CAIRT development support: SF6 in the Belgian Assimilation System for Chemical ObsErvations (BASCOE)

The Brewer-Dobson circulation (BDC) strength is predicted to increase due to growing greenhouse gas concentrations. Trends in the BDC are extremely uncertain. To resolve this, better estimates of age of air, a proxy for BDC strength, are necessary. This is one of the aims of the CAIRT mission. Age of air is typically computed from measurements of long-lived trace gases or simulated in a model using either idealised model tracers or real chemical species such as SF6. To evaluate the capabilitties of CAIRT, we will use the Belgian Assimilation System for Chemical ObsErvations (BASCOE) to assimilate simulated observations produced by the Chemical Lagrangian Model of the Stratosphere (CLaMS). To do this, the BASCOE model first needed to be updated with the chemistry of SF6. The update is validated through the calculation of the atmospheric lifetime of SF6 and other species and by comparing the simulated SF6 with satellite measurements.