Direct air capture (DAC) is a process that uses chemical or physical methods to remove carbon dioxide (CO₂) directly from the air around us. When the captured CO₂ is stored safely for a long time, the process is called direct air carbon capture and sequestration (DACCS), which helps reduce CO₂ in the atmosphere. Systems that do this are known as negative emissions technologies (NET).

DAC differs from carbon capture and storage (CCS), which removes CO₂ from specific sources, like factories or power plants. After capturing CO₂, DAC creates a concentrated stream of CO₂ that can be stored or used. CO₂ removal happens when air interacts with special chemical materials, such as liquid solvents or absorbent substances. These materials are then heated to release the CO₂, which can be dried and compressed. The materials are also reused after this process.

As of 2023, DACCS is not part of emissions trading systems because it costs more than $1,000 per ton of CO₂ removed, which is much higher than the price of carbon in those markets. The high cost is due to the size of the operations and the energy needed. For example, a DAC plant that removes less than 50,000 tonnes of CO₂ each year, like Climeworks Mammoth, costs over $1,000 per tonne. However, larger plants that remove 1 million tonnes of CO₂ annually or more may cost between $94 and $232 per tonne. Future improvements might lower the energy needed for this process.

DAC was first proposed in 1999 and is still being developed. Some commercial plants are already operating or planned in Europe and the United States. Large-scale use of DAC could increase if it is paired with cost-effective uses or supported by government policies.

Unlike CCS, which captures CO₂ from specific locations like factories, DAC reduces CO₂ levels in the entire atmosphere. This makes DAC useful for capturing emissions from sources that are not fixed, such as airplanes.

Methods of capture

Direct Air Capture (DAC) involves three main steps: contacting, capturing, and separating CO₂. In the contacting stage, large fans move air containing CO₂ into the DAC system. During the capture stage, CO₂ in the air binds quickly with liquid solvents in chemical reactors or solid materials in filters. These materials must be strong enough to hold CO₂ securely. In the separation stage, energy is used to remove CO₂ from the solvents or materials, producing pure CO₂ and regenerating the solvents or materials for reuse. After these steps, the pure CO₂ is either used or stored, and the recovered materials are reused in the capture process.

Solid sorbent DAC (S-DAC) typically uses low-temperature processes, while liquid sorbent DAC (L-DAC), which uses solvents like amines or metallic hydroxides, can operate at low or high temperatures. S-DAC and L-DAC differ in how quickly they work and how heat moves through them. Both are well-developed technologies ready for industrial use. Other newer DAC methods, such as electro-swing adsorption (ESA), moisture-swing adsorption (MSA), and membrane-based DAC (m-DAC), are still being tested or used in limited ways.

A company in Ireland, Carbon Collect Limited, created the MechanicalTree™, a device that captures CO₂ passively by standing in the wind. The company says this method lowers energy costs and allows the technology to scale for capturing large amounts of CO₂.

Most commercial DAC systems use liquid solvents, such as amine-based or caustic solvents, to absorb CO₂ from air. For example, sodium hydroxide, a common caustic solvent, reacts with CO₂ to form sodium carbonate. Heating sodium carbonate produces pure CO₂ gas. Sodium hydroxide can be recovered from sodium carbonate through a process called causticizing. Alternatively, CO₂ can bind to solid materials through chemisorption. Heat and vacuum are then used to release CO₂ from the solid material.

Some specific chemical processes being studied include using alkali and alkali-earth hydroxides, carbonation, and organic-inorganic hybrid sorbents made of amines in porous materials.

The idea of using many small DAC units, similar to how plants work, to reduce CO₂ levels has led to the nickname "artificial trees" in the media.

In 2012, professor Klaus Lackner designed a process using an anionic exchange polymer resin called Marathon MSA. This material absorbs CO₂ from air when dry and releases it when exposed to moisture. The process uses energy from the phase change of water, but more research is needed to determine its cost-effectiveness.

