The two forms of carbon capture are point source capture and direct air capture (DAC). Point source capture pulls CO2 from industrial exhaust, like the smokestacks of power plants and cement factories, where the gas is concentrated. Direct air capture pulls CO2 straight from the open atmosphere, where it’s far more diluted. Both aim to prevent carbon dioxide from driving climate change, but they work in fundamentally different ways, cost different amounts, and serve different roles in the bigger picture.
Point Source Capture: Catching CO2 at the Smokestack
Point source capture intercepts carbon dioxide where it’s most concentrated: at the facilities that produce it. Power plants, steel mills, cement factories, and refineries all release exhaust gases (called flue gas) that contain a relatively high percentage of CO2. Because the concentration is so much greater than what’s floating around in open air, separating it out is more straightforward and less energy-intensive than pulling it from the atmosphere.
There are three main approaches to point source capture, each defined by when in the process the CO2 gets removed:
- Post-combustion capture removes CO2 from exhaust gases after fuel has been burned. This is the most common approach for existing power plants because it can be retrofitted onto facilities already in operation. The flue gas passes through chemical solvents or filters that selectively grab the CO2 molecules, then release them for collection.
- Pre-combustion capture converts the fuel into a mix of hydrogen and carbon monoxide before burning it. That carbon monoxide is then converted into CO2 and separated out, leaving hydrogen as a cleaner-burning fuel. This approach works well in facilities designed around gasification.
- Oxy-fuel combustion burns fuel in pure oxygen instead of regular air. The result is exhaust made up almost entirely of CO2 and water vapor. Removing the water is simple, leaving behind a nearly pure stream of carbon dioxide ready for compression and transport.
Most carbon capture systems at industrial facilities target 90% efficiency, meaning they stop nine out of every ten CO2 molecules from reaching the atmosphere. That 90% figure has been the baseline goal for decades because it hits the sweet spot between worthwhile climate impact and practical engineering. Some operational projects have exceeded 95%, and engineers believe 98 to 99% capture is technically achievable. Even at 99%, though, the remaining exhaust from a coal plant would still contain CO2 at concentrations equal to or higher than the surrounding atmosphere.
Direct Air Capture: Pulling CO2 From Thin Air
Direct air capture works on a completely different problem. Instead of catching emissions at their source, DAC technologies extract CO2 that’s already dispersed into the atmosphere. This makes it uniquely powerful: it can theoretically clean up emissions from any source, including cars, planes, and agriculture, and even address CO2 released decades ago. The tradeoff is difficulty. Atmospheric CO2 is roughly 0.04% of the air, far more dilute than the exhaust from a power plant or cement kiln. Filtering out those sparse molecules demands significantly more energy.
Two main technologies drive DAC systems:
- Liquid solvent systems pass air through a chemical solution (typically a form of dissolved calcium or potassium compound) that reacts with and absorbs CO2. The solution is then heated to release the captured CO2 in concentrated form. The process also involves converting quicklime to slaked lime in a regeneration loop, and the final CO2 is compressed for storage or use.
- Solid sorbent systems use materials that CO2 sticks to (adsorbs onto) at lower temperatures, then release it when heated. These systems can operate at lower temperatures than liquid solvent approaches, which opens up the possibility of using waste heat or renewable energy sources.
Performance and cost vary with environmental conditions. Temperature, humidity, and airflow all affect how quickly a DAC facility can capture CO2 and how much energy it uses. Liquid solvent systems, for instance, lose water to evaporation in hot, dry climates, adding to operational costs.
How Costs Compare
The cost gap between the two forms is significant. Point source capture benefits from working with concentrated CO2, which keeps costs lower per ton removed. Direct air capture, dealing with vastly more diluted CO2, has historically been far more expensive.
In 2011, a review by the American Physical Society estimated DAC would cost around $600 per ton of captured CO2. That number has dropped substantially. One prominent estimate published in the journal Joule put the cost between $94 and $232 per ton, depending on the system design and local energy costs. That’s a dramatic improvement, but still generally higher than point source capture for equivalent amounts of CO2. The cost difference comes down to thermodynamics: extracting a molecule from a concentrated stream simply requires less energy than finding and grabbing that same molecule when it’s scattered across open air.
What Happens to Captured CO2
Once CO2 is captured by either method, it goes one of two directions: permanent storage underground or industrial use. Geological storage involves injecting compressed CO2 into deep rock formations, including depleted oil and gas reservoirs, deep saline reservoirs, and unmineable coal seams. These are structures that have naturally trapped fluids and gases for millions of years, making them well-suited for long-term containment.
The most common industrial use for captured CO2 is enhanced oil recovery, where it’s pumped into aging oil fields to push out remaining crude. Other uses include building materials, synthetic fuels, and chemical feedstocks, though these remain smaller-scale. The climate benefit depends heavily on the end use. Permanent geological storage locks the carbon away indefinitely. Using it to extract more oil offsets some of the benefit.
Where Things Stand Today
As of 2024, 50 commercial carbon capture facilities were operating worldwide, a 16.3% increase over the previous year. New facilities that came online added about 0.52 million tons of CO2 per year in capture capacity. That sounds like a lot, but global CO2 emissions run into the tens of billions of tons annually, so current capture capacity handles a tiny fraction of the problem.
Point source capture makes up the vast majority of operational capacity. DAC is still in its early stages, with only a handful of facilities running commercially. The two approaches aren’t competitors, though. Point source capture tackles the biggest, most concentrated emission sources right now. Direct air capture addresses the harder, longer-term challenge of cleaning up diffuse and legacy emissions that no smokestack filter can reach. Most climate roadmaps call for scaling both.