Atmospheric Chemistry of Perfluorinated Carboxylic Acids:  Reaction with OH Radicals and Atmospheric Lifetimes

Relative rate techniques were used to study the kinetics of the reactions of OH radicals with a homologous series of perfluorinated acids, F(CF2)nCOOH (n = 1, 2, 3, 4), in 700 Torr of air at 296 ± 2 K. For n > 1, the length of the F(CF2)n group had no discernible impact on the reactivity of the molecule. For n = 1, k(OH + F(CF2)nCOOH) = (9.35 ± 2.08) × 10-14 cm3 molecule-1 s-1. For n = 2−4, k(OH + F(CF2)nCOOH) = (1.69 ± 0.22) × 10-13 cm3 molecule-1 s-1. Dimerization constants for 2F(CF2)nCOOH = (F(CF2)nCOOH)2 were determined to be 0.32 ± 0.03 Torr-1, 0.30 ± 0.03 Torr-1, 0.41 ± 0.04 Torr-1, and 0.46 ± 0.05 Torr-1 for n = 1, 2, 3, 4, respectively. Atmospheric lifetimes of F(CF2)nCOOH with respect to reaction with OH radicals are estimated to be approximately 230 days for n = 1 and 130 days for n > 1. Reaction with OH radicals is a minor atmospheric fate of F(CF2)nCOOH. The major atmospheric removal mechanism for F(CF2)nCOOH is believed to be wet and dry deposition which probably occurs on a time scale of the order of 10 days.