## 5 Conclusions  
In this study, the behavior and diffusion of CO\({}_{2}\), assumed to have leaked from the seafloor, were numerically predicted for the first time near the one of the candidate sites for CO\({}_{2}\) ocean geological storage in Korea. The behavior of leaked CO\({}_{2}\) bubbles were analyzed numerically using a multi-scale ocean model to assess its environmental impacts, which is essential for obtaining public acceptance. The main parameters chosen for the simulation were leakage rates and initial diameters of CO\({}_{2}\) bubbles. The former was assumed to be 3800, 50,000, and 100,000 t/y and the latter to be 5, 10, and 20 mm, respectively. A total of five simulations were carried out by combining these parameters.  
From the simulation results, it was found that all CO\({}_{2}\) bubbles were dissolved into the seawater before reaching the free surface in all cases. As the leakage rate increased, relatively higher values were concentrated near the leakage depth, and wider areas of \(\Delta\)pCO\({}_{2}\) were observed because more bubbles existed and dissolution lasted for a longer time. As the initial diameter of the bubbles increased, the rising distance of the bubbles also increased due to the larger buoyant force of the relatively large volume of the bubble. However, small \(\Delta\)pCO\({}_{2}\) values were estimated when the diameter was 10 mm. For the mass transfer rates, though they were similar for the 5 and 20 mm diameters, they were reduced when the diameter was 10 mm.  
Figure 13: Contour maps of \(\Delta\)pCO\({}_{2}\) on the planes, where the full-3D small-scale domain is located, of the mesoscale domain at 30 days after the start of leakage with the same leakage rates of 100,000 t/y and leakage area of 20,000 m\({}^{2}\) but different initial diameters of the bubble. (a) yz plane (x = 81,000 m); (b) xz plane (y = 10,500 m); (c) xy plane near leakage area (z = 180 m)The estimated maximum \(\Delta\)pCO\({}_{2}\) for the extreme case was approximately 200 ppm during 30 days of leakage under the present simulation conditions. Therefore, it can be said that the environmental impact caused by the leakage of CO\({}_{2}\) was not significant.  
The present numerical model is expected to be useful and applicable not only for estimation of the behaviors and environmental impact of leaked CO\({}_{2}\) but for various purposes, such as determination of the proper location for leakage monitoring devices during ocean geological storage of CO\({}_{2}\).  
Scenario-based simulations and parametric studies will be performed in the near future. The main parameters, such as the leakage depth closely related to the phase of the leaked CO\({}_{2}\), the vertical distributions of the scalar properties according to the seasonal change, and the shape of the leakage area, will be considered. Furthermore, validation and improvement of adopted sub-models will be continued as uncertainties and assumptions remain, although well-known or validated ones were implemented in the present model.  
Conceptualization, S.-M.J. and W.-Y.S.; Methodology, S.-M.J. and W.-Y.S.; Validation, S.K.; Formal Analysis, S.K.; Investigation, W.-Y.S. and S.-M.J.; Resources, S.-M.J. and S.K.; Writing--Original Draft Preparation, S.-M.J.; Writing--Review and Editing, S.-M.J. and W.-Y.S.; Visualization, S.K.; Supervision, S.-M.J. and W.-Y.S.; Funding Acquisition, S.-M.J. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (No. 2017R1D1A3B03030031).  
The authors declare no conflict of interest.