EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Constraints on OH in a global 3D inversion of methyl chloroform

Stijn Naus1, Stephen Montzka2, Prabir Patra3, and Maarten Krol1,4
Stijn Naus et al.
  • 1Wageningen University and Research, Environmental Sciences, Meteorology and Air Quality, Wageningen, Netherlands (
  • 2NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, CO, USA
  • 3Research Institute for Global Change, JAMSTEC, Yokohama, Japan.
  • 4Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, the Netherlands

The hydroxyl radical (OH) is the primary atmospheric oxidant. In this role, OH is involved in the removal of a wide variety of atmospheric pollutants and greenhouse gases. Despite the central role of OH in atmospheric chemistry, important metrics such as interannual variability and trends in OH on large spatial scales remain poorly constrained. This is mainly due to its low abundance and short lifetime of seconds.

Over the past decades, the anthropogenically emitted methyl chloroform (MCF) has been uniquely qualified as a tracer to indirectly constrain OH on large spatio-temporal scales. However, recent box model studies have shown that OH, as estimated from MCF observations, is still very uncertain 1,2,3. This translates for example to large uncertainties in global methane (CH4) emissions, even if changes in the global CH4 burden are well-defined. Box model studies however, do not fully capitalize on the MCF measurement network and the gradients therein. Moreover, they may introduce biases due to incorrect or incomplete representation of atmospheric transport.

Here, we present results from a 4DVAR inversion of MCF over the 1998-2018 period, performed in the 3D chemistry-transport model TM5. Starting from typical OH priors, we find adjustments in the OH spatio-temporal distribution that bring the simulated MCF mole fractions closer to observations. Large uncertainties in this improved estimate remain, but we find that no large interannual variability (>2%) and no significant trend in global mean OH are needed to match MCF observations. We do find significant adjustments in the latitudinal gradients of OH (e.g. an increase in tropical OH).

Rigby, M., et al. PNAS (2017), 114.21: 5373-5377

2 Turner, A.J., et al. PNAS (2017), 114.21: 5367-5372

3 Naus, S et al. ACP (2019), 19.1: 407-424

How to cite: Naus, S., Montzka, S., Patra, P., and Krol, M.: Constraints on OH in a global 3D inversion of methyl chloroform, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18458,, 2020


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displays version 2 – uploaded on 01 May 2020, no comments
I hadn't included the proper acknowledgements.
displays version 1 – uploaded on 01 May 2020, no comments