(8c) Investigating Atmospheric Inorganic Aerosol Sensitivity Relationships Through Thermodynamics and Population Dynamics

Atmospheric aerosols alter climate and can harm human health.  Characterizing the chemical state and sizes of aerosols as these effects occur is challenging due to complex atmospheric processing.  Quantitative estimates of the impact of aerosols are often sought through mathematical representations of the chemical and physical transformations occurring throughout the atmospheric residence time (i.e., chemical transport modeling).  These models must account for both directly emitted aerosol and contributions from precursor gases through nonlinear pathways.  The complexity of the system obscures relationships between the system input and output; thus, extensive modeling efforts are required to provide predictive modeling capabilities.  An alternative approach employs sensitivity analysis, which provides quantitative estimates of the effect of a selected condition (i.e., concentration of a precursor gas) on a final value (i.e., aerosol component concentration).  The adjoint of a model efficiently elucidates the sensitivity of a selected model output to a number of input values. 

The regional Community Multiscale Air Quality model is used to investigate regional-scale scientific questions and to quantify emissions controls necessary to attain air quality standards.  Within it, condensation and evaporation of inorganic gaseous species are modeled by thermodynamic equilibrium with ISORROPIA (Nenes et al, 1998; Fountoukis and Nenes, 2007), and aerosol population dynamics are quantified by a three-moment scheme (Whitby et al., 1991; Whitby and McMurry, 1997; Binkowski and Roselle, 2003).  In this work, the recently developed adjoint of these aerosol processes is employed to elucidate sensitivity relationships of inorganic aerosol populations to concentrations of aerosol species and precursor gases.  In particular, this work focuses on the ammonium-nitrate-sulfate-sodium-chloride aerosol system.  Finally, sensitivities are determined for atmospheric conditions commensurate with summer in the northeastern United States.