Preprints
https://doi.org/10.5194/acp-2021-238
https://doi.org/10.5194/acp-2021-238

  28 Apr 2021

28 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

Evaluation of SO2, SO42− and an updated SO2 dry deposition parameterization in UKESM1

Catherine Hardacre1, Jane P. Mulcahy1, Richard Pope2,3, Colin G. Jones3, Steven R. Rumbold3, Can Li4,5, and Steven T. Turnock1,6 Catherine Hardacre et al.
  • 1Met Office, Exeter, EX1 3PB, UK
  • 2School Earth and Environment, University of Leeds, Leeds, UK
  • 3National Centre for Atmospheric Science, University of Leeds, Leeds, UK
  • 4NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 5Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, USA
  • 6University of Leeds Met Office Strategic (LUMOS) Research Group, School of Earth and Environment, University of Leeds, UK

Abstract. In this study we evaluate simulated surface SO2 and sulphate (SO42−) concentrations from the United Kingdom Earth System Model (UKESM1) against observations from ground based measurement networks in the USA and Europe for the period 1987 to 2014. We find that UKESM1 captures the historical trend for decreasing concentrations of atmospheric SO2 and SO42− in both Europe and the USA over the period 1987 to 2014. However, in the polluted regions of the eastern USA and Europe, UKESM1 over-predicts surface SO2 concentrations by a factor of 3, while under-predicting surface SO42− concentrations by 25–35 %. In the cleaner western USA, the model over-predicts both surface SO2 and SO42− concentrations by a factor of 12 and 1.5 respectively. We find that UKESM1’s bias in surface SO2 and SO42− concentrations is variable according to region and season. We also evaluate UKESM1 against total column SO2 from the Ozone Monitoring Instrument (OMI) using an updated data product. This comparison provides information about the model’s global performance, finding that UKESM1 over predicts total column SO2 over much of the globe, including the large source regions of India, China, the USA and Europe as well as over outflow regions. Finally, we assess the impact of a more realistic treatment of the model’s SO2 dry deposition parameterization. This change increases SO2 dry deposition to the land and ocean surfaces, thus reducing the atmospheric loading of SO2 and SO42− . In comparison with the ground-based and satellite observations, we find that the modified parameterization reduces the model’s over prediction of surface SO2 concentrations and total column SO2. Relative to the ground-based observations the simulated surface SO42− concentrations are also reduced, while the simulated SO2 dry deposition fluxes increase.

Catherine Hardacre et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Note bias in emissions data over western USA', Steven Smith, 13 May 2021
  • RC1: 'Comment on acp-2021-238', Anonymous Referee #2, 12 Jun 2021
  • RC2: 'Comment on acp-2021-238', Anonymous Referee #1, 22 Jun 2021

Catherine Hardacre et al.

Catherine Hardacre et al.

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Short summary
We investigate UKESM1's ability to represent the sulphur (S) cycle in the recent historical period. The S cycle is a key driver of historical radiative forcing. Earth system models such as UKESM1 should represent the S cycle well so that we can have confidence in their projections of future climate. We compare UKESM1 to observations of sulphur compounds finding that the model generally performs well. We also identify areas for UKESM1’s development, focussing on how SO2 is removed from the air.
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