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An observationally constrained evaluation of the oxidative capacity in the tropical western Pacific troposphere
Author(s) -
Nicely Julie M.,
Anderson Daniel C.,
Canty Timothy P.,
Salawitch Ross J.,
Wolfe Glenn M.,
Apel Eric C.,
Arnold Steve R.,
Atlas Elliot L.,
Blake Nicola J.,
Bresch James F.,
Campos Teresa L.,
Dickerson Russell R.,
Duncan Bryan,
Emmons Louisa K.,
Evans Mathew J.,
Fernandez Rafael P.,
Flemming Johannes,
Hall Samuel R.,
Hanisco Thomas F.,
Honomichl Shawn B.,
Hornbrook Rebecca S.,
Huijnen Vincent,
Kaser Lisa,
Kinnison Douglas E.,
Lamarque JeanFrancois,
Mao Jingqiu,
Monks Sarah A.,
Montzka Denise D.,
Pan Laura L.,
Riemer Daniel D.,
SaizLopez Alfonso,
Steenrod Stephen D.,
Stell Meghan H.,
Tilmes Simone,
Turquety Solene,
Ullmann Kirk,
Weinheimer Andrew J.
Publication year - 2016
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd025067
Subject(s) - troposphere , atmospheric sciences , chemical transport model , environmental science , climatology , box model , atmospheric chemistry , daytime , tropics , sky , photochemistry , meteorology , ozone , chemistry , physics , geology , fishery , biology
Hydroxyl radical (OH) is the main daytime oxidant in the troposphere and determines the atmospheric lifetimes of many compounds. We use aircraft measurements of O 3 , H 2 O, 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 (OH COL ) 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 OH COL being 0 to 20% larger than found within global models. While these global models simulate observed O 3 reasonably well, they underestimate NO x (NO + NO 2 ) by a factor of 2, resulting in OH COL ~30% lower than box model simulations constrained by observed NO. Underestimations by CTMs of observed CH 3 CHO 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 O 3 and NO were considerably larger than previously reported values in the TWP.