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, KeqS (in M atmg-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 KeqS value in water, which corresponds to the Henry's law constant (KH), at 298 K was determined to be 0.065 M atmg-1. The salinity dependence of KeqS (the salting-out effect), ln(KH/KeqS), did not obey the Sechenov equation but was proportional to S0.5. Overall, the KeqS(T) value was expressed by ln(KeqS(T)) Combining double low line g-49.71 + (77.70-0.134 × S0.5) × (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.