Sensitivity and uncertainty analysis of the mechanism of gas-phase chlorine production from NaCl aerosols in the MAGIC model

This paper presents a global sensitivity and uncertainty analyses of the chlorine chemistry included in the Model of Aqueous, Gaseous and Interfacial Chemistry (MAGIC). Uncertainty ranges are established for input parameters (e.g. chemical rate constants, Henryʹs law constants, etc.) and are used in conjunction with Latin hypercube sampling and multiple linear regression to conduct a sensitivity analysis which determines the correlation between each input parameter and the model output. The contribution of each input parameter to the uncertainty in the model output is calculated by combining the results of the sensitivity analysis with the input parametersʹ uncertainty ranges. The peak concentration of molecular chlorine, [Cl2(g)]peak, is used to compare model runs since MAGIC has demonstrated previously the importance of an interfacial reaction between OH(g) and Cl−(aq,surface) in the production of Cl2(g). Results indicate that the interface reaction rate is most strongly correlated with [Cl2(g)]peak and is most responsible for the uncertainty in MAGICʹs ability to calculate precisely [Cl2(g)]peak. In addition, the mass accommodation coefficient for OH and the aqueous-phase reaction rate for Cl2 + OH− → HOCl + Cl− and 2CO3− + O2 + 2H2O → 2CO2•H2O + 2O2− also contribute significantly to the uncertainty in [Cl2(g)]peak.