Sulfur hexafluoride emissions for transport model evaluation

The EDGAR v8 emissions inventory of SF₆ forms the basis for fluxes between 1990 and 2021. These annual 0.1° x 0.1° emissions have been scaled to agree with estimates of annual emissions derived from the observed global growth rate, and with regional SF₆ emissions estimates from recent studies (Hu et al. 2023 for North America, An et al. 2024 for China, and Vojta et al. 2024 for Europe) . The global scaling goes from measured mole fractions to estimated atmospheric mass burden using an assumed constant atmospheric dry air mass of 5.1352E+18 kg (Trenberth and Smith 2005), and molar masses of 146.05 and 28.965 for SF₆ and dry air respectively. If these are persistently different from their models, participants are encouraged to scale input fluxes to match the growth rate of SF₆ in the atmosphere. Please consult with one of the intercomparison organizers if you are interested in doing this. To avoid discontinuities between years and to provide monthly fluxes, a smooth trend model has been applied. This is continuous from year-to-year, a quadratic function of month within a year, and has the property of preserving the annual total emissions (Rasmussen 1991). We have checked that the resultant surface flux is nonnegative for all time and space. While the source emissions data are at 0.1° x 0.1°, there also are 1° x 1° data available in this archive. The 0.1° x 0.1° dataset also has regional totals included, as well as the region masks used to translate between totals from various publications (above) and gridded emissions. Modelers may need to regrid the emissions for their particular modeling system. As total SF₆ burden will be a crucial criterion for evaluating simulations, it is vital that emissions be applied exactly and that this regridding is done conservatively. We suggest using the HEMCO emissions frontend in standalone mode to conservatively regrid emissions to each model’s emissions grid. For more complex grids, the SCRIP regridding tool can be used to perform this task. Intercomparison organizers will be available to help modelers develop emissions for their particular system. Please contact intercomparison organizers (Brad Weir, Sourish Basu, or Andy Jacobson) to discuss this procedure.