09 Jan 2023
09 Jan 2023
Status: this preprint is currently under review for the journal ACP.

Exploring the Drivers of Tropospheric Hydroxyl Radical Trends in the GFDL AM4.1 Atmospheric Chemistry-Climate Model

Glen Chua1,2, Vaishali Naik2, and Larry Wayne Horowitz2 Glen Chua et al.
  • 1Princeton University, Program in Atmospheric and Oceanic Science
  • 2NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA

Abstract. We explore the sensitivity of modelled tropospheric hydroxyl (OH) concentration trends to meteorology and near-term climate forcers (NTCFs), namely methane (CH4); nitrogen oxides (NOx = NO2 + NO); carbon monoxide (CO); non-methane volatile organic compounds (NMVOCs); and ozone-depleting substances (ODS) using the Geophysical Fluid Dynamics Laboratory’s (GFDL) atmospheric chemistry-climate model, Atmospheric Model version 4.1 (AM4.1) driven by emissions inventories developed for the Sixth Coupled Model Intercomparison Project (CMIP6) and forced by observed sea surface temperatures and sea ice prepared in support of the CMIP6 Atmospheric Model Intercomparison Project (AMIP) simulations. We find that the modelled tropospheric airmass-weighted mean [OH] has increased by ~5 % globally from 1980 to 2014. We find that NOx emissions and CH4 concentrations dominate the modelled global trend, while CO emissions and meteorology were also important in driving regional trends. Modelled tropospheric NO2 column trends are largely consistent with those retrieved from the Ozone Monitoring Instrument (OMI) satellite, but simulated CO column trends generally overestimate those retrieved from the Measurements of Pollution in The Troposphere (MOPITT) satellite, possibly reflecting biases in input anthropogenic emission inventories, especially over China and South Asia.

Glen Chua et al.

Status: open (until 20 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2023-9', Anonymous Referee #1, 28 Jan 2023 reply
  • RC2: 'Comment on acp-2023-9', Anonymous Referee #2, 30 Jan 2023 reply

Glen Chua et al.

Glen Chua et al.


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Short summary
The hydroxyl radical (OH) is an atmospheric 'detergent', removing air pollutants and greenhouse gases like methane from the atmosphere. Thus, understanding how it is changing and responding to its various drivers is important for air quality and climate. We found that OH has increased by about 5 % globally from 1980 to 2014 in our model, mostly driven by increasing nitrogen oxide (NOx) emissions. This suggests potential climate tradeoffs from air quality policies solely targeting NOx emissions.