Atmospheric lifetime of sulphur hexafluoride (SF6) and five other trace gases in the BASCOE model driven by three reanalyses

Abstract

In this work, sulphur hexafluoride (SF6), which is often used as a tracer for stratospheric transport due to its inertness in the stratosphere and nearly linear growth rate in the troposphere, is included in the chemistry transport model (CTM) of the Belgian Assimilation System for Chemical ObsErvations (BASCOE). Sink and recovery reactions for this species are implemented in the model, which has a top in the mesosphere at 0.01 hPa. The simulated SF6 distributions are compared with MIPAS and ACE-FTS observations and the global atmospheric lifetime is computed from CTM runs driven by three recent meteorological reanalyses: ERA5, MERRA2 and JRA-3Q. The results show that BASCOE SF6 profiles are generally within 10 % of the satellite observations below 10 hPa, although discrepancies increase at higher altitudes. The global atmospheric lifetime is used as an additional diagnostic for the implementation of the chemistry in the mesosphere, where satellite measurements are unavailable. The derived SF6 lifetimes are 2646 years with ERA5, 1909 years with MERRA2 and 2147 years with JRA-3Q, in accordance with recent literature. Due to the large spread of published lifetimes for SF6, the study is extended to N2O, CH4, CFC-11, CFC-12 and HCFC-22, to validate the SF6 results. The lifetimes for these species are in agreement with previously reported values, and their spread between simula�tions is smaller compared to SF6. This analysis highlights the sensitivity of SF6 to the input reanalysis data sets and thus to differences in dynamics