Development of the adjoint of GEOS-Chem

[摘要] We present the adjoint of the global chemical transport model GEOS-Chem,focusing on the chemical and thermodynamic relationships between sulfate –ammonium – nitrate aerosols and their gas-phase precursors. The adjointmodel is constructed from a combination of manually and automatically deriveddiscrete adjoint algorithms and numerical solutions to continuous adjointequations. Explicit inclusion of the processes that govern secondaryformation of inorganic aerosol is shown to afford efficient calculation ofmodel sensitivities such as the dependence of sulfate and nitrate aerosolconcentrations on emissions of SO_x, NO_x, and NH₃. Theaccuracy of the adjoint model is extensively verified by comparing adjoint tofinite difference sensitivities, which are shown to agree within acceptabletolerances. We explore the robustness of these results, noting howdiscontinuities in the advection routine hinder, but do not entirelypreclude, the use of such comparisons for validation of the adjoint model.The potential for inverse modeling using the adjoint of GEOS-Chem is assessedin a data assimilation framework using simulated observations, demonstratingthe feasibility of exploiting gas- and aerosol-phase measurements foroptimizing emission inventories of aerosol precursors.

[学科分类] 大气科学