Global atmospheric chemistry model for the fate and transport of PFCA and their precursors

• Published in: Environmental Science: Processes & Impacts
• Main Authors: Thackray, Colin P., Selin, Noelle E., Young, Cora J.
• Format: Text
• Language: English
• Published: 2020
• Subjects: Article; Arctic; Devon Ice Cap; Ice cap
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7050637/; http://www.ncbi.nlm.nih.gov/pubmed/31942888; https://doi.org/10.1039/c9em00326f

Perfluorocarboxylic acids (PFCA) are environmental contaminants that are highly persistent, many are bio-accumulative, and have been detected along with their atmospheric precursors far from emissions sources. The overall importance of precursor emissions as an indirect source of PFCA to the environment is uncertain. Previous studies have estimated the atmospheric source of PFCA using models and degradation pathways of differing complexities, leading to quantitatively different results. We present results from simulations of atmospheric PFCA formation and fate using the chemical transport model GEOS-Chem. We simulate the most up-to-date chemistry available to our knowledge for the degradation of the precursors fluorotelomer alcohol (FTOH), fluorotelomer olefin (FTO), and fluorotelomer iodide (FTI), as well as deposition and transport of the precursors, intermediates and end-products of the formation chemistry. We calculate yields of C3–C13 PFCA formed from 4:2–12:2 fluorotelomer precursors, and their deposition to the surface. We find that the ratio of long-chain to short-chain PFCA increases strongly with distance from source regions. We compare our model results to remote deposition measurements and mid-latitude rainwater measurements. The model captures the observed relationship between rainwater abundance and PFCA chain length, as well as the average deposition rates at mid-latitude and Arctic sites, but underestimates deposition of PFDoA, PFDA, and TFA at mid-latitudes and PFNA at the Devon Ice Cap. We provide estimates of cumulative PFCA deposition globally. We find that given the most recent emission inventory(1) the atmospheric source of PFCA is 6–185 t/yr globally and 0.1–2.1 t/yr to the Arctic.