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)(n)COOH (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)(n)COOH) = (9.35 +/- 2.08) x 10(-14) cm(3) molecule(-1) s(-1). For n = 2-4, k(OH + F(CF2)(n)COOH) = (1.69 +/- 0.22) x 10(-13) cm(3) molecule(-1) s(-1). Dimerization constants for 2F(CF2)(n)COOH = (F(CF2)(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(CF2)(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(CF2)(n)COOH. The major atmospheric removal mechanism for F(CF2)(n)COOH is believed to be wet and dry deposition which probably occurs on a time scale of the order of 10 days.