Direct Air Capture: Assessing Impacts to Enable Responsible Scaling

Highlights

Carbon removal will be needed, likely at a large scale, to limit global temperature rise to 1.5°C, which is necessary to avoid the worst impacts of climate change; direct air capture (DAC) is one carbon removal technology that is receiving growing investment and interest. Understanding its environmental and social impacts will be critical to scaling up equitably.
DAC plants are expected to have similar on-site resource usage impacts as other types of industrial infrastructure (e.g., land, energy, and water use), but significantly less on-site greenhouse gas (GHG) and conventional air pollutant emissions, particularly if powered by renewable energy. Responsible project design and regulation under the existing U.S. environmental regulatory framework can reduce adverse environmental impacts.
At the same time, because DAC is an emerging technology and its impacts vary by project, assessments will be needed on a project-by-project basis to understand expected environmental and social impacts in relation to alternatives or a no-action scenario.
Social impacts depend on the degree to which potentially impacted communities have access to information and can provide input into siting and project development decisions. Enactment of policies that require consideration of equity in DAC development will be necessary to avoid historical patterns of inequitable infrastructure siting.

Background

Limiting global warming to 1.5°C, as set out in the Paris Agreement, will require carbon dioxide (CO₂) removal from the atmosphere (IPCC 2018; NASEM 2019). This must be a complement to, not a substitute for, deep reductions of greenhouse gas (GHG) emissions. Carbon removal includes natural approaches, like planting trees, and technological approaches, like direct air capture (DAC), which uses chemicals to capture CO₂ from the air, and, when combined with geological storage or sequestration in a durable product, remove it permanently.

Among technological carbon removal options, DAC is attracting investment and interest. Its social and environmental impacts must be better understood, as with any new type of infrastructure. Today, more than a dozen DAC plants are operating worldwide, and plans are underway for two large-scale (0.5–1 million tonnes/megatons of carbon dioxide per year [MtCO₂/yr]) plants (Carbon Engineering 2021; Beuttler et al. 2019). These represent only a fraction of the up to 10 billion tonnes of CO₂ per year of carbon removal needed globally by midcentury across all carbon removal pathways (NASEM 2019). Given this expected large-scale need for carbon removal, it is important to understand DAC’s social and environmental impacts—both positive and negative. DAC’s nascency provides the opportunity to use this information and community engagement processes to counter historical patterns of inequitable energy and infrastructure siting to scale DAC responsibly from the outset (U.S. DOE 2021).

Key Findings

Ongoing impacts of operating DAC plants will come from energy, land, and water use (for DAC plant and energy source), and chemical use for the sorbents and solvents that capture CO₂. For a project removing a million tonnes (Mt) of CO₂ per year, these impacts would be similar to those of other industrial infrastructure, except that DAC would produce little to no GHG and air pollutant emissions on-site. DAC has siting flexibility, so it can be placed in locations that minimize impacts to people and the environment, for example, in climates that reduce water usage or on marginal land.

Energy: Using renewables would avoid on-site emissions of GHGs or air pollutants but would be relatively land intensive, while using natural gas with carbon capture would require much less land but would produce small amounts of GHGs and air pollutants and may be less acceptable to some communities.
Land: At a million tonne scale, solvent DAC plants (excluding energy sources) require roughly 0.4 square kilometers (km²) per plant while sorbent plants require 0.5 km² (Carbon Engineering 2020; Uzor 2022). By comparison, around 860 km² of forest is required to capture one million tonnes of CO₂ in the United States (Cook-Patton et al. 2020). Land area for energy resources would increase the footprint by 34 km² or 66 km² for solar and wind, respectively, at a million tonne scale. This land area could be used for other purposes, however, like grazing animals under wind turbines. In some cases, wind energy could be sited offshore to eliminate land use.
Water: Water usage is comparable to other industrial uses (Gerbens-Leenes et al. 2018). Locating solvent plants in cool, wet climates can reduce water usage; for sorbent plants, new variations in the technology can make plants net water producers in some locations.
Chemicals: On-site impacts of DAC chemical usage are expected to be minimal. Solvent DAC plants would release small amounts of solvent aerosols into the environment, but the amount is below the regulated limit (0.2 milligrams/cubic meter [mg/m³] or around 10 percent of the limit). Sorbents used in DAC plants degrade, but these degradation products, including ammonia, would likely be sequestered with the captured CO₂ and not released into the environment. Workplace use of chemicals always poses a non-zero risk, but chemical use in DAC plants would not be expected to be meaningfully different from use in other industrial applications, for which workplace handling guidelines mitigate risks.

