Abstract
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(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.
Highlights
Hydrofluorocarbons (HFCs) have been developed as replacements for chlorofluorocarbons and hydrochlorofluorocarbons (HCFCs) to protect the stratospheric ozone layer from depletion
Difluoromethane (HFC-32, CH2F2) has been used as a refrigerant to replace HCFC-22 (CHClF2): azeotropic mixtures of CH2F2 with HFC-125 (CHF2CF3) and HFC-134a (CH2FCF3) have been used as refrigerants for air-conditioning and refrigeration for a few decades, and CH2F2 alone has recently been used as a refrigerant for airconditioning
In the inert-gas stripping (IGS) method experiment, an aqueous solution was purged with N2 to strip CH2F2 from the solution into the N2 purge gas flow, and the partial pressure of CH2F2 (Pt ) in the N2 purge gas flow decreased with time
Summary
Hydrofluorocarbons (HFCs) have been developed as replacements for chlorofluorocarbons and hydrochlorofluorocarbons (HCFCs) to protect the stratospheric ozone layer from depletion. By using AGAGE data in combination with a chemical transport model such as the AGAGE 12-box model (Cunnold et al, 1994; Rigby et al, 2013) and a value of 5.1 years as the atmospheric lifetime of CH2F2, O’Doherty et al (2014) estimated the global emission rate of CH2F2 in 2012 to be 21 ± 11 Gg yr−1 with an increase rate of 14 ± 11 % yr−1 Such estimates on the basis of long-term observational data such as the AGAGE and the National Oceanic and Atmospheric Administration Global Monitoring Division (NOAA GMD) network are called top– down estimates and have been shown to provide an independent and effective method for assessing the accuracy of globally and regionally aggregated reductions or increases in emissions of individual HFCs, as well as other greenhouse gases, compiled from national reports to the United Nations Framework Convention on Climate Change (e.g., Prinn et al, 2000; Lunt et al, 2015; Montzka et al, 2015)
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