Intercomparison of Atmospheric Carbonyl Sulfide (TransCom‐COS; Part One): Evaluating the Impact of Transport and Emissions on Tropospheric Variability Using Ground‐Based and Aircraft Data

Abstract

We present a comparison of atmospheric transport model simulations for carbonyl sulfide (COS), within the framework of the ongoing atmospheric tracer transport model intercomparison project "TransCom". Seven atmospheric transport models participated in the inter-comparison experiment and provided simulations of COS mixing ratios in the troposphere over a 9-year period (2010-2018), using prescribed state-of-the-art surface fluxes for various components of the atmospheric COS budget: biospheric sink, oceanic source, sources from fire and industry. Since the biosphere is the largest sink of COS, we tested sink estimates produced by two different biosphere models. The main goals of TransCom-COS are (a) to investigate the impact of the transport uncertainty and emission distribution in simulating the spatio-temporal variability of COS mixing ratios in the troposphere, and (b) to assess the sensitivity of simulated tropospheric COS mixing ratios to the seasonal and diurnal variability of the COS biosphere fluxes. To this end, a control case with state-of-the-art seasonal fluxes of COS was constructed. Models were run with the same fluxes and without chemistry to isolate transport differences. Further, two COS flux scenarios were compared: one using a biosphere flux with a monthly time resolution and the other using a biosphere flux with a three-hourly time resolution. In addition, we investigated the sensitivity of the simulated concentrations to different biosphere fluxes and to indirect oceanic emissions through dimethylsulfide (DMS) and carbon disulfide (CS 2 ). The modelled COS mixing ratios were assessed against in-situ observations from surface stations and aircraft.

Intercomparison of Atmospheric Carbonyl Sulfide (TransCom‐COS): 2. Evaluation of Optimized Fluxes Using Ground‐Based and Aircraft Observations

“…The ATMs then simulated the atmospheric COS concentration (3D) following the transport of COS surface fluxes. For a comparison to the results with the optimized fluxes, we also present results from the control scenario described in part I (Remaud et al., 2023a). Relying on the linearity of the atmospheric transport, each flux of the control scenario was transported separately by all participating models, after which the contributions were added.…”

“…TM3 did not provide 3D model output and is assumed to be in the strong mixing group, because the vertical transport parameterization is similar to TM5. The impact of the vertical mixing on the seasonal cycle is known as the seasonal rectifier effect (Denning et al, 1995) and is shown in the case of COS on Figure 4 in Remaud et al (2023a).…”

“…Also, both inversions reproduced independent data from the HIAPER Pole‐To‐Pole Observations (HIPPO) campaigns to some extent, but pointed out the importance of atmospheric transport to infer the surface fluxes and the need for further analysis of the impact of transport uncertainties on the COS budget. In a first paper (Part I, Remaud et al., 2023a), a COS intercomparison was carried out based on a set of reference surface fluxes for all processes (i.e., non‐optimized fluxes); the results pointed out some shortcomings in the COS global budget that need to be resolved. In this Part II, we extend the analysis by evaluating model simulations that use two versions of the optimized COS fluxes with available independent data, mostly obtained from aircraft platforms.…”

Carbon and Water Fluxes of the Boreal Evergreen Needleleaf Forest Biome Constrained by Assimilating Ecosystem Carbonyl Sulfide Flux Observations

“…Currently, a major challenge of using COS as a global‐scale GPP proxy is the imbalance of the global COS budget, as recently highlighted in the intercomparison of atmospheric COS transport models conducted by Remaud et al. (2023). A previous inversion study by Ma et al.…”

“…Currently, a major challenge of using COS as a global-scale GPP proxy is the imbalance of the global COS budget, as recently highlighted in the intercomparison of atmospheric COS transport models conducted by Remaud et al (2023). A previous inversion study by Ma et al (2021) has suggested the likely presence of a missing COS source in the tropics, and an underestimated COS sink in northern high latitudes.…”