We define a DAC process as the process of capturing CO 2 from atmospheric air, i.e., separating the ultra-dilute CO 2 (today around 420 ppm) from other gases. This definition excludes the steps in which captured CO 2 is transported and stored or further conditioned to meet specific requirements imposed by the storage option. We refer to the latter as DACCS. A DAC plant mainly consists of a DAC unit, which interacts with the existing energy supply system, the material supply chain, and the CO 2 transport and storage infrastructure (if CO 2 is permanently stored). The considered system boundary of a DAC plant is illustrated in Figure . In general, the capture of CO 2 from the air requires input of both materials and energy, which can be either heat and/or electricity. As output, DAC processes deliver a more concentrated CO 2 stream, while they may also create waste (e.g., degraded solvent or sorbent material) and/or produce direct CO 2 emissions itself ('emitted CO 2 from flue gas' in Figure ). The purity of CO 2 output streams may vary from single percentages by volume to almost pure CO 2 , 3 depending on the technology used.