Development of a model to simulate CO2 releases underwater from shallow depths or deepwater is presented. It can simulate CO2 releases from a single point, or releases spread over an area (non-point source). The physico-chemical processes included are: gas expansion during upward travel due to pressure changes; gas dissolution and its impact on bubble volume; continuous recalculation of bubble buoyant velocity based on the volume and density changes; and tracking the transport and dispersion of dissolved and free gas respectively. The model uses multi-species Lagrangian parcels approach. Multiply sized bubbles, different phases, and their transformation from one to another are allowed. Volume and density changes in gas bubbles are computed by using non-ideal gas equation allowing for compressibility. CO2 concentrations and pH changes in seawater are computed for different scenarios of CO2 releases. pH value in seawater can change slightly after many hours of release for the cases considered.