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

摘要

Gas-to-water equilibrium coefficients, KeqS (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 KeqS value in water, which corresponds to the Henry's law constant?(KH), at 298?K was determined to be 0.065?M?atm?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))??=???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.