The Henry's law constant of trifluoroacetic acid and its partitioning into liquid water in the atmosphere

The Henry's law constant of trifluoroacetic acid [K(H') (mol kg^-1 atm^-1), for the equilibrium CF₃COOH((g)) ⇆ CF₃COOH((aq))] has been determined from measured partial pressures over aqueous solutions at 278.15, 298.15 and 308.15 K, and is given by: In(K(H')) = 9.099-9.328 x 10³(1/T(r)-1/T) where T (K) is temperature and T(r) is equal to 298.15 K. Accuracy is estimated to be ± 25% in K(H'), partly limited by uncertainties in the pK(a) of the acid (0.47 at all temperatures, from literature data). Trifluoroacetic acid in the atmosphere will partition entirely into fog and cloud water (0.05-1.0 g H₂O m^-3), but can reside in both phases for the liquid water contents typical of aerosols (10^-5-10^-4 g H₂O m^-3) depending on aerosol pH and to some extent on composition.