity (OHR) below 3 km is significantly enhanced, and this is not captured by the sum of its measured components (cOHRobs) or by the model (cOHRmod). This enhancement could suggest missing reactive VOCs but cannot be explained by new estimates of ocean VOC sources and additional modeled reactivity in this region would be difficult to reconcile with the full suite of ATom measurement constraints. The model generally reproduces the magnitude and seasonality of cOHRobs but underestimates the contribution of oxygenated VOC, mainly acetaldehyde, which is severely underestimated throughout the troposphere despite its calculated lifetime of less than a day. Missing model acetaldehyde in previous studies was attributed to measurement uncertainties that have been largely resolved. Observations of peroxyacetic acid (PAA) provide new support for remote levels of acetaldehyde. The underestimate in modeled acetaldehyde and PAA is present throughout the year in both hemispheres and peaks during Northern Hemisphere summer. The addition of ocean VOC sources in the model increases annual surface cOHRmod by 10 % and improves model-measurement agreement for acetaldehyde particularly in winter but cannot resolve the model summertime bias. Doing so would require a 100 Tg yr−1 source of a long-lived unknown precursor throughout the year with significant additional emissions in the Northern Hemisphere summer. Improving the model bias for remote acetaldehyde and PAA is unlikely to fully resolve previously reported model global biases in OH and methane lifetime, suggesting that future work should examine the sources and sinks of OH over land.

Katherine R. Travis et al.
Interactive discussion
Status: open (until 28 Feb 2020)
Status: open (until 28 Feb 2020)
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Katherine R. Travis et al.
Data sets

Atmospheric Tomography Mission (ATom) S.C. Wofsy, S. Afshar, H.M. Allen, E.C. Apel, E.C. Asher, B. Barletta, J. Bent, H. Bian, B.C. Biggs, D.R. Blake, N. Blake, I. Bourgeois, C.A. Brock, W.H. Brune, J.W. Budney, T.P. Bui, A. Butler, P. Campuzano-Jost, C.S. Chang, M. Chin, R. Commane, G. Correa, J.D. Crounse, P. D. Cullis, B.C. Daube, D.A. Day, J.M. Dean-Day, J.E. Dibb, J.P. DiGangi, G.S. Diskin, M. Dollner, J.W. Elkins, F. Erdesz, A.M. Fiore, C.M. Flynn, K.D. Froyd, D.W. Gesler, S.R. Hall, T.F. Hanisco, R.A. Hannun, A.J. Hills, E.J. Hintsa, A. Hoffman, R.S. Hornbrook, L.G. Huey, S. Hughes, J.L. Jimenez, B.J. Johnson, J.M. Katich, R.F. Keeling, M.J. Kim, A. Kupc, L.R. Lait, J.-F. Lamarque, J. Liu, K. McKain, R.J. Mclaughlin, S. Meinardi, D.O. Miller, S.A. Montzka, F.L. Moore, E.J. Morgan, D.M. Murphy, L.T. Murray, B.A. Nault, J.A. Neuman, P.A. Newman, J.M. Nicely, X. Pan, W. Paplawsky, J. Peischl, M.J. Prather, D.J. Price, E. Ray, J.M. Reeves, M. Richardson, A.W. Rollins, K.H. Rosenlof, T.B. Ryerson, E. Scheuer, G.P. Schill, J.C. Schroder, J.P. Schwarz, J.M. St.Clair, S.D. Steenrod, B.B. Stephens, S.A. Strode, C. Sweeney, D. Tanner, A.P. Teng, A.B. Thames, C.R. Thompson, K. Ullmann, P.R. Veres, N. Vieznor, N.L. Wagner, A. Watt, R. Weber, B. Weinzierl, P.O. Wennberg, C.J. Williamson, J.C. Wilson, G.M. Wolfe, C.T. Woods, and L.H. Zeng.

Model code and software

GEOS-Chem 12.3.0

Katherine R. Travis et al.
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Publications Copernicus
Short summary
Atmospheric models overestimate the rate of removal of trace gases by the hydroxyl radical (OH). This is a concern for studies of the climate and air quality effects of human activities. Here, we evaluate the performance of a commonly used model of atmospheric chemistry against data from the Atmospheric Tomography Mission (ATom) taken over the remote oceans where models have received little validation. The model is generally successful, suggesting that biases in OH may be a concern over land.
Atmospheric models overestimate the rate of removal of trace gases by the hydroxyl radical (OH)....