Scaling up today’s DAC systems will require expanded production of some chemicals. Reaching the half billion tonnes (0.5 gigatons [Gt]) of technological carbon removal outlined in the U.S. Long-Term Strategy, if it were met entirely with DAC (half sorbent, half solvent capacity), would use around a little more than one-third of today’s global sorbent chemical production, the supply chain for which is still in development. Solvent DAC would use around one-fifth of today’s solvent production; scaling up solvent use is not expected to limit DAC deployment at a gigaton scale (McQueen, Gomes, et al. 2021). These amounts are based on sorbents and solvents used in commercially ready DAC systems today—the types and amounts of these chemicals will differ as DAC technology advances.

DAC scale-up will require expanding energy infrastructure to avoid competition with other uses for renewables. Based on today’s technologies, at a 1 MtCO₂/year scale, a sorbent plant requires an estimated 270 megawatts (MW) of power, and a solvent plant requires an estimated 280 MW of power (Keith et al. 2018; Beuttler et al. 2019).¹ With current technology, solvent plants use natural gas to provide high-temperature heat, whereas sorbent plants can use low-temperature heat from renewable energy or waste heat sources. DAC at 0.5 Gt scale would use around 4.4 percent of 2020’s primary energy supply and around 3.8 percent of 2050’s projected primary energy supply (U.S. EIA 2021).² New energy infrastructure would have upstream impacts associated with the materials supply chain and could impact ecosystems where sited, akin to building energy for non-DAC purposes.

DAC plants will need cement, steel, and other materials for construction, as will new energy infrastructure to power the plants. DAC scale-up would increase demand for materials that are already produced at a multimillion tonne scale in the United States, so near-term demand growth would generally be incremental. DAC at 0.5 Gt scale would use around 1–3 percent of current U.S. concrete and steel production each year. Scaling up materials production would also increase GHG and pollution impacts where those facilities are sited; reducing these materials’ supply chain impacts will require broader efforts from industry and government. DAC plants may also use low-carbon cement and steel alternatives.

A significant social impact of DAC is expected to be job creation, both on-site to operate the plant and elsewhere associated with manufacturing components and infrastructure. Other benefits could include financial compensation through pore space royalties or benefits codified through community benefit agreements. More work is needed to identify potential benefits and address community needs on a project-by-project basis. Potential social impacts are entwined with environmental impacts and include construction activity, increased traffic, and land use change, which will vary by project.

Since DAC is a new technology that is largely unfamiliar to the public and will require new infrastructure, investing in inclusive community engagement will be critical to responsible scaling. Community engagement should inform equitable decision-making around siting and project development and could help build understanding of DAC. Community engagement can also help maximize community and societal benefits and minimize negative impacts. These efforts my require additional resources but would help lay the groundwork for a more equitable and successful long-term scale-up.

Federal and subnational governments can support equitably scaling DAC through policies, and private sector actors can establish demand-side environmental and equity guardrails. The federal government can invest in foundational research, design, and demonstration; ensure that DAC is appropriately regulated under existing federal regulatory frameworks; and require social and environmental impact assessments (EIAs) and robust community engagement as a precondition to accessing federal funds. State and local governments can enact policies that enable zoning, planning, and permitting powers to support equitable DAC siting and development. In addition to policy guidance, carbon credit–certification programs can incorporate social and environmental impact criteria that must be met before DAC-generated carbon credits can be sold in voluntary markets.

These findings are preliminary as data are not comprehensive and DAC technology is evolving and improving. Data on the environmental impacts of different DAC and energy configurations in various locations will be needed to better understand impacts on a project-specific basis.

About This Working Paper

This paper builds on earlier WRI work on carbon removal—CarbonShot: Federal Policy Options for Carbon Removal in the United States—which identified the likely need for DAC in the United States. It analyzes the expected environmental impacts of building and operating DAC plants in the United States and provides considerations related to decision-making and DAC siting. It was written in collaboration between World Resources Institute and the University of Pennsylvania and is intended to inform policy and stakeholder discussions on DAC scale-up in the United States and to spur further research.

