Tropospheric OH and its trends: new insight into atmospheric processes and implications for methane lifetime
- 1Lancaster University (Lancaster, United Kingdom)
- 2Nanjing University of Information Science and Technology (Nanjing, China)
Abstract
The hydroxyl radical (OH) is a critical determinant of global oxidative capacity and trace gas lifetimes, but its variation remains poorly constrained. This study investigates the sensitivity of modelled tropospheric OH concentration changes to new understanding of physical and chemical processes using the FRSGC/UCI chemistry transport model. We show that simulated tropospheric O ₃ and NO ₂ agree well with satellite observations, but that annual variations in CO do not, likely due to uncertainties in biomass burning emissions in the southern hemisphere and overestimated CO trends over Asia. This discrepancy, along with the background increase in CO, may lead to an underestimation of OH increase or overestimation of OH decrease from 2000 to 2017. Changes in tropospheric OH column show substantial spatial heterogeneity, with increases in OH in high-emission regions and decreases in the tropics. Global mean OH trends are dependent on the assumed trend in emissions: with time-varying emissions there is little change in OH, while under annually invariant emissions, OH increases in response to changes in meteorological conditions. Inclusion of water vapor UV absorption, heterogeneous reactions, and updates to the OH+NO ₂ reaction rate have a smaller impact, but decrease OH levels by 3.6 %, 5.8 %, and 7.0 %, respectively, increasing CH ₄ lifetimes by 4.2 %, 5.2 %, and 8.4 %. Incorporating oceanic CH ₃ CHO emissions reduces global mean OH by up to 1.5 %, increasing the CH ₄ lifetime by up to 1.6 %. These results provide a quantitative basis for understanding the drivers of tropospheric OH variability and their implications for global methane chemistry.
Versions
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BibTeX
@article{hou2026tropospheric,
title = {{Tropospheric OH and its trends: new insight into atmospheric processes and implications for methane lifetime}},
author = {Xuewei Hou and Ryan Hossaini and Oliver Wild and Andrea Mazzeo and Richard J. Pope and Ye Wang and Siyuan Wang and Yuanhong Zhao and James Lee and Bin Zhu and Tianliang Zhao and Alok K. Pandey},
journal = {Atmospheric Chemistry and Physics},
year = {2026},
month = oct,
doi = {10.5194/acp-26-13767-2026},
url = {https://acp.copernicus.org/articles/26/13767/2026/},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Tropospheric OH and its trends: new insight into atmospheric processes and implications for methane lifetime
AU - Xuewei Hou
AU - Ryan Hossaini
AU - Oliver Wild
AU - Andrea Mazzeo
AU - Richard J. Pope
AU - Ye Wang
AU - Siyuan Wang
AU - Yuanhong Zhao
AU - James Lee
AU - Bin Zhu
AU - Tianliang Zhao
AU - Alok K. Pandey
PY - 2026
DA - 2026/10/01
JO - Atmospheric Chemistry and Physics
DO - 10.5194/acp-26-13767-2026
UR - https://acp.copernicus.org/articles/26/13767/2026/
AB - The hydroxyl radical (OH) is a critical determinant of global oxidative capacity and trace gas lifetimes, but its variation remains poorly constrained. This study investigates the sensitivity of modelled tropospheric OH concentration changes to new understanding of physical and chemical processes using the FRSGC/UCI chemistry transport model. We show that simulated tropospheric O ₃ and NO ₂ agree well with satellite observations, but that annual variations in CO do not, likely due to uncertainties in biomass burning emissions in the southern hemisphere and overestimated CO trends over Asia. This discrepancy, along with the background increase in CO, may lead to an underestimation of OH increase or overestimation of OH decrease from 2000 to 2017. Changes in tropospheric OH column show substantial spatial heterogeneity, with increases in OH in high-emission regions and decreases in the tropics. Global mean OH trends are dependent on the assumed trend in emissions: with time-varying emissions there is little change in OH, while under annually invariant emissions, OH increases in response to changes in meteorological conditions. Inclusion of water vapor UV absorption, heterogeneous reactions, and updates to the OH+NO ₂ reaction rate have a smaller impact, but decrease OH levels by 3.6 %, 5.8 %, and 7.0 %, respectively, increasing CH ₄ lifetimes by 4.2 %, 5.2 %, and 8.4 %. Incorporating oceanic CH ₃ CHO emissions reduces global mean OH by up to 1.5 %, increasing the CH ₄ lifetime by up to 1.6 %. These results provide a quantitative basis for understanding the drivers of tropospheric OH variability and their implications for global methane chemistry.
SN - 1680-7324
ER -