Experimental determination of Henry's law constants of difluoromethane (HFC-32) and the salting-out effects in aqueous salt solutions relevant to seawater

Gas-to-water equilibrium coefficients, K-eq(S) (in Matm(-1)), of difluoromethane (CH2F2), a hydrofluoro-carbon refrigerant (HFC-32), in aqueous salt solutions relevant to seawater were determined over a temperature (T) range from 276 to 313K and a salinity (S) range up to 51% by means of an inert-gas stripping method. From the van't Hoff equation, the K-eq(S) value in water, which corresponds to the Henry's law constant (K-H), at 298K was determined to be 0.065 M atm(-1). The salinity dependence of K-eq(S) (the salting-out effect), ln (K-H/K-eq(S)), did not obey the Sechenov equation but was proportional to S-0.5. Overall, the K-eq(S)(T) value was expressed by ln(K-eq(S)(T)) = -49.71 + (77.70 - 0.134 X S-0.5) x (100 / T) + 19.14 x ln (T / 100). By using this equation in a lower-tropospheric semi-hemisphere (30-90 degrees S) of the Advanced Global Atmospheric Gases Experiment (AGAGE) 12-box model, we estimated that 1 to 4% of the atmospheric burden of CH2F2 resided in the ocean mixed layer and that this percentage was at least 4% in the winter; dissolution of CH2F2 in the ocean may partially influence estimates of CH2F2 emissions from long-term observational data of atmospheric CH2F2 concentrations.