To avoid the worst impacts of climate change, global average temperature rise needs to be limited to 1.5°C, as outlined in the Paris Agreement. This means reaching net-zero carbon dioxide (CO₂) emissions globally by midcentury (IPCC 2018). The United States has committed to go further: net-zero across all greenhouse gas (GHG) emissions by 2050 (U.S. Department of State 2021). While emissions reduction is top priority, it will not be enough to meet global temperature goals; the IPCC (2018) indicates that all pathways that limit global warming to 1.5°C require carbon dioxide removal (CDR) to some extent. Large-scale carbon removal would reduce atmospheric CO₂ concentrations and neutralize emissions in sectors that are difficult-to-decarbonize by midcentury, like aviation and shipping (IPCC 2018; NASEM 2019).

Carbon removal includes both natural and technological approaches that pull CO₂ directly from the air and differs from carbon capture and storage (CCS), which captures CO₂ at sources like cement plants. Nature-based approaches include tree planting and agricultural practices that increase carbon in soil and plant biomass, while technological approaches accelerate natural carbon cycles or directly remove CO₂ from the air. Direct air capture (DAC) is a technological approach that removes CO₂ from the atmosphere through reactions with certain chemicals, and can be paired with several sequestration methods. Nature-based carbon removal strategies can be scaled up given sufficient workforce and infrastructure (Fargione et al. 2021), but their potential will be constrained by land availability, sensitivity to a changing climate, and the need to maintain ecological integrity (Seddon et al. 2020). To minimize risks, a robust carbon removal portfolio should include a variety of natural and technological approaches, including DAC (Mulligan et al. 2020).

Compared to other carbon removal approaches, DAC has several benefits: it can be configured to use relatively small amounts of land; it can be sited relatively flexibly within practical constraints, so it does not compete with agricultural or other productive land uses; and it offers quantifiable and permanent CO₂ removal when combined with geological sequestration or used in durable products (e.g., concrete). These are some of the reasons it has received attention and increasing investment in the past few years.

The amount of technological and natural carbon removal needed will depend on the speed at which countries are able to decarbonize. The International Panel on Climate Change (IPCC) and the National Academies of Sciences, Engineering, and Medicine (NASEM) both suggest the potential need for up to 10 billion tonnes (gigatons [Gt]) of carbon removal per year globally by 2050 to stay below 1.5°C warming (IPCC 2018; NASEM 2019). The United States’ Long-Term Strategy (LTS) points to around 0.5 GtCO₂/year of carbon removal domestically by 2050 (roughly 8 percent of U.S. emissions in 2019) across all technological solutions (U.S. Department of State 2021; U.S. EPA 2021b). If mitigation efforts are less successful or nature-based solutions fall below potential, both the amount of technological carbon removal and its deployment rate would need to increase. Regardless of the ultimate amount of DAC, near-term investment and scaling are needed to make future large-scale DAC feasible (Hanna et al. 2021; Repmann et al. 2021).

Estimating carbon removal needs is typically based on Integrated Assessment Models (IAMs), which use economics as a basis to identify the most impactful, low-cost mitigation pathways but are not designed to account for social or local impacts or externalities and may not include new technologies. This paper seeks to complement assessments that prioritize cost by considering environmental and social impacts of DAC that could also help inform scale-up levels and approaches.

How DAC Works

In a DAC plant, air is exposed to a capture medium—a chemical that selectively binds CO₂ while allowing the other components to pass through. Applying energy, typically as heat, releases the CO₂ into a contained environment and regenerates the capture medium for subsequent rounds of capture. Ideally, a zero- or low-carbon energy source, such as renewable energy or natural gas with carbon capture, produces that heat. After the CO₂ is released, it can be transported for permanent underground storage or used in products ranging from beverages to concrete.

There are currently two leading DAC technologies, determined by capture media: solvent and sorbent plants (Figure 1). Solvent plants use a liquid solvent (e.g., dilute potassium hydroxide [KOH]) to absorb CO₂ as ambient air passes through. The dissolved CO₂ then binds with calcium to form a stable solid mineral. CO₂ is released through application of high-temperature heat (900°C/ 1,652°F), which is achieved today with natural gas, but could be achieved through other options like clean hydrogen in the future. Solvent-type plants are built at larger scale today because of cost advantages specific to the plants’ components. Sorbent plants use a solid sorbent as the capture medium, which functions like a filter, selectively binding CO₂ and allowing other components to pass through. Sorbent plants use low-temperature heat to release the CO₂ from the capture medium—80–120°C (176–248°F), which allows use of renewable energy and waste heat—and are built in a more modular fashion with many smaller repeating units.

