Carbon Dioxide (CO2) is a toxic, atomically heavy chemical compound in a Gaseous State. It tends to sink below other gases. Duplicants exhale Carbon Dioxide and is generally one of the first problems a budding colony needs to tackle.

Algae Terrarium and Carbon Skimmer both scrub Carbon Dioxide from the air. Coal Generator, Natural Gas Generator, Petroleum Generator, and Polymer Press all generate Carbon Dioxide.