Direct air capture

Direct air capture (DAC) is the use of chemical or physical processes to extract carbon dioxide (CO₂) directly from the ambient air.^[1] If the extracted CO₂ is then sequestered in safe long-term storage, the overall process is called direct air carbon capture and sequestration (DACCS), achieving carbon dioxide removal. Systems that engage in such a process are referred to as negative emissions technologies (NET).^[2]

DAC is in contrast to carbon capture and storage (CCS), which captures CO₂ from point sources, such as a cement factory or a bioenergy plant.^[3] 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^[4] or sorbents.^[5] 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.

As of 2023, DACCS has yet to be integrated into emissions trading because, at over US$1000,^[6] the cost per ton of carbon dioxide is many times the carbon price on those markets.^[7] The current high cost of DAC is driven by the scale of deployment and energy factors. It is reported that for DAC plant less than 50,000 tonnes CO₂ per annum, like the current largest DAC plant (Climeworks Mammoth), DAC costs would exceed $1000 per tonne CO₂.^[8] However, for plant scales of 1 Mtpa and above, DAC cost would generally be within $94–232 per tonne of atmospheric CO₂ removed.^[4][8] Future innovations may reduce the energy intensity of this process.

DAC was suggested in 1999 and is still in development.^[9][10] 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.^[3]