Other materials being explored for CO₂ capture include metal–organic frameworks (MOFs).

Membrane-based DAC (m-DAC) uses semi-permeable membranes to separate CO₂. This method uses little water and has a smaller space requirement. Polymeric membranes, such as glassy or rubbery types, are often used. Glassy membranes are good at separating CO₂ but allow it to pass slowly. Membrane-based capture is still being developed and needs more research before large-scale use.

Electro-swing adsorption (ESA) is another method being studied.

Rock flour, which is soil ground into tiny particles by glacier ice, has potential as a soil conditioner and for CO₂ capture. Glaciers deposit about one billion tons of rock flour each year, and one ton of Greenlandic rock flour can capture 250 kilograms of carbon.

Environmental impact

Direct Air Capture (DAC) is a technology that removes more carbon dioxide (CO₂) from the air than it emits. When renewable energy is used, DAC releases about 0.01 tonnes of CO₂ for every tonne of CO₂ captured. However, when grid electricity and natural gas are used, it releases between 0.3 to 0.65 tonnes of CO₂ for every tonne captured. The type of energy used has the biggest effect on DAC’s total emissions. Using renewable wind energy and grid electricity together can still be carbon-negative, especially if wind energy provides at least 50–80% of the energy needed and grid electricity emissions are below 0.3077 kgCO₂ per kilowatt-hour. If grid electricity emissions are higher, they should be used less than 20% to keep carbon removal high.

Supporters of DAC say it is important for reducing climate change. Scientists believe DAC could help meet the goals of the Paris Agreement, which aims to limit global temperature increases to well below 2°C above pre-industrial levels. The International Energy Agency (IEA) estimates that capturing at least 85 million tonnes and 980 million tonnes of CO₂ annually by 2030 and 2050, respectively, is needed for net zero. However, some argue that relying on DAC could delay efforts to reduce emissions directly. They suggest that cutting emissions first may be a better solution. It is important to see DAC as a tool that works alongside other methods to reach climate goals.

Opponents of DAC say the technology needs a lot of resources, which might make it less effective. A 2020 study found that DAC 2 technology may not be able to capture the projected 30 gigatonnes of CO₂ per year because it would require massive amounts of materials, such as 16.3–27.8 gigatonnes of ammonia and 3.3–5.6 gigatonnes of ethylene oxide. The same study said DAC 1 technology would need at least 8.4–13.1 terawatt-years of energy, but this estimate did not include energy costs for storing captured CO₂. The IEA’s net zero goals, however, require capturing only 0.1 gigatonnes of CO₂ annually by 2050, which is much less than the 30 gigatonnes opponents mentioned.

Energy costs were studied in 2021. To keep DAC’s carbon removal rate between 73–86% per tonne of CO₂ captured, the technology would need land and renewable energy similar to what is required for switching all vehicles from gasoline to electric vehicles. It would also need about five times more materials than electric vehicles. Most of DAC’s material needs are common ones, like steel, concrete, and minerals such as zeolites and metallic hydroxides. Electric vehicles may also need critical materials, but these might not be available in enough quantity for net zero goals.

Some DAC systems, like liquid ones, need both high-temperature heat and electricity. These systems often use natural gas, grid electricity, or natural gas combustion to meet their energy needs. This means some DAC systems rely on fossil fuels, which they aim to reduce. However, even with natural gas use, DAC is still generally carbon-negative, emitting 0.3–0.65 tonnes of CO₂ for every tonne captured.

DAC that uses amine-based absorption requires a lot of water. To capture 3.3 gigatonnes of CO₂ annually, it would need 300 kilometers of water, or 4% of the water used for irrigation. In contrast, using sodium hydroxide needs less water, but the chemical is very dangerous. Different carbon removal methods have their own advantages. For example, nature-based solutions are cheaper, but a DAC plant that captures 1 million tonnes of CO₂ per year would need 0.4–1.5 square kilometers of land, which is similar to the CO₂ capture of about 46 million trees but would require 3,098–4,647 square kilometers of land.

