The pH distribution during CO2 dissolving into water under mid-depth sea condition

Sequestration of liquid CO₂ into the intermediate depth ocean has been considered as a means to reduce atmospheric concentration of this greenhouse gas and mitigate global warming. A number of CO₂ droplets are released and diluted into the intermediate ocean. The behavior of CO₂ dissolution is very important in order to control the concentration of CO₂ and to keep the environmental impact minimum. Under conditions in the intermediate ocean, that is, high pressure and low temperature, the CO₂ clathrate hydrate film was formed on the CO₂ droplet surface. The hydrate film has been considered to decrease the dissolution rate and the CO₂ concentration near the droplet surface. The authors applied a LIF technique with a new kind of the dye as a pH indicator. The new dye in the CO₂ dissolved water emitted intense fluorescence dependent on its pH. The visualized images showed the two dimensional distribution of the pH, i.e., CO₂ concentration, around the CO₂ droplet with or without the hydrate film.