EGU2020-9908
https://doi.org/10.5194/egusphere-egu2020-9908
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

The potential of satellite data to calculate the global OH distribution using simplified steady state approximations

Matilda Pimlott1, Martyn Chipperfield1,2, Richard Pope1,2, Brian Kerridge3,4, and Richard Siddans3,4
Matilda Pimlott et al.
  • 1University of Leeds, School of Earth and Environment, Leeds, United Kingdom
  • 2National Centre for Earth Observation, University of Leeds, Leeds, United Kingdom
  • 3Remote Sensing Group, STFC Rutherford Appleton Laboratory, Chilton, United Kingdom
  • 4National Centre for Earth Observation, STFC Rutherford Appleton Laboratory, Chilton, United Kingdom

The hydroxyl radical (OH) is one of the most important species in atmospheric chemistry. It plays a dominant role in the oxidation of many other species in the troposphere, such as anthropogenic pollutants. Direct in-situ and satellite measurements of OH are scarce due to its short lifetime (around 1 second) and low abundance. Other indirect methods of inferring global mean OH have been established, such as using methyl chloroform as a tracer. However because of its recent phase out there is a demand for another method of calculating the global OH abundance. It is therefore useful to explore indirect methods for calculating OH. In particular, global satellite data can provide a means for estimating mean OH within large atmospheric regions. An improved understanding of the global distribution of OH will allow a better understanding of atmospheric chemistry, especially the distributions of anthropogenic pollutants.  

Due to the short lifetime of OH, a steady-state approximation can be used to model its concentration. This allows the OH distribution to be calculated using a simple equation and the accuracy of the estimate depends on the number of source/sink terms which can be included in the equation. In this work, a steady state approximation has been applied to the global OH budget as defined in the TOMCAT 3-D model. The full steady-state equation (based on all reactions in the model) has been simplified in various ways to include only the major sources and sinks of OH that can be observed directly by satellite, such as carbon monoxide (CO), methane (CH4), water vapour (H2O) and ozone (O3). 

Recent satellite observations of these species is then applied to the steady-state approximation to derive an estimate of the global OH distribution. We use the 3-D model to determine where the simplified steady-state approximation is likely to be most valid. The overall potential of this method to calculate an accurate OH distribution, bearing in mind satellite observation errors, is discussed. 

How to cite: Pimlott, M., Chipperfield, M., Pope, R., Kerridge, B., and Siddans, R.: The potential of satellite data to calculate the global OH distribution using simplified steady state approximations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9908, https://doi.org/10.5194/egusphere-egu2020-9908, 2020.