DAC needs more energy than traditional methods that capture CO₂ from point sources like flue gas because the CO₂ in air is less concentrated. The minimum energy needed to extract CO₂ from air is about 250 kWh per tonne of CO₂, while capturing CO₂ from natural gas and coal plants requires about 100 and 65 kWh per tonne, respectively. Additional energy costs from using fans to move air could add 10–30% to the energy needed, depending on the system.

Applications

Practical uses of DAC include

• helping to get more oil from underground,
• making carbon-neutral synthetic fuel and plastics,
• adding carbon dioxide to drinks to make them fizzy,
• storing carbon dioxide underground to reduce its impact on the environment,
• making concrete stronger,
• creating a carbon-neutral alternative to traditional concrete,
• improving the growth of algae used for food or fuel,
• increasing the amount of carbon dioxide in greenhouses to help plants grow,
• producing liquid fuels,
• helping to get more methane gas from coal beds.

These uses require different amounts of carbon dioxide from the captured gas. Methods like storing carbon dioxide underground need very pure carbon dioxide (more than 99%), while uses like farming can work with less pure carbon dioxide (about 5%). Since the air processed by DAC starts with only 0.04% carbon dioxide (or 400 parts per million), creating very pure carbon dioxide requires more energy and is usually more expensive. Carbon dioxide used for food production often needs higher purity, ranging from 50% or more, followed by extra chemical steps.

DAC is not a replacement for traditional methods of capturing and storing carbon dioxide from specific sources, but it can work together with these methods. It can help manage carbon emissions from many different places, emissions that escape from carbon capture systems, and carbon that leaks from underground storage. Because DAC can be used far from where pollution happens, synthetic fuels made this way can use existing fuel transport systems.

Most discussions about DAC focus on its ability to help reduce climate change. However, most DAC facilities are small and mainly sell captured carbon dioxide for other uses instead of storing it permanently. Facilities that sell carbon dioxide for drinks operate with low recovery rates, capturing about 4.7% of carbon dioxide and producing 58 tons of carbon dioxide per day. Using DAC for commercial purposes shows that some people believe DAC is a way for companies to protect their financial interests.

Because DAC has many uses, supporters say its political value lies in its ability to create new job opportunities.

Operational/developing DAC facilities

Direct Air Capture (DAC) Projects and Their Processes for Removing or Storing Carbon

• By the end of 2024, 53 DAC plants are expected to be in operation.
• By 2030, 93 DAC plants are projected to be operating, with a combined ability to remove 6.4 to 11.4 million metric tons of carbon dioxide (CO₂) per year.
• By the end of 2024, 18 DAC plants will be operational in North America, and 24 will be operational in Europe.
• The leading countries involved in DAC projects include the United States, Canada, and European nations.

DAC technologies have been proposed to help China achieve its goal of carbon neutrality by 2060. After the 2021 Glasgow Climate Conference, China, the world’s largest emitter of greenhouse gases, began developing strategies to reduce emissions. If China uses DAC alone, it could reduce global warming by approximately 0.2 to 0.3 degrees Celsius. Studies on China’s path to carbon neutrality suggest that capturing and storing large amounts of CO₂ annually could help achieve this goal. China has created its own DAC technology, called "CarbonBox," developed by Shanghai Jiao Tong University and China Energy Engineering Corporation. Each CarbonBox module can remove over 100 metric tons of CO₂ per year, producing CO₂ that is 99% pure. CarbonBox facilities are the size of shipping containers, can be placed on-site, and use low-carbon energy sources to remove CO₂ from the air.

The Orca, developed by Climeworks in Zurich with support from Microsoft in 2021, was the first large-scale DAC plant. It was designed to remove 4,000 metric tons of CO₂ annually, which is equivalent to about 1.75 million liters of gasoline. However, since its operation began, the plant has averaged removing 600 metric tons of CO₂ per year, which is not enough to offset its own emissions. The Orca plant is located in Iceland at Hellisheidi and is powered by the Hellisheidi Geothermal Power Plant. It uses 12 special containers that capture about 600 kilograms of CO₂ per hour. The facility works with CarbFix, an Icelandic company that injects captured CO₂ into the Earth’s crust through a process called mineralization. This process prevents risks like fire or leaks that can occur with other DAC methods.

