Solid carbon dioxide is stored under high pressure. this is because on decreasing the pressure on solid carbon dioxide , it gets converted directly into carbon dioxide gas . when a slab of solid carbon dioxide is kept exposed to air , then the pressure on it is reduced to normal atmospheric pressure ( 1 atm ) , its temperature rises and it starts changing to carbon dioxide. so this conversion is done by the decrease in pressure and atmospheric temperature. solid carbon dioxide is a white solid called dry ice. it is an extremely cold substance . it is used to deep freeze food and to keep ice cream cold. it can produce much lower temperatures than that produced by ordinary ice . so it is more effective in cooling purpose.