Experimental study on the uptake ability of acid materials into the polycrystalline ice particles -Application to the mechanism of ozone hole development-

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Uni-directional growth experiments of ice crystals in the water including a solute of acid or salt were carried out using a newly developed growth apparatus in combination with a Mach-Zehnder interferometer. Both the pattern evolutions of ice/water interfaces and the distributions of solute concentrations in front of interfaces were observed simultaneously.The interfacial patterns, which were completely flat at the initial stage of the growth, were changed to those composed by the array of regular finger cells. Then the boundaries between the neighboring cells can be regarded as the grain boundaries. Consequently, it means that the regular row of grain boundaries was formed along the interfaces. The distributions of solute concentrations were determined by analyzing the shifts of interference fringes at the vicinity of interfaces, and the actual concentrations of solutes on the interfaces were also determined quantitatively. The uptake abilities of solutes into the ice crystals through the interfaces were first discussed using the results of both observations.As a result, we clarified that, when the interfacial patterns were still flat, the amount of solute rejected at the interface during the ice growth was completely consistent with the solute amount predicted by the calculation based on the equilibrium distribution coefficient of the solute against the ice crystal. However, as soon as the interfaces were changed to the perturbed ones, the mass balance of the solute completely disappeared. This means that the solutes were incorporated along the grain boundaries.In conclusion, we determined that the actual distribution coefficients are about 0.35. This value is extremelylarger than the equilibrium distribution coefficients (0.01 or less for almost all solutes). This result strongly suggests that the grain boundaries can incorporate a large quantity of acid solutes and the polycrystalline ice particles can work as a storehouse of acid materials.