An observationally constrained evaluation of the oxidative capacity in the tropical western Pacific troposphere

Julie M. Nicely, Daniel C. Anderson, Timothy P. Canty, Ross J. Salawitch, Glenn M. Wolfe, Eric C. Apel, Steve R. Arnold, Elliot L. Atlas, Nicola J. Blake, James F. Bresch, Teresa L. Campos, Russell R. Dickerson, Bryan Duncan, Louisa K. Emmons, Mathew J. Evans, Rafael P. Fernandez, Johannes Flemming, Samuel R. Hall, Thomas F. Hanisco, Shawn B. HonomichlRebecca S. Hornbrook, Vincent Huijnen, Lisa Kaser, Douglas E. Kinnison, Jean Francois Lamarque, Jingqiu Mao, Sarah A. Monks, Denise D. Montzka, Laura L. Pan, Daniel D. Riemer, Alfonso Saiz-Lopez, Stephen D. Steenrod, Meghan H. Stell, Simone Tilmes, Solene Turquety, Kirk Ullmann, Andrew J. Weinheimer

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


Hydroxyl radical (OH) is the main daytime oxidant in the troposphere and determines the atmospheric lifetimes of many compounds. We use aircraft measurements of O3, H2O, NO, and other species from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, which occurred in the tropical western Pacific (TWP) during January-February 2014, to constrain a photochemical box model and estimate concentrations of OH throughout the troposphere. We find that tropospheric column OH (OHCOL) inferred from CONTRAST observations is 12 to 40% higher than found in chemical transport models (CTMs), including CAM-chem-SD run with 2014 meteorology as well as eight models that participated in POLMIP (2008 meteorology). Part of this discrepancy is due to a clear-sky sampling bias that affects CONTRAST observations; accounting for this bias and also for a small difference in chemical mechanism results in our empirically based value of OHCOL being 0 to 20% larger than found within global models. While these global models simulate observed O3 reasonably well, they underestimate NOx (NO +NO2) by a factor of 2, resulting in OHCOL ~30% lower than box model simulations constrained by observed NO. Underestimations by CTMs of observed CH3CHO throughout the troposphere and of HCHO in the upper troposphere further contribute to differences between our constrained estimates of OH and those calculated by CTMs. Finally, our calculations do not support the prior suggestion of the existence of a tropospheric OH minimum in the TWP, because during January-February 2014 observed levels of O3 and NO were considerably larger than previously reported values in the TWP.

Original languageEnglish (US)
Pages (from-to)7461-7488
Number of pages28
JournalJournal of Geophysical Research
Issue number12
StatePublished - 2016

ASJC Scopus subject areas

  • Geophysics
  • Oceanography
  • Forestry
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Space and Planetary Science
  • Earth and Planetary Sciences (miscellaneous)
  • Palaeontology


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