Development of the adjoint of GEOS-Chem D. K. Henze, A. Hakami, and J. H. Seinfeld California Institute of Technology, Pasadena, CA, USA
Abstract. 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 adjoint
model is constructed from a combination of manually and automatically derived
discrete adjoint algorithms and numerical solutions to continuous adjoint
equations. Explicit inclusion of the processes that govern secondary
formation of inorganic aerosol is shown to afford efficient calculation of
model sensitivities such as the dependence of sulfate and nitrate aerosol
concentrations on emissions of SOx, NOx, and NH3. The
accuracy of the adjoint model is extensively verified by comparing adjoint to
finite difference sensitivities, which are shown to agree within acceptable
tolerances. We explore the robustness of these results, noting how
discontinuities in the advection routine hinder, but do not entirely
preclude, the use of such comparisons for validation of the adjoint model.
The potential for inverse modeling using the adjoint of GEOS-Chem is assessed
in a data assimilation framework using simulated observations, demonstrating
the feasibility of exploiting gas- and aerosol-phase measurements for
optimizing emission inventories of aerosol precursors.
Citation: Henze, D. K., Hakami, A., and Seinfeld, J. H.: Development of the adjoint of GEOS-Chem, Atmos. Chem. Phys., 7, 2413-2433, doi:10.5194/acp-7-2413-2007, 2007.