Direct air capture

Direct air capture (DAC) is the use of chemical or physical processes to extract carbon dioxide directly from the ambient air.^[1] If the extracted CO₂ is then sequestered in safe long-term storage (called direct air carbon capture and sequestration (DACCS)), the overall process will achieve carbon dioxide removal and be a "negative emissions technology" (NET).

The carbon dioxide (CO₂) is captured directly from the ambient air; this is contrast to carbon capture and storage (CCS) which captures CO₂ from point sources, such as a cement factory or a bioenergy plant.^[2] After the capture, DAC generates a concentrated stream of CO₂ for sequestration or utilization or production of carbon-neutral fuel. Carbon dioxide removal is achieved when ambient air makes contact with chemical media, typically an aqueous alkaline solvent^[3] or sorbents.^[4] These chemical media are subsequently stripped of CO₂ through the application of energy (namely heat), resulting in a CO₂ stream that can undergo dehydration and compression, while simultaneously regenerating the chemical media for reuse.

When combined with long-term storage of CO₂, DAC is known as direct air carbon capture and storage (DACCS or DACS^[5]). It would require sustainable energy to power since approximately 400kJ of energy is needed per mole of CO₂ capture. DACCS can act as a carbon dioxide removal mechanism (or a carbon negative technology), although as of 2023^[update] it has yet to be integrated into emissions trading because, at over US$1000,^[6] the cost per tonne of carbon dioxide is many times the carbon price on those markets.^[7]

DAC was suggested in 1999 and is still in development.^[8][9] Several commercial plants are planned or in operation in Europe and the US. Large-scale DAC deployment may be accelerated when connected with economical applications or policy incentives.

In contrast to carbon capture and storage (CCS) which captures emissions from a point source such as a factory, DAC reduces the carbon dioxide concentration in the atmosphere as a whole. Thus, CCS is recommended for large and stationary sources of CO₂ rather than distributed and movable ones. On the contrary, DAC has no limitation on sources.^[2]