Octavia Carbon, founded in 2022 by Martin Freimüller, is the first DAC company in the Global South. The company plans to develop DAC technology that matches Kenya’s renewable energy grid and geology, which are suitable for storing CO₂. This project is still being developed, but with support from the Kenyan government and international DAC companies, the team now includes 53 or more employees. Octavia Carbon is working with Carbonfuture to use a new digital Monitoring, Reporting, and Verification (dMRV) system for DAC. This system tracks data in real time across the entire carbon removal process. The current pilot facility, called Project Hummingbird, is located in Kenya’s Rift Valley near Naivasha and is expected to capture and store 1,000 metric tons of CO₂ annually. Project Hummingbird will use mineralization by injecting CO₂ into basalt rock formations found in the Rift Valley.

Cost

One of the biggest challenges in using DAC is the cost of removing CO₂ from the air. At first, people hoped that DAC would cost about $100–$300 per tonne of CO₂. However, as of 2023, the actual cost is estimated to be over $1,000 per tonne of CO₂. The Department of Energy estimated costs to be under $100 per tonne, while other sources reported higher costs. A recent study found that the high cost is linked to the small size of most DAC plants, which typically capture less than 50,000 tonnes of CO₂ each year. Small plants cost more than $1,000 per tonne of CO₂ captured, while larger plants cost between $94–$232 per tonne. The largest DAC plant, Climeworks Mammoth, captures 36,000 tonnes of CO₂ annually at a cost of $1,000 per tonne. Larger DAC plants can lower costs through economies of scale, with costs ranging from $94–$232 per tonne for plants that capture 1 million tonnes of CO₂ annually. Policies that support DAC can help speed up large-scale use.

Under the Bipartisan Infrastructure Law, the U.S. Department of Energy will spend $3.5 billion to build four DAC hubs. These hubs could capture at least 1 million metric tonnes of CO₂ each year from the air. After capture, the CO₂ will be stored permanently in underground rock formations. The Department of Energy has already invested $1.2 billion to develop DAC projects in Texas and Louisiana. These projects were selected as part of President Biden’s Bipartisan Infrastructure Law.

Development

Carbon Engineering is a company that removes carbon dioxide from the air. It was started in 2009 and is supported by people like Bill Gates and Murray Edwards. In 2015, it began operating a test facility in British Columbia, Canada. This facility can remove about one ton of CO₂ each day. A study from 2015 to 2018 estimated the cost of removing CO₂ to be between $94 and $232 per ton. A 2025 report agreed with these costs, stating that if a DAC plant can remove at least one million tonnes of CO₂ per year, the cost would be between $97 and $168 per ton in 2025 and $87 and $140 per ton in 2050. The same report also noted that if a DAC plant can remove less than 50,000 tonnes per year, the cost could be over $1,000 per ton. Climeworks’ largest DAC plant, called Mammoth, removes 36,000 tonnes of CO₂ per year.

Carbon Engineering works with a company called Greyrock to turn some of the captured CO₂ into synthetic fuels like gasoline, diesel, and jet fuel. The company uses a solution made of potassium hydroxide, which reacts with CO₂ to form potassium carbonate, removing CO₂ from the air.

Climeworks’ first large-scale DAC plant started operating in 2017 in Switzerland. It can remove 900 tonnes of CO₂ per year and uses heat from a nearby waste incineration plant to reduce energy needs. The captured CO₂ is used to help grow plants in a nearby greenhouse. Climeworks estimates it costs about $600 to remove one ton of CO₂ from the air.

