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

  09 Jul 2020

09 Jul 2020

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This preprint is currently under review for the journal ACP.

Inverse modelling of carbonyl sulfide: implementation, evaluation and implications for the global budget

Jin Ma1, Linda M. J. Kooijmans2, Ara Cho2, Stephen A. Montzka3, Norbert Glatthor4, John R. Worden5, Le Kuai5, Elliot L. Atlas6, and Maarten C. Krol1,2 Jin Ma et al.
  • 1Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, the Netherlands
  • 2Meteorology and Air Quality, Wageningen University & Research, Wageningen, the Netherlands
  • 3National Oceanic and Atmospheric Administration (NOAA), Boulder, CO, USA
  • 4Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 5Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 6Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, USA

Abstract. Carbonyl sulfide (COS) has the potential to be used as a climate diagnostic due to its close coupling to the biospheric uptake of CO2 and its role in the formation of stratospheric aerosol. The current understanding of the COS budget, however, lacks COS sources, which have previously been allocated to the tropical ocean. This paper presents a first attempt of global inverse modelling of COS within the 4-Dimensional variational data-assimilation system of the TM5 chemistry transport model (TM5-4DVAR) and a comparison of the results with independent COS observations. We focus on the global COS budget, including COS production from its precursors carbon disulfide (CS2) and dimethyl sulfide (DMS). To this end, we implemented COS uptake by soil and vegetation from an updated biosphere model (SiB4), and new inventories for anthropogenic and biomass burning emissions. The model framework is capable of closing the COS budget by optimizing for missing emissions using NOAA observations in the period 2000–2012. The addition of 432 Gg S a−1 COS is required to obtain a good fit with NOAA observations. This missing source shows little year-to-year variations, but considerable seasonal variations. We found that the missing sources are likely located in the tropical regions, and an overestimated biospheric sink in the tropics cannot be ruled out. Moreover, high latitudes in the Northern Hemisphere require extra COS uptake or reduced emissions. HIPPO aircraft observations, NOAA airborne profiles from an ongoing monitoring program, and several satellite data sources are used to evaluate the optimized model results. This evaluation indicates that COS in the free troposphere remains underestimated after optimization. Assimilation of HIPPO observations slightly improves this model bias, which implies that additional observations are urgently required to constrain sources and sinks of COS. We finally find that the biosphere flux dependency on surface COS mixing ratio may substantially lower the fluxes of the SiB4 biosphere model over strong uptake regions. In planned further studies we will implement this biosphere dependency, and additionally assimilate satellite data with the aim to better separate the role of the oceans and the biosphere in the global COS budget.

Jin Ma et al.

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Jin Ma et al.


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Short summary
Carbonyl sulfide is an important trace gas in the atmosphere and useful to estimate gross primary productivity in ecosystem, but its sources and sinks remain highly uncertain. Therefore, we applied inverse model system TM5-4DVAR to better constrain the global budget. Our finding is in line with earlier studies, pointing to missing sources in tropics and more uptake in high latitudes. We also stress on the necessity of more ground-based observations and satellite data assimilation in future.
Carbonyl sulfide is an important trace gas in the atmosphere and useful to estimate gross...