Direct Air Capture Definition, Working Principle, and Comparison

Direct air capture is the active removal of atmospheric CO2 through a suction and chemical treatment mechanism that extracts air directly from the atmosphere and removes its CO2 content. This article discusses direct air capture definition, working principle and comparison, as outlined below;





-Direct Air Capture Definition: 4 Ways to Define Direct Air Capture

-How Direct Air Capture Works

-Difference Between CCS and DAC







Direct Air Capture Definition: 4 Ways to Define Direct Air Capture

Direct air capture is the act and process of removing carbon dioxide directly from the atmosphere, in order to achieve environmental decarbonization.

The above is a very basic description of the DAC concept. It can further be understood when described as a ‘technology’, and this is shown in the alternative direct air capture definition below;

Direct air capture (DAC) is a carbon removal technology that is effective for removing greenhouse gases directly from the atmospheric gas stream, thereby mitigating climate change and protecting the ecosystem [1].

Below is another direct air capture definition that highlights how the technology works;

Direct air capture is an environmental remediation technique whereby large powerful fan systems are used to draw air into a collector unit that is equipped with sorbent chemicals like sodium hydroxide (NaOH) and potassium hydroxide (KOH), that chemically convert CO2 in the air to non-toxic materials that can be released safely into the environment [3].

Lastly, the direct air capture definition is outlined based on benefits of direct air capture;

Direct air capture is a component of green economies that is used to facilitate sustainable manufacturing and clean energy transition, while mitigating climate change and global warming [2].





How Direct Air Capture Works

Direct air capture works through a three-step process of collection, chemical conversion, and removal. Each of these three steps is discussed below;




1). Collection (in explanation of How Direct Air Capture Works)

Collection is the first step in the direct air capture process, and it involves a suction mechanism that draws significant volume of air into the direct air capture system.

While the specific details and functions of direct air capture technology may differ from one case to another, there is always a mechanism for air collection.

In a typical direct air capture plant, this mechanism is comprised of a fan system that works at high velocity to create a gas pressure gradient that pulls in air into the collector unit.




2). Chemical Conversion

In chemical conversion, the collected air is made to come in contact with an absorption column or unit that is equipped with sorbent chemicals.

Potassium hydroxide (KOH) is an example of a sorbent chemical used for chemical conversion in direct air capture systems.

The chemical reacts with air to convert carbon from its atmospheric form to a more storable form.




3). Removal (in explanation of How Direct Air Capture Works)

Direct air capture technology includes a mechanism for effective carbon removal.

Often, this is in form of a mechanically-driven conveyance column that sends carbon into a storage system, that is often a geologic formation.

Carbon removal works in similar manner to naturally-inducer carbon sequestration, that increases the quantity of sequestered carbon in soil.

This means that direct air capture intersects with the concept of carbon capture and storage (CCS). It is in fact a form of carbon capture and storage, as it performs the functions outlined in the term (that is; capture and storage). In some contexts, the addition of storage functionality to direct air capture is referred to as ‘direct air capture and storage‘; DAC+S.

Completion of the removal stage in direct air capture indicates that decarbonization has been achieved.

Removal can also be used to analyze various attributes of direct air capture; such as rate (in tons per unit time), and cost (cost per ton).

An Elaborate Illustration of Direct Air Capture Process (Credit: JoseZZ 2017 .CC BY-SA 4.0.)
An Elaborate Illustration of Direct Air Capture Process (Credit: JoseZZ 2017 .CC BY-SA 4.0.)





Difference Between CCS and DAC

The main difference between CCS and DAC is in terms of scope; where carbon capture and storage (CCS) is a broad concept that includes capture and storage of carbon dioxide from all sources, while direct air capture (DAC) is a distinctive technique for capture of only atmospheric carbon dioxide.

Carbon capture and storage can be used to decarbonize electricity generation and sustainable manufacturing processes, so that greenhouse gases are removed from flue gases before they are released into the environment.

On the other hand, direct air capture removes excess greenhouse gases that have already entered into the environment. This means that by comparison, CCS can be viewed as a predominantly pretreatment mechanism, while DAC is solely used for post-treatment.

The concept of CCS is more developed and mature than the concept DAC. In terms of practical application, it is more common for CCS to be recognized as a common, accepted and applicable concept than DAC.


Below is a tabulation of the differences between CCS and DAC;


Comparison Criteria



Relative scope



Type of remediation

Post treatment

Pre and Post-treatment



Capture, storage

Relative adoption level








Direct air capture is a remedial technology that collects air directly from the atmosphere, and strips it of its CO2 content through chemical absorption.

Three distinct process-steps outline how direct air capture works, as follows;

1. Collection

2. Chemical Conversion

3. Removal

The difference between carbon capture and storage and direct air capture lies in scope, with CCS having a much broader scope of both context and functionality, than DAC.






1). Beuttler, C.; Charles, L.; Wurzbacher, J. (2019). “The Role of Direct Air Capture in Mitigation of Anthropogenic Greenhouse Gas Emissions.” Frontiers in Climate 1:10. Available at: (Accessed 1 January 2023).

2). Breyer, C.; Fasihi, M.; Bajamundi, C. J. E.; Creutzig, F. (2019). “Direct Air Capture of CO2: A Key Technology for Ambitious Climate Change Mitigation.” Joule 3(9). Available at: (Accessed 1 January 2023).

3). Leonzo, G.; Fennell, P. S.; Shah, N. (2022). “Analysis of Technologies for Carbon Dioxide Capture from the Air.” Appl. Sci. 2022, 12(16), 8321. Available at: (Accessed 1 January 2023).

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