Atmospheric processing describes the extraction of substances out of the Martian atmosphere and the usage as raw material for further processing. Unlike surface and sub-surface mining, the atmospheric mining does not require the movement of large amounts of regolith or rock with heavy machinery, nor is expensive transport per rover or railroad necessary. The atmosphere can simply be sucked in through a pipe at every location, and the processing is done inside of buildings. Also, the maintenance of all the mining machinery is in-house, which is a major safety advantage.
Collection of Atmosphere
A device similar to a vacuum pump collects Martian air. The collected gas is compressed to the habitat's internal pressure for easier handling.
Compression above 5,19 bar allows to liquefy carbon dioxide.
The atmosphere is cooled to remove water vapor as a condensate. As the gas continues to cool most of the rest of the water vapor is removed as frost. The dry gas is cooled further to remove carbon dioxide condensate. There will be more carbon dioxide than is needed for industrial purposes so some of it will be expanded to help power the compressors and to cool the incoming gas. Then excess CO2 will be discharged.
The 0.03 % water vapor (H2O) is equivalent to about 10 % air humidity after adiabatic compression and cooling to around 1°C. A device similar to an air dehumidifier can be used to extract this water.
Nitrogen and argon
The balance of the remaining gas after carbon dioxide condensation contains mostly nitrogen and argon. This mixture can serve as a buffer for oxygen to produce a breathable atmosphere, where Carbon monoxide must be catalytically removed.
Nitrogen can be separated out for use as ammonia and nitrates in fertilizer and as nitric acid in industry. Argon is useful for industrial processes that must be performed in an inert atmosphere.