With every breath the astronauts take, theyÕre using up oxygen that must be replenished. The ARS makes sure that new <a href="text">oxygen</a> and <a href="text">nitrogen</a> are being added to the crew compartment to replace the air that has already been breathed. The ARS does more than that, though. With every exhalation, the Shuttle crew members are releasing unbreathable carbon dioxide into the environment. The CO2 must be removed from the atmosphere, otherwise the crew members will get sick. The cabin fans of the ARS circulate the air in the crew compartment and filter it over <a href="text">carbon dioxide scrubbers</a> that remove carbon dioxide from the air.
