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Published May 11, 2007 | Published
Journal Article Open

Development of the adjoint of GEOS-Chem


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.

Additional Information

© Author(s) 2007. This work is licensed under a Creative Commons License. Received: 4 October 2006 – Published in Atmos. Chem. Phys. Discuss.: 19 October 2006. Revised: 6 February 2007 – Accepted: 17 April 2007 – Published: 11 May 2007. This work was supported by U.S. Environmental Protection Agency, grant R832158, and the National Science Foundation, grant NSF ITR AP&IM 0205198, which provided access to the TeraGrid resources at the National Center for Supercomputing Applications. We wish to thank M. Kopacz and A. Sandu for valuable insight and technical support.

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