The cleanliness of the air in space plays an important role in the life and health of astronauts. Generally speaking, the space in the aircraft cabin is small and airtight, and the non-metallic materials and instruments in the astronauts and the cabin are volatilizing various harmful gases at any time, which requires the "environmental control and life protection" sub-system to take effective measures to strictly control the harmful gases in the cabin and ensure air quality.

Dong Wenping, director of the Chinese astronaut Research and Training environmental control and health protection Research laboratory, said that the Shenzhou-9 mission astronauts in Tiangong-1 Shenzhou-9 complex to stay for ten days, and the space of the complex is only 60 cubic meters, to purify the cabin air, need to solve three problems. One is to purify the carbon dioxide that astronauts breathe. Carbon dioxide is the cause of cabin air purification, and too high a concentration can endanger the health of astronauts. It is usually required that the partial pressure of carbon dioxide in the cabin should not be greater than 1 kpa, and the alarm should be alerted when it reaches 2 kpa. The second is trace harmful gases, which are volatilized by non-metallic materials in the cabin under closed conditions, and the longer the cabin is closed, the higher the concentration of harmful gases. The third is particulate matter or microbes contained in the atmosphere itself.

Dong Wenping said that at present, to solve these three harmful gases, there are two main ways: one is to purify the fan, about 20 days before the launch of Shen9, Tiangong 1 has started the purification fan to purify the cabin air. The purification fan introduces the atmosphere in the cabin into the purification tank, and after chemical decomposition and absorption, the clean air flows back into the cabin. The purification fan is the key to the normal operation of the air purification device, and its energy consumption is low, which is only equivalent to the energy consumption of an ordinary lamp. In order to improve the reliability of the air purification device, the two-machine scheme is adopted. Once the main fan fails, it can automatically switch to the working state of the auxiliary fan immediately to ensure that the purification fan is always in the working state. Another purification method is to set activated carbon and a small amount of normal temperature catalyst in the purification tank to form a combined purification device to absorb trace harmful gases in the aircraft cabin, which is more suitable for spacecraft short-term flight spacecraft.

Dong Wenping said that the air quality in the combination of spacecraft and target aircraft has specific limits, and the inhalable particles per square meter also need to be controlled within a certain range, which is equivalent to the standard of a 100,000 level purification space, and the purification level is like the final assembly plant of the ground aircraft.