Articles | Volume 17, issue 12
Atmos. Chem. Phys., 17, 7495–7507, 2017
https://doi.org/10.5194/acp-17-7495-2017
Atmos. Chem. Phys., 17, 7495–7507, 2017
https://doi.org/10.5194/acp-17-7495-2017

Research article 21 Jun 2017

Research article | 21 Jun 2017

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

Shuzo Kutsuna Shuzo Kutsuna
  • National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba, 305-8569, Japan

Abstract. 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(KHKeqS), 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.

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Short summary
We experimentally determined gas-to-water equilibrium coefficients of difluoromethane, a refrigerant HFC-32, in aqueous salt solutions relevant to seawater at 3–39 °C to evaluate what portion of HFC-32 emitted into the atmosphere would be dissolved in the ocean. The portion in the ocean was estimated to be realistically limited to only about 1 % globally; however, in a lower-tropospheric semi-hemisphere (30 °S–90 °S), the portion was estimated to be at least 4 % in winter.
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