Particle/gas partitioning for semi-volatile organic compounds (SVOCs) in level III multimedia fugacity models: Both gaseous and particulate emissions

Abstract

Multimedia fugacity models have long been used to address the fate of toxic organic chemical emissions by providing a quantitative account of the sources, transport processes, and sinks. Recently, we have examined three level-III fugacity models (E4F (equilibrium six-compartment four-fugacity), S6F (steady-state six-compartment six-fugacity) and S4F (steady-state six-compartment four-fugacity) Models), in the context of their performance set against real-world data, and their practicality of application. Here, we discuss how the balance between gaseous and aerosol phases of emissions assumed for initial conditions affects the different model outcomes. Our results show that the S6F Model predictions closely match those of the S4F Model when chemical emissions are entirely in the gas-phase. As the particulate proportion of the emission increases, the S6F Model predictions diverge from those of the S4F Model and approach those of the E4F Model. Once the particulate portion reaches 100%, the S6F and E4F Models produce identical results: an internally inconsistent system where chemicals are not in a steady state between air and aerosols, and mass balance for both air and aerosols is not achieved. Thus, in terms of practicality, internal consistency, chemical mass balance and agreement with observations, the S4F Model is clearly the best choice.