Climeworks partnered with Reykjavik Energy on a project called Carbfix, started in 2007. A later version, CarbFix2, began in 2017 and is funded by the European Union. This project is near a geothermal power plant in Iceland. In this process, CO₂ is injected deep underground, where it turns into solid minerals in basalt rock. The DAC plant uses heat from the power plant, reducing overall emissions.

On May 8, 2024, Climeworks opened the world’s largest DAC plant, called Mammoth, in Iceland. This plant can remove 36,000 tonnes of CO₂ annually, which is equivalent to removing emissions from about 7,800 gas-powered cars each year. The cost to capture CO₂ at this plant is reported to be $1,000 per ton. This high cost is due to the plant’s size, as larger plants generally have lower costs per ton. For a plant that removes one million tonnes of CO₂ per year, the cost would be between $94 and $232 per ton.

Global Thermostat is a company founded in 2010, based in New York, with a facility in Alabama. It uses special materials called amine-based sorbents attached to carbon sponges to remove CO₂ from the air. The company’s projects can remove between 40,000 and 50,000 tonnes of CO₂ per year. It claims to remove CO₂ at a cost of $120 per ton at its Alabama facility. Global Thermostat has agreements with Coca-Cola and ExxonMobil to use its technology for producing carbonated beverages and synthetic fuels.

Soletair Power is a startup founded in 2016 in Finland. It focuses on DAC and Power-to-X technologies, which create synthetic fuels and materials. The company is supported by Wärtsilä, a Finnish technology group. Soletair Power’s technology captures CO₂ from the air inside buildings using existing ventilation systems. The captured CO₂ is turned into concrete or used to make synthetic products like food, textiles, or fuel. In 2020, Wärtsilä, Soletair Power, and Q Power created a demonstration unit for Power-to-X in Dubai, which produces synthetic methane from captured CO₂.

Prometheus Fuels is a startup based in Santa Cruz, California. It was started in 2019 and uses DAC technology to remove CO₂ from the air. The CO₂ is converted into alcohols using electricity from renewable sources, then turned into gasoline and jet fuel. These fuels are carbon neutral because they do not release net CO₂ when used.

Heirloom opened its first DAC facility in Tracy, California, in 2023. This facility can remove up to 1,000 U.S. tons of CO₂ annually, which is mixed into concrete using technology from CarbonCure. Heirloom also has a contract with Microsoft to purchase 315,000 metric tons of CO₂ removal.

Other organizations involved in DAC include:
– Center for Negative Carbon Emissions (Arizona State University)
– Carbfix (a subsidiary of Reykjavik Energy, Iceland)
– Energy Impact Center (a research institute promoting nuclear energy for DAC)
– Mission Zero Technologies (a startup in London, UK)
– Carbyon (a startup in Eindhoven, the Netherlands)
– EDIBON (an initiative in Madrid, Spain, focused on education and research in emission capture)

In research, scientists at ETH Zurich developed a photoacid solution for DAC, which uses less energy and has a new chemical process for capturing and releasing CO₂ efficiently. This method could be scaled up and is similar to efforts by other companies. Recent studies suggest that using warehouse automation systems in DAC facilities could lower costs and improve scalability by making equipment handling and maintenance more efficient.

Political discourse

In the United States, there is disagreement between politicians and people who support environmental causes but are not part of any political group about Direct Air Capture (DAC). This disagreement focuses on whether DAC helps reduce the risks of climate change in a cost-effective way and whether it provides real economic benefits.

One major concern among climate activists is that DAC is seen as too expensive and not a priority compared to reducing emissions. Some believe it is used to keep the fossil fuel industry strong and continue pollution. The Stratos Project, which was bought by Occidental Petroleum for $1.1 billion, is owned by Occidental, an American oil company. Occidental purchased Carbon Engineering in 2023 for the same amount and sees carbon removal as a way to protect its industry. Jonathan Foley, who leads Project Drawdown (a plan to stop climate change), says DAC is a way for companies to make themselves look better without solving the real problem. The Consumer's Association of Penang believes DAC worsens the climate crisis and goes against the idea of fairness in addressing climate change.

