Drivers of Perfluorocarboxylic Acid (PFCA) Gas-Particle Partitioning: Modeled Properties and Observational Constraints

TREVOR VANDENBOER, Mayré Rodriguez Ramirez, Eric Vanhauwaert, Nasrin Dashti, Yashar Ebrahimi-Iranpour, Jessica Clouthier, Shira Joudan, Ye Tao, RenXi Ye, Cora Young, York University

     Abstract Number: 455
     Working Group: Aerosol Chemistry

Abstract
The atmospheric fate of perfluorocarboxylic acids (PFCAs) is attracting increasing attention due to the role of the atmosphere in global transport of these hazardous chemicals. There is a gap in our understanding of their gas-particle partitioning, limited by available measurements, and accurate partitioning properties. We model phase partitioning of C2-C14 PFCAs in the atmosphere including deprotonation and phase partitioning equilibria among air, aerosol liquid water, and particulate water-insoluble organic matter using a range of model-derived PFCA properties. Water and organic matter content are systematically varied across a full range of atmospheric conditions. Except during severe organic matter pollution episodes, shorter-chain PFCAs are predicted to mainly partition between air and aqueous phases, while for C12 and longer PFCAs, organic matter becomes the dominant particle phase sink. The partitioning framework underestimates the particle fraction of C2-C8 PFCAs compared with several ambient observations, with discrepancies increasing for longer-chain PFCAs. One to three orders of magnitudes higher particle/gas equilibrium ratios are required to fulfill the agreement. The discrepancy could result from externally mixed dust components, non-ideality of aerosol liquid water, and missed interactions between organic matter and charged PFCA molecules. Alternatively, time integrated high-volume sampling or inadequate recognition of their acidic properties could result in sampling error and/or bias. High time resolution and selective measurements of ambient PFCAs are needed to improve environmental fate modeling of ambient PFCAs and the new technique of AIM-IC-MS capable of measuring the gas and particle phases simultaneously on hourly timescales will be presented.