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

Abstract. Gas-to-water equilibrium coefficients, K_eq^S (in M atm⁻¹), of difluoromethane (CH₂F₂), a hydrofluorocarbon refrigerant (HFC-32), in aqueous salt solutions relevant to seawater were determined over a temperature (T) range from 276 to 313 K 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 298 K 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  ×  S^0. 5)  ×  (100∕T) + 19.14  ×  ln(T∕100). By using this equation in a lower-tropospheric semi-hemisphere (30–90 °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.