The particular characteristics of confined space mean that it is easy for harmful substances to be produced and enriched. Moreover

the concentration of carbon dioxide in an enclosed space is strongly related with human health. In this paper

a new method is proposed in which carbon dioxide is removed from the air by reducing the air temperature to freeze and separate the carbon dioxide. Compared with traditional methods of removing carbon dioxide

the theoretical feasibility and advantages of the freezing method are analyzed. To verify the results of this theoretical analysis

an air purification system using liquid nitrogen as the cold source was designed. Experimental results show that the freezing method can remove carbon dioxide quickly. When the volume concentration of carbon dioxide is 1% and the volume flow of air is 100 L/min

it takes just 18 min to reduce the carbon dioxide concentration to less than 0.1%. The experiments also show that the freezing method of removing carbon dioxide can reach and maintain an extremely low carbon dioxide concentration of just 0.03%. This low concentration is hard to achieve by traditional methods.