A kinetic chemistry tagging technique and its application to modelling the stable isotopic composition of atmospheric trace gases

摘要

Isotope composition, in many cases, holds unique\udinformation on the sources, chemical modification and sinks\udof atmospheric trace gases. Vital to the interpretation\udand use of an increasing number of isotope analyses is\udappropriate modelling. However, the exact implementation\udof isotopic information in chemistry-climate models is\uda challenge, and often studies use simplifications which\udlimit their applicability. Here we implement a thorough\udisotopic extension in MECCA, a comprehensive kinetic\udchemistry sub-model. To this end, we devise a generic\udtagging technique for the kinetic chemistry mechanisms\udimplemented as the sub-submodel MECCA-TAG. The\udtechnique is diagnostic and numerically efficient and\udsupports the investigation of various aspects of kinetic\udchemistry schemes. We focus specifically on the application\udto the modelling of stable isotopic composition. The\udresults of MECCA-TAG are evaluated against the reference\udsub-submodel MECCA-DBL, which is implicitly full detailed,\udbut computationally expensive and thus suboptimal\udin practical applications. Furthermore, we evaluate\udthe elaborate carbon and oxygen isotopic mechanism\udby simulating the multi-isotope composition of CO and\udother trace gases in the CAABA/MECCA box-model.\udThe mechanism realistically simulates the oxygen isotope\udcomposition of key species, as well as the carbon isotope\udsignature transfer. The model adequately reproduces the\udisotope chemistry features for CO, taking into account the\udlimits of the modelling domain. In particular, the mass-independently\udfractionated (MIF) composition of CO due\udto reactions of ozone with unsaturated hydrocarbons (a\udsource effect) versus its intrinsic MIF enrichment induced\udin the removal reaction via oxidation by OH is assessed.\udThe simulated ozone source effect was up to +1‰ in\udD(elta)17O(CO). The versatile modelling framework we employ\ud(the Modular Earth Submodel System, MESSy) opens the\udway for implementation of the novel detailed isotopic\udchemistry treatment in the three-dimensional atmospheric chemistry\udgeneral circulation model EMAC. We therefore\udalso present estimates of the computational gain obtained by\udthe developed optimisations.