# Direct Air Capture: How Engineers Are Pulling Carbon Dioxide Straight from the Atmosphere

The concentration of carbon dioxide in Earth's atmosphere has climbed well above 420 parts per million, a level that drives ongoing climate disruption. Unlike point-source carbon capture, which intercepts emissions at a smokestack before they disperse, direct air capture (DAC) technology pulls CO₂ directly from ambient air — a mixture in which the target gas represents less than 0.05% of total volume. That extreme dilution is what makes DAC both technically demanding and energetically expensive compared to industrial flue-gas capture. Despite those challenges, engineers and chemists have developed several distinct technological pathways that demonstrate measurable CO₂ removal at increasing scales (Custelcean, 2021).

The fundamental mechanism behind DAC relies on creating a strong chemical or physical affinity between a sorbent material and CO₂ molecules as air passes through a contactor. Once the sorbent is saturated, a regeneration step — typically involving heat, pressure changes, or both — releases the concentrated CO₂ so the sorbent can be reused. The captured gas can then be permanently stored underground or used as a feedstock for fuels and materials. Because atmospheric CO₂ is so dilute, moving enough air across the sorbent surface to achieve meaningful capture rates demands both clever engineering of contactors and careful optimization of the full process cycle (Shakouri Kalfati et al., 2025).

What makes DAC strategically significant is that it can, in principle, address historical emissions rather than only future ones. Carbon removal from the air is not a substitute for reducing emissions at their source, but it fills a role that no other single technology covers: drawing down the cumulative stock of atmospheric CO₂ that has already accumulated over decades of industrial activity. That role has attracted substantial research investment and, more recently, initial commercial deployment — though the path from laboratory demonstration to gigaton-scale removal involves challenges spanning chemistry, energy supply, water use, and cost (OBrien, 2024).

The Two Main Technological Families: Liquid Solvents and Solid Sorbents

DAC systems broadly divide into two categories based on the capture medium they employ. Liquid solvent systems typically use strongly alkaline solutions — most commonly potassium hydroxide — to absorb CO₂ from air into a carbonate solution, which is then regenerated at high temperatures, often exceeding 900°C. This process is energy-intensive but benefits from established industrial engineering principles borrowed from the pulp and paper industry's lime cycle. Solid sorbent systems, by contrast, use functionalized materials such as amine-grafted silica, metal-organic frameworks, or ion-exchange resins that bind CO₂ at lower temperatures and can be regenerated at temperatures ranging roughly from 80°C to 120°C, which opens the possibility of using low-grade waste heat (Custelcean, 2021).

The choice of sorbent has cascading effects on system design, energy consumption, and lifecycle cost. Solid sorbents operating at lower regeneration temperatures hold potential for significant efficiency gains, but they introduce their own engineering complications: water vapor in ambient air can compete with CO₂ for binding sites on some amine-based materials, and mechanical degradation of the sorbent over repeated capture-regeneration cycles affects long-term performance. Dynamic modeling tools developed specifically for solid-sorbent DAC systems allow researchers to simulate these cyclic processes, accounting for temperature gradients, sorbent loading curves, and airflow patterns across the contactor bed — information that is critical for scaling pilot systems to commercial installations (Shakouri Kalfati et al., 2025).

The Role of Enzymes: Biological Catalysts in a Chemical Process

A less conventional but scientifically documented approach introduces biological catalysts — specifically the enzyme carbonic anhydrase — into the DAC process. Carbonic anhydrase is naturally occurring in many living organisms, where it catalyzes the rapid interconversion of CO₂ and bicarbonate ion in biological fluids. Researchers have investigated whether this enzyme can accelerate the absorption of CO₂ from air into liquid solvent systems, potentially allowing capture to proceed at lower alkalinity or higher speed than purely chemical processes allow. Laboratory-scale experiments have demonstrated that enzyme-assisted systems can increase CO₂ absorption rates into buffered solutions under controlled conditions (Zaghini, 2025).

The practical challenge with enzyme-assisted DAC lies in stability. Industrial DAC processes expose sorbents to harsh conditions — high temperatures during regeneration, variable humidity, and the mechanical stress of continuous cycling — that can denature proteins and destroy catalytic activity. Research has therefore focused on immobilization strategies that anchor carbonic anhydrase to solid supports or encapsulate it within protective matrices, extending its operational lifetime under process conditions. While enzyme-assisted capture has not yet been deployed at commercial scale, the approach documents a potential route to reducing the energy penalty of absorption by enhancing reaction kinetics in the liquid phase (Zaghini, 2025).

