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
(CS2). The modelled COS mixing ratios were assessed
against in-situ observations from surface stations and aircraft.