CCS or DAC: what is the difference between point-source capture and direct air capture?
In pathways toward carbon neutrality, carbon capture is emerging as a complementary tool alongside efforts to reduce emissions. Beyond clean-energy production technologies, some solutions aim directly to intercept or remove CO₂ in order to limit its accumulation in the atmosphere.
Among these, two approaches are attracting growing interest in industrial and scientific circles: capture at the source, known as CCS (Carbon Capture and Storage)), and direct capture from the air, or DAC (Direct Air Capture). Although they pursue a common objective, these technologies differ significantly in how they work, where they can be applied, and how mature they are.
CCS (Carbon Capture and Storage) captures CO₂ directly at the chimney of a factory or power plant, whereas DAC (Direct Air Capture) removes it from the ambient air — two complementary approaches, but fundamentally different in their rationale and their applications. The sections that follow first present a concise comparison of the two technologies.
CCS and DAC: two approaches to capturing CO₂
CCS and DAC mainly differ in where they act within the carbon cycle. The first captures CO₂ directly at the source, before it is emitted into the atmosphere, whereas the second acts downstream by extracting CO₂ already present in the ambient air. This structural difference influences how they operate, their costs, and their contexts of application.
A key factor behind this difference is the CO₂ concentration in the gas being treated. Concentration corresponds to the amount of carbon dioxide present in a gas, generally expressed as a percentage by volume or in parts per million (ppm).
CCS operates on gas streams with a high CO₂ content, coming from industrial flue gases or the effluents of cement plants and power stations. This higher concentration generally makes capture more technically efficient and less costly.
DAC, by contrast, treats ambient air where CO₂ is very dilute (about 420 ppm), which means treating large volumes of air to isolate significant quantities of carbon dioxide.
According to the U.S. Department of Energy, DAC is defined precisely by the fact that it does not rely on above-average CO₂ concentrations caused by nearby point sources [3].
Table 1 — CCS vs DAC: comparison of key parameters
| Parameter | CCS (capture at the source) | DAC (direct air capture) |
|---|---|---|
| Targeted CO₂ source | Concentrated industrial emissions | Ambient air (≈ 420 ppm) |
| CO₂ concentration treated | High (flue or process gas) | Very low (< 0.05 % vol.) |
| Typical location | On an industrial or energy site | Independent of emission sources |
| Type of technology | Absorption/adsorption on a gas stream | Closed-loop chemical or physical sorption |
| Main objective | Avoid emissions at the source | Remove emissions already present |
| Technological maturity | Commercial at large scale | Emerging |
(Sources: [1][2][3])
Complementary roles in the energy transition
This difference in operation translates into distinct roles within decarbonization strategies. The IRENA stresses that hard-to-decarbonize sectors — notably long-distance transport and heavy industry — require a combination of efficiency, electrification, hydrogen, renewable heat and, where necessary, CO₂ capture or removal. Within this logic, CCS intervenes where emissions can be intercepted at the source, whereas DAC plays a growing role in offsetting residual emissions that are hard to avoid, as well as in addressing historical releases already accumulated in the atmosphere [1]. Rather than opposing each other, these roles are complementary. This is why each process deserves to be examined separately.
CCS: capturing CO₂ at the chimney of industry
Carbon Capture and Storage (CCS), or in its broader form CCUS, which adds a dimension of utilization of the captured CO₂, is the most mature carbon-capture technology to date. Its principle rests on a simple logic: intercept the concentrated CO₂ before it is released into the atmosphere, directly where it is produced.
This process applies to large point sources of emissions, that is, to facilities whose CO₂ releases are concentrated and measurable. Key sectors include:
Power plants running on coal, gas or biomass, as well as cogeneration (CHP) facilities, which produce large volumes of CO₂-rich flue gas.
Processing industries: production of hydrogen, ammonia, cement and chemical products, whose processes generate concentrated emissions that are difficult to eliminate otherwise.
Natural gas fields, where CO₂ is often present in significant proportion in the extracted stream and must be separated before any use [6].
In each of these contexts, CO₂ is captured directly in the flue or process gases, at concentrations far higher than those of ambient air. This characteristic considerably reduces energy requirements compared with capture from the air. The U.S. DOE designates this approach by the term point-source carbon capture, that is, capture at the point source, targeting industrial processes, fuel transformation and electricity generation [2]. On a global scale, about 40 large commercial facilities already apply CCUS technologies, collectively capturing more than 45 million tonnes of CO₂ per year [2].
Transport and geological storage
Once captured, the CO₂ must be compressed, transported and then injected deep into underground geological formations — saline reservoirs, or depleted oil and gas fields — where it will be retained permanently. This geological storage of CO₂ therefore consists of immobilizing the captured gas in deep, impermeable and stable rock strata, so that it does not return to the atmosphere.
The potential storage methods are varied:
Injection into deep underground geological formations, such as saline aquifers or depleted oil reservoirs, is the most widespread and best-documented method.
Storage in the deep seabed represents an avenue still under study, although less developed commercially.
Industrial fixation in the form of inorganic carbonates offers a route for the mineralization of CO₂, transforming it into a stable solid material [6].
The IEA confirms that geological storage is a proven and effective means of permanently isolating captured CO₂ from the atmosphere [4]. It also recommends encouraging the development of CO₂ transport and storage hubs to support the decarbonization of industrial clusters and to promote the co-location of clean-energy technologies with geological storage sites [4].
Objectives and limits of CCS
The primary objective of CCS is to reduce emissions coming from concentrated industrial sources whose emissions are difficult to reduce through conventional alternatives. At the industrial project level, the IEA’s CCUS database tracks capture, transport, storage and utilization projects with an announced capacity of more than 100,000 tonnes per year [5].
