Sensitivity analysis of a mixed-phase chemical mechanism using automatic differentiation

A sensitivity analysis of a comprehensive mixed-phase chemical mechanism is conducted under a variety of atmospheric conditions. The local sensitivities of gas and aqueous phase species concentrations with respect to a variety of model parameters are calculated using the novel automatic differentiation ADIFOR tool. The main chemical reaction pathways in all phases, interfacial mass transfer processes, and ambient physical parameters that affect tropospheric O-3 formation and O-3-precursor relations under all modeled conditions are identified and analyzed. The results show that the presence of clouds not only reduces many gas phase species concentrations and the total oxidizing capacity but alters O-3-precursor relations. Decreases in gas phase concentrations and photochemical formation rates of O-3 can be up to 9% and 100%, respectively, depending on the preexisting atmospheric conditions. The decrease in O-3 formation is primarily caused by the aqueous phase reactions of O-2(-) with dissolved HO2 and O-3 under most cloudy conditions.