Development of the adjoint of ISORROPIA II

Inverse modeling of atmospheric processes with chemical transport models (CTMs) provides a platform for improving the accuracy with which models represent reality and a means of reducing the uncertainty of model parameters, such as emissions estimates. Various techniques have been applied thus far with the adjoint method proving efficient for optimization of many parameters simultaneously. The high spatial and temporal variability of aerosol emissions requires this capability if adjustments are to be made by incorporating remotely sensed or in situ measurements. Treatment of aerosols within adjoints of CTMs has, until now, captured the behavior of only limited inorganic components. This work advances the capabilities of adjoints of CTMs markedly by providing a tool to execute inverse modeling of deliquesced aerosols with the same level of specificity as ISORROPIA II, the updated edition of a widely applied inorganic thermodynamic equilibrium model.

The adjoint of ISORROPIA II enables modelers to treat a system of deliquesced salts containing the species sodium, nitrate, sulfate, ammonium, chloride, potassium, magnesium, and calcium. The sodium and chloride species have not yet been treated in an adjoint of a thermodynamic equilibrium model nor have the crustal species that were added in the release of ISORROPIA II. Inclusion of these species significantly enhances the applicability of the thermodynamic equilibrium model adjoint, particularly for coastal areas and regions with significant dust contributions.