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. 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]). 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] For the end-to-end process to remain net carbon negative, DAC machines must be powered by renewable energy sources, since the process can be quite power intensive. Future innovations may reduce the energy intensity of this process.

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, DAC can be used to capture emissions that originated in non-stationary sources such as airplanes.^[2]