Why Direct Air Capture Must Pull Carbon from Unfiltered Atmosphere

Direct air capture targets carbon dioxide at its most dispersed—floating freely in ambient air at concentrations around 420 parts per million—rather than at emission sources like power plants or factory stacks. This fundamental shift in approach matters because roughly half of global emissions come from diffuse sources: agriculture, transportation, buildings, and natural systems we can't easily pipe to a single filter. By pulling carbon straight from the air itself, engineers bypass the bottleneck of point-source capture and create a technology that works anywhere on Earth.

The physics underlying this process hinges on molecular selectivity. When ambient air passes through either a liquid solvent or solid sorbent, CO₂ molecules preferentially bind to the material while nitrogen and oxygen—which make up 99% of air—pass through largely untouched. Research by Gebald et al. (2020) demonstrated that certain solid sorbents can achieve selectivity ratios exceeding 1,000:1, meaning the material captures CO₂ at rates far higher than competing gases would. This selectivity is what makes direct air capture feasible at all, yet it also creates the central engineering challenge: pulling a needle from an atmospheric haystack requires enormous volumes of air to flow through the capture medium.

Temperature and pressure shifts drive the release of captured carbon. Once a sorbent or solvent reaches saturation with CO₂, heating or depressurizing the material causes the gas to desorb and concentrate into a pure stream. This concentrated carbon can then be compressed, transported, and either stored underground or converted into products—chemicals, fuels, or building materials. The energy cost of this heating cycle remains the primary economic barrier to scaling.

What makes direct air capture particularly powerful is its location flexibility. Unlike fossil fuel infrastructure, which must be built near reserves, or renewable energy plants, which need sun or wind, direct air capture installations can operate anywhere humans exist or have caused carbon accumulation. As climate scenarios increasingly demand we remove legacy emissions alongside cutting new ones, this ability to capture carbon from the air we breathe becomes not just a technical option, but a growing necessity.

Energy, Infrastructure, and the Path to Commercial Scale

Energy consumption is the single largest factor governing the cost and climate benefit of DAC. If the electricity and heat powering a DAC plant come from fossil fuels, the net CO₂ removal per unit energy input can be negligible or even negative. Studies have examined configurations in which DAC systems are integrated with low-carbon energy sources — including nuclear, geothermal, and renewable electricity — to maximize the climate benefit of each unit of energy consumed. In the United States context, initial engineering designs for DAC with carbon utilization and storage have been evaluated under programmatic criteria focused on technical readiness levels that move systems from laboratory demonstration toward full-scale commercial operation (OBrien, 2024).

Beyond energy, infrastructure for geological CO₂ storage is a prerequisite for permanent removal rather than simple carbon recycling. Compressed CO₂ must be transported to injection sites where it can be mineralized or stored in saline aquifers or depleted hydrocarbon reservoirs. The integrated engineering challenge — capture system, compression train, transport pipeline, and storage well — means that DAC projects require coordination across multiple industrial sectors simultaneously. Cost estimates for current commercial DAC systems range from several hundred to over one thousand US dollars per tonne of CO₂ removed, with projections that learning-by-doing and economies of scale could reduce costs substantially over coming decades, though such projections depend heavily on assumptions about energy prices and technology improvement rates (OBrien, 2024).

Practical Implications for Climate Strategy

DAC technology today occupies a position defined by demonstrated scientific feasibility, incomplete commercial maturity, and genuine uncertainty about the trajectory of cost reduction. Solid sorbent systems benefit from open-source dynamic models that allow independent researchers and engineers to test process configurations without rebuilding computational tools from scratch, accelerating the iteration cycle between design and deployment (Shakouri Kalfati et al., 2025). Enzyme-assisted approaches offer a documented alternative mechanism for improving absorption kinetics, particularly relevant for low-temperature or aqueous-phase capture systems (Zaghini, 2025). What the field needs is not simply more laboratory demonstrations but coordinated investment in full-system engineering at scales large enough to test real-world integration of capture, energy supply, and geological storage — the combination that determines whether DAC can contribute meaningfully to atmospheric CO₂ reduction at the scale the climate problem demands (Custelcean, 2021; OBrien, 2024).