Open AccessResolving the Model‐Observation Discrepancy in the Mesospheric and Stratospheric HO x Chemistry
Author(s) -
Li KingFai,
Zhang Qiong,
Wang Shuhui,
Sander Stanley P.,
Yung Yuk L.
Publication year - 2017
Publication title -
earth and space science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.843
H-Index - 23
ISSN - 2333-5084
DOI - 10.1002/2017ea000283
Subject(s) - microwave limb sounder , kinetic energy , absorption (acoustics) , reaction rate , radiative transfer , analytical chemistry (journal) , atmospheric chemistry , reaction rate constant , absorption cross section , chemistry , physics , stratosphere , atmospheric sciences , kinetics , meteorology , ozone , optics , cross section (physics) , catalysis , environmental chemistry , biochemistry , quantum mechanics
We examine the middle atmospheric odd‐hydrogen (HO x ) chemistry by comparing the Aura Microwave Limb Sounder (MLS) OH and HO 2 measurements with a photochemical model simulation. The model underestimates mesospheric OH and HO 2 concentrations if the standard chemical kinetic rates are used, whether the model H 2 O and O 3 are constrained with observations or not. To resolve the discrepancies, we adjust the kinetic rate coefficients of three key reactions (O + OH → O 2 + H, OH + HO 2 → H 2 O + O 2 , and H + O 2 + M → HO 2 + M) and the O 2 photo absorption cross section at Lyman α (121.57 nm) using the Bayesian optimal estimation. A much better model‐observation agreement can be achieved if the kinetic rate coefficients for H + O 2 + M → HO 2 + M is increased by 134–310%, and the O 2 photo absorption cross section at Lyman α is reduced by 33–54%, while the kinetic rate coefficients for O + OH → O 2 + H and OH + HO 2 → H 2 O + O 2 remain consistent with the current laboratory values. The kinetic rate coefficient for H + O 2 + M → HO 2 + M requires a very large adjustment beyond the uncertainty limits recommended in the NASA Data Evaluation, suggesting the need for future laboratory measurements. An alternative explanation is that the radiative association reaction, H + O 2 → HO 2 + h ν, plays a significant role, which has never been measured. Our results demonstrate that high‐quality satellite observations can be used to constrain photochemical parameters and help improve our understanding of atmospheric chemistry.