For calculating DAC carbon footprint, the amount of CO2 captured is subtracted from the sum of the carbon footprints of the energy, adsorbents, and equipment materials and manufacturing. The second metric is carbon removal efficiency (η 𝐶𝑂 2 𝑟𝑒𝑚𝑜𝑣𝑎𝑙 ), which is typically multiplied by 100 and expressed as a percent. The carbon removal efficiency is the negative of carbon footprint, or the amount of CO2 emitted subtracted from the amount captured, normalized to the amount captured. A positive carbon removal efficiency indicates that more CO2 is captured than emitted, and a negative efficiency indicates more CO2 emitted than captured. A CO2 capture process with no environmental impacts has a carbon removal efficiency of 100%.