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

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.

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Author Nicely, Julie
Anderson, Daniel
Canty, Timothy
Salawitch, Ross
Wolfe, Glenn
Apel, Eric
Arnold, Steve
Atlas, Elliot
Blake, Nicola
Bresch, James
Campos, Teresa
Dickerson, Russell
Duncan, Bryan
Emmons, Louisa
Evans, Mathew
Fernandez, Rafael
Fleming, Johannes
Hall, Samuel
Hanisco, Thomas
Honomichl, Shawn
Hornbrook, Rebecca
Huijnen, Vincent
Kaser, Lisa
Kinnison, Douglas
Lamarque, Jean-Francois
Mao, Jingqiu
Monks, Sarah
Montzka, Denise
Pan, Laura
Riemer, Daniel
Saiz-Lopez, Alfonso
Steenrod, Stephen
Stell, Meghan
Tilmes, Simone
Turquety, Solene
Ullmann, Kirk
Weinheimer, Andrew
Publisher UCAR/NCAR - Library
Publication Date 2016-06-27T00:00:00
Digital Object Identifier (DOI) Not Assigned
Alternate Identifier N/A
Resource Version N/A
Topic Category geoscientificInformation
Progress N/A
Metadata Date 2023-08-18T19:02:34.995394
Metadata Record Identifier edu.ucar.opensky::articles:18612
Metadata Language eng; USA
Suggested Citation Nicely, Julie, Anderson, Daniel, Canty, Timothy, Salawitch, Ross, Wolfe, Glenn, Apel, Eric, Arnold, Steve, Atlas, Elliot, Blake, Nicola, Bresch, James, Campos, Teresa, Dickerson, Russell, Duncan, Bryan, Emmons, Louisa, Evans, Mathew, Fernandez, Rafael, Fleming, Johannes, Hall, Samuel, Hanisco, Thomas, Honomichl, Shawn, Hornbrook, Rebecca, Huijnen, Vincent, Kaser, Lisa, Kinnison, Douglas, Lamarque, Jean-Francois, Mao, Jingqiu, Monks, Sarah, Montzka, Denise, Pan, Laura, Riemer, Daniel, Saiz-Lopez, Alfonso, Steenrod, Stephen, Stell, Meghan, Tilmes, Simone, Turquety, Solene, Ullmann, Kirk, Weinheimer, Andrew. (2016). An observationally constrained evaluation of the oxidative capacity in the tropical western Pacific troposphere. UCAR/NCAR - Library. http://n2t.net/ark:/85065/d7gb25pq. Accessed 19 July 2025.

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