'Inverse modeling and sensitivity studies in atmospheric chemistry: aerosols, emissions, and direct radiative forcing.' Daven Henze Sulfate and carbonaceous aerosols are important for understanding the human impact on both air quality and climate change. Adjoint sensitivity analysis and inverse modeling is presented as a method for improving model estimates of the sources of these aerosols and for estimating the effects of individual sources on direct radiative forcing. The adjoint of a global chemical transport model (GEOS-Chem) is presented, focusing on the chemical and thermodynamic relationships between sulfate - ammonium - nitrate aerosols and their gas-phase precursors. Explicit inclusion of the processes that govern secondary formation of inorganic aerosol is shown to afford efficient calculation of sensitivities with respect to key model parameters such as anthropogenic emissions and uncertain reaction rate constants. A range of adjoint modeling applications is discussed. Initially we consider speciated measurements of aerosol sulfate and nitrate from surface monitoring stations. Sensitivities with respect to the discrepancy between model predictions and observations are used for gradient based optimization (inverse modeling) of aerosol sources, in particular emissions of ammonia. Application as a tool for air quality attainment studies are also shown. Additionally, preliminary results are presented on the use of the adjoint model to estimate the sensitivity of direct climate forcing of sulfate and carbonaceous aerosols with respect to anthropogenic emissions at a resolution commensurate with that of the emissions inventories.