Direct air capture (DAC) is the use of chemical or physical processes to extract carbon dioxide (CO₂) directly from the ambient air. 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).

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. 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 or sorbents. 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, the cost per ton of carbon dioxide is many times the carbon price on those markets. 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. However, for plant scales of 1 Mtpa and above, DAC cost would generally be within $94–232 per tonne of atmospheric CO₂ removed. Future innovations may reduce the energy intensity of this process.

DAC was suggested in 1999 and is still in development. 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.

There are the three stages of CO₂ capture in DAC: the contacting stage, the capture stage, and the separation stage. In the contacting stage, the DAC system transports atmospheric air containing CO₂ to the equipment using large-scale fans. Subsequently, in the CO₂ capture stage, CO₂ rapidly and effectively binds with liquid solvents in chemical reactors or solid sorbents in filters, which must possess binding energies equivalent to that of CO₂. Later in the CO₂ separation stage, external energy sources facilitate the separation of CO₂ from the solvents or sorbents, yielding pure CO₂ and regenerated solvents or sorbents. Following the completion of these three stages, the separated pure CO₂ is either utilized or stored, while the recovered solvents or sorbents are recycled for reuse in the CO₂ capture process.

Generally, solid sorbents DAC (S-DAC) uses low temperature process DAC, while liquid (amine or metallic hydroxides) sorbents DAC (L-DAC) uses low or high temperature process. S-DAC and L-DAC feature different properties in terms of kinetics and heat transfers. Currently, L-DAC and S-DAC represent two mature technologies for industrial deployment. Additionally, several emerging DAC technologies, including electro-swing adsorption (ESA), moisture-swing adsorption (MSA), and membrane-based DAC (m-DAC), are in different stages of development, testing, or limited practical application.

More recently, Ireland-based company Carbon Collect Limited has developed the MechanicalTree™ which simply stands in the wind to capture CO₂. The company claims this 'passive capture' of CO₂ significantly reduces the energy cost of Direct Air Capture, and that its geometry lends itself to scaling for gigaton CO₂ capture.