This technology nevertheless has an inherent limitation: it cannot, on its own, address diffuse or historical emissions already present in the atmosphere. This limitation highlights the distinct role of direct air capture, which targets CO₂ already dispersed in the atmosphere.
DAC: removing CO₂ already present in the atmosphere
Unlike CCS, Direct Air Capture (DAC) is not positioned at the chimney of a factory. It tackles ambient air directly, where CO₂ is extremely dilute. This makes DAC a carbon removal technology, rather than a tool for preventing emissions at the source.
DAC is defined as a technology that regenerates a capture medium in a closed loop and/or uses a mechanical contactor to chemically or physically separate CO₂ directly from the ambient atmosphere, without relying on above-average CO₂ concentrations caused by nearby point sources [3].
Operation and location
On a technical level, DAC uses mechanical contactors that circulate ambient air through chemical sorbents — liquid or solid — that selectively trap CO₂. This sorbent is then regenerated by applying heat or pressure, releasing a concentrated stream of CO₂ ready to be stored or valorized. Unlike CCS, this approach is not geographically constrained by proximity to an emission source: it can in principle be deployed anywhere, ideally where clean energy is cheap and abundant, such as solar, wind or geothermal sites.
The DOE's definition also explicitly specifies that DAC excludes the separation of flue gases or concentrated industrial process gases, as well as any fundamental dependence on proximity to these sources [3]. This is what fundamentally distinguishes it from CCS and gives it a unique deployment flexibility.
Target concentration and energy challenges
DAC treats ambient air at about 420 ppm of CO₂, a concentration nearly 300 times lower than that of a typical industrial flue gas. This extreme dilution forces facilities to treat very large volumes of air to isolate a significant amount of carbon dioxide — which inevitably translates into higher energy requirements per tonne of CO₂ captured.
The energy source used to operate a DAC facility therefore plays an important role in its overall climate performance. For the process to deliver meaningful net CO₂ removal, it should ideally be powered by low-carbon energy sources, such as renewables, geothermal energy or nuclear power. By contrast, a DAC system that relies heavily on fossil fuels could reduce, or even undermine, the expected climate benefits.
Objectives and role in net-zero scenarios
DAC occupies a growing place in international climate pathways, precisely because it can act where other solutions cannot. According to the IEA, it makes it possible in particular to:
Offset hard-to-avoid emissions in long-distance transport and heavy industry, where direct electrification remains limited.
Act on historical emissions already accumulated in the atmosphere, opening the way to net-negative emissions — an objective that goes beyond mere carbon neutrality [1].
In the IEA's Net Zero Emissions by 2050 scenario, DAC technologies will need to capture more than 85 MtCO₂ in 2030 and about 980 MtCO₂ in 2050, starting from a current capacity of almost 0.01 MtCO₂ per year [1]. This massive scale-up underscores the magnitude of the technological and industrial challenge to be met in the coming decades.
To summarize its distinctive characteristics, DAC stands out for:
Its geographic flexibility: it can be installed independently of any industrial source, where clean energy is available.
Its atmospheric removal capacity: unlike CCS, it makes it possible to achieve net-negative emissions by removing CO₂ already present in the air.
Its complementarity with CCS: it is not intended to replace it, but to extend the reach of decarbonization to diffuse and historical emissions.
Its status as an emerging technology: still in its commercial scale-up phase, its long-term climate potential is considerable.
Conclusion
The current state of deployment illustrates the different roles of these two approaches. CCS is already operating at industrial scale, with about 40 commercial facilities worldwide capturing more than 45 MtCO₂ per year [2]. DAC, by contrast, remains an emerging technology, but the IEA projects that it could reach nearly 980 MtCO₂ per year by 2050 in its Net Zero scenario [1].
This difference in maturity does not place the two technologies in opposition. Rather, it highlights their complementarity: CCS aims to reduce emissions at the source, while DAC opens the possibility of removing CO₂ already present in the atmosphere.
As these technologies develop, their deployment will also depend on favorable geological, energy and industrial conditions. Underground exploration, geological storage and carbon-capture infrastructure are therefore closely connected components of the energy transition, a field that Squatex follows with interest.
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References
[1] International Energy Agency (IEA). Direct Air Capture: A Key Technology for Net Zero. IEA, 2022. https://iea.blob.core.windows.net/assets/78633715-15c0-44e1-81df-41123c556d57/DirectAirCapture_Akeytechnologyfornetzero.pdf
[2] U.S. Department of Energy. Point-Source Carbon Capture. Office of Fossil Energy and Carbon Management, 2024. https://www.energy.gov/sites/default/files/2024-04/point-source-carbon-capture.pdf
[3] U.S. Department of Energy. Direct Air Capture: Definition and Company Analysis Report. Office of Clean Energy Demonstrations, 2025. https://www.energy.gov/sites/default/files/2025-01/Direct%20Air%20Capture%20Definition%20and%20Company%20Analysis%20Report.pdf
[4] International Energy Agency (IEA). CO2 Storage Resources and Their Development: An IEA CCUS Handbook. OECD/IEA, 2022. https://www.oecd.org/content/dam/oecd/en/publications/reports/2022/12/co2-storage-resources-and-their-development_a64875ef/9f492c0b-en.pdf
[5] International Energy Agency (IEA). CCUS Projects Database. IEA, 2024. https://www.iea.org/dat/ccus-projects-database
[6] Intergovernmental Panel on Climate Change (IPCC). "Carbon Dioxide Capture and Storage." Fourth Assessment Report — Working Group III, ch. 4, section 4.3.6. IPCC, 2007. https://archive.ipcc.ch/publications_and_data/ar4/wg3/en/ch4s4-3-6.html