A 2024 study looked at how people in the United States view DAC. It found that people who knew about DAC and worried about climate change had questions about the risks of using it. Many were worried that DAC could let companies keep polluting while making themselves look environmentally friendly. Others feared that fossil fuel companies might use DAC to create the illusion of helping the environment without real results.

Environmentalists also worry about the effects of DAC on the environment. Some are concerned about how DAC projects might harm air quality in certain communities. Others object to where DAC projects are built, as they often locate in poor areas, leading some to feel these communities are being treated unfairly.

Another study from 2024 looked at how people in the United States and the United Kingdom see DAC. It found that many believe DAC is not a true solution to climate change but a way to respond to it after the damage has already happened. People said DAC does not solve the main cause of emissions and instead helps the industries that cause the problem.

Political groups also question whether DAC can be developed and used widely. Similar technologies, like carbon capture and storage (CCS) and bioenergy with carbon capture and storage (BECCS), have faced public opposition and failed projects, which makes people doubt DAC’s success.

Some environmentalists say the $3.5 billion investment in DAC is risky because it could harm communities that are already struggling. The Institute of Policy Studies says this investment is dangerous because DAC might not work as promised, and if it fails, it could hurt these communities in new ways. Surveys show that people who oppose DAC have little trust in local governments and fossil fuel companies that fund DAC projects. Environmentalists also distrust the Bipartisan Infrastructure Law after a 2020 report found that 90% of tax credits for carbon capture were used without proof that carbon was captured. The IRS not sharing information about which companies benefit from DAC investments adds to people’s uncertainty.

A 2023 poll showed that 42% of Democrats strongly support DAC, 34% of independents support it, and only 28% of Republicans support it. Even though many environmentalists are against DAC, it has received support from both political parties in government.

The reason for bipartisan support is that DAC may help the environment and create economic benefits. Republicans believe DAC can bring jobs, more tax money, and economic growth to areas where DAC projects are built. Many fossil fuel companies, like ExxonMobil, also support DAC research. However, a 2024 survey found that Republicans and independents were less likely than Democrats to support building DAC projects in their communities or the United States.

Most discussions about DAC come from environmental activists. While Republicans and Democrats have different views on DAC, these differences mainly focus on how useful they think DAC is. Some, especially Democrats, see DAC as a way to fight global warming. Others, like Republicans, support DAC because it does not harm the economic interests of fossil fuel companies.

Direct air capture shortcomings

Bioenergy with carbon capture and storage (BECCS) has been questioned for several reasons. The main concerns are that the technology uses a lot of energy, needs large areas of land, and could allow carbon dioxide to escape back into the air. Environmentalists say BECCS is not a practical solution because the project might create more emissions than it removes. BECCS is suggested as a way to reduce carbon because it is believed that using bioenergy would not add more carbon to the atmosphere. However, this belief is incorrect because cutting down forests, logging, and using land for this technology might cancel out the carbon that the process removes. People who want to protect animals also worry that needing more land for BECCS could harm wildlife. Others say the danger of carbon dioxide leaking from storage sites is greater than the benefits if the technology works well. Carbon dioxide stored underground has a high chance of escaping, and a large leak could cause serious problems. "CO2 levels in the air could rise quickly, especially if a major leak happened at a storage site." Many people who are unsure about direct air capture (DAC) are worried about the possibility of CO2 leaks.

Direct air capture (DAC) uses a lot of energy. For example, it takes 5,000 kWh of electricity to capture 1 tonne of CO2. Most electricity grids produce a lot of carbon. In Australia, the grid produces 0.45 tonnes of CO2 for every megawatt-hour of electricity. This means a DAC plant in Australia would release more than 2 tonnes of CO2 for every tonne captured. In the UK, where the grid produces less carbon, the plant would capture as much CO2 as it emits. In Iceland, where the grid uses almost no carbon because it relies on renewable energy, the plant would release very little CO2.