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Perfluoroalkyl carboxylic acids (PFCAs) are environmental contaminants thatare highly persistent, bio-accumulative, and have been detected along withtheir atmospheric precursors far from emissions sources. The importance ofprecursor emissions as an indirect source of PFCAs to the environment isuncertain. Modeling studies have used degradation mechanisms of differingcomplexities to estimate the atmospheric production of PFCAs, and thesediffering mechanisms lead to quantitatively different yields of PFCAs underdiffering atmospheric conditions. We evaluate PFCA formation with the mostcomplete degradation mechanism to date, to our knowledge, using a box modelanalysis to simulate the atmospheric chemical fate of fluorotelomerprecursors to long-chain PFCAs. In particular, we examine the variability inPFCA formation in different chemical environments, and estimate theuncertainty in PFCA formation due to reaction rate constants.  We calculate long-chain PFCA formation theoretical maximum yields for thedegradation of fluorotelomer precursor species at a representative sample ofatmospheric conditions from a three-dimensional chemical transport model, andestimate uncertainties in such calculations for urban, ocean, and Arcticconditions using polynomial chaos methods. We find that atmosphericconditions farther from pollution sources have both higher capacities to formlong-chain PFCAs and higher uncertainties in those capacities.  Our calculations of theoretical maximum yields indicate that under typicalNorthern Hemisphere conditions, less than 10 % of emitted precursor may reachlong-chain PFCA end products. This results in a possible upper bound of 2–50 t year<sup>−1</sup> of long-chain PFCA (depending on quantity of emitted precursor) producedin the atmosphere via degradation of fluorotelomer products. However,transport to high-yield areas could result in higher yields. While theatmosphere is a potentially growing source of long-chain PFCAs in the Arctic,oceanic transport and interactions between the atmosphere and ocean may berelatively more important pathways to the Arctic for long-chain PFCAs

Uncertainty and variability in atmospheric formation of PFCAs from fluorotelomer precursors