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

Abstract

Relative rate techniques were used to study the kinetics of the reactions of OH radicals with a homologous series of perfluorinated acids, F(CF 2 ) n COOH ( n = 1, 2, 3, 4), in 700 Torr of air at 296 ± 2 K. For n > 1, the length of the F(CF 2 ) n group had no discernible impact on the reactivity of the molecule. For n = 1, k (OH + F(CF 2 ) n COOH) = (9.35 ± 2.08) × 10 -14 cm 3 molecule -1 s -1 . For n = 2−4, k (OH + F(CF 2 ) n COOH) = (1.69 ± 0.22) × 10 -13 cm 3 molecule -1 s -1 . Dimerization constants for 2F(CF 2 ) n COOH = (F(CF 2 ) n COOH) 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(CF 2 ) n COOH 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(CF 2 ) n COOH. The major atmospheric removal mechanism for F(CF 2 ) n COOH is believed to be wet and dry deposition which probably occurs on a time scale of the order of 10 days.