Modeling PFAS in the global atmosphere – the PRIEST extension for the ICON-ART modeling framework

This study presents the ICON-ART (ICOsahedral Non-hydrostatic model framework with Aerosol and Reactive Tracers) PRIEST (PFCA Reactions In Earth System Transport) model extension, developed to simulate the transport and transformation of Per- and Polyfluorinated Substances (PFAS) in the atmosphere. While the ICON-ART framework was developed to simulate atmospheric physics and chemical composition, the newly developed PRIEST extension incorporates additional gas-phase and aqueous physics, along with chemical reaction mechanisms, to model the transport, transformation, and deposition of Perfluoroalkyl Carboxylic Acids (PFCA) precursors. Therefore, the model includes 22 aqueous-phase reactions that depend on liquid cloud water and temperature. The aqueous-phase processes represent the adsorption of precursors in water droplets, with variable absorption rates. The model follows a hierarchical initialization, starting with the emissions, followed by aerosols, chemistry, and finally removal. To efficiently represent the atmospheric oxidative environment, PFAS chemistry is implemented in a semi-offline framework forced by prescribed monthly mean oxidant fields from CAM-chem. ... mehrA simple parameterization of the OH radical is implemented to improve the simulation of PFCA precursors. The global model results (approximate to 105 km2 grid resolution and 6 h temporal resolution) show the capability of the model system to simulate regional and global variations of PFCA concentrations and their deposition processes. The results reveal an overestimation of atmospheric concentrations observed in Europe and an underestimation in East Asia. These differences are mainly related to the coarse spatial model resolution and the uncertainties arising from the underlying emissions model. In conclusion, ICON-ART PRIEST represents a significant step forward in simulating the atmospheric fate of PFCAs precursors and their transformation products by integrating an enhanced chemical mechanism into the ICON-ART framework that couples both gas-phase and aqueous-phase processes, and also with the incorporation of a detailed temporally resolved PFAS emission inventory.