DAC is a nascent industry: the largest commercial plant in operation is Climeworks’ Orca plant in Iceland, which came online in September 2021 and uses geothermal energy to remove 4,000 tonnes of carbon dioxide per year (tCO₂/year) (Figure 2). Additionally, the first million tonne/megaton (Mt) scale plant is in development in the United States, with another planned for Scotland, and there are over a dozen smaller-scale DAC plants operating globally already (Beuttler et al. 2019; Carbon Engineering 2021).

American public officials have stated DAC’s importance in achieving global climate goals by providing $3.5 billion for DAC hubs—locations where DAC will be able to store or use at least 1 MtCO₂/year—in the 2021 Infrastructure Investment and Jobs Act (IIJA, also known as the Bipartisan Infrastructure Law) (U.S. Senate 2021). Due to DAC’s commercial immaturity, operational data are limited or in some cases nonexistent, and technologies and processes are expected to change as more plants are deployed. New approaches are emerging that can shift or minimize resource intensity, like all-electric DAC configurations or sorbents with longer life times. For these reasons, this analysis is preliminary and conclusions may change as technologies develop and more data become available.

Scope and Methods

This assessment considers a range of impacts, beyond DAC’s intended goal of carbon removal, from building and operating DAC plants—both on-site and in the supply chain—including pollutants, use of land, energy, and water, and benefits like job creation. These impacts are associated with a range of activities in the construction and operation of DAC plants (Figure 3).

Impacts were assessed based on a literature review of papers from peer-reviewed, government, and industry sources. Policy and procedural recommendations were assembled from a broad review of environmental justice; community engagement; and just transition literature from academic sources, and from community organizations, nongovernmental organizations (NGOs), and government sources. Peer-reviewed papers specifically examining the environmental impacts of DAC are few (e.g., Deutz and Bardow 2021; Terlouw et al. 2021; Madhu et al. 2021), given the nascency of the technology.

We discuss the broad categories of impacts expected at the plant level (capturing 1 MtCO₂/year) and at a larger potential scale by 2050 (0.5 GtCO₂/year, as outlined in the U.S. LTS, or 500 1-Mt plants), using the previous sources as well as those specific to the impacts of each activity. We assess impacts in relation to today’s leading DAC technologies.

While impacts of end uses and transportation of captured CO₂, such as CO₂ pipelines and geological sequestration, concern stakeholders and communities (Livermore Lab Foundation 2021; Batres et al. 2021) and must be considered in any build-out of DAC, they fit into a larger landscape of needs related to carbon management. As such, we do not consider these impacts in-depth and limit this analysis to elements specific to DAC or required for the construction and operation of DAC plants.

DAC Siting and Configuration

DAC can be sited flexibly within certain practical constraints. Siting decisions will likely be made by first identifying regions with land and energy availability and proximity to storage (Figure 4) and/or CO₂transportation infrastructure. First-generation plants may prioritize on-site use or storage of CO₂ or connecting to existing CO₂ pipelines to avoid the need for new transport infrastructure. After land, energy, and storage criteria are met, locations would be further narrowed by other environmental, community, regulatory, and economic considerations, including community willingness to host DAC plants and local zoning restrictions. Considerations like water scarcity, proximity to solvent/ sorbent producers, existing roads, and/or availability of disturbed or brownfield land, among others, could also influence siting location.

Importantly, DAC does not need to compete with productive or agricultural land uses and can be sited on marginal land. However, siting to maximize net CO₂ removal by, for example, colocating with low-carbon thermal energy resources, may impact local communities, ecosystems, or culturally significant lands. Although on-site pollutant emissions from DAC operation are expected to be small, other environmental and social impacts such as land and water use, noise associated with construction and plant operation, using fossil fuels, and the visual impact of the facility can add to existing burdens that some communities face. Low-income communities, and particularly low-income Black, Latino, and Indigenous communities, in both rural and urban areas, bear a higher burden of pollution and corresponding poor health outcomes than do higher-income, majority-white communities (Mohai et al. 2009), so it is vital that DAC siting decisions consider existing burdens on nearby communities.

Given that DAC plants are a new type of facility, it is particularly important that early projects are carefully evaluated through social and environmental impact assessments (EIAs) and use robust community engagement processesto involve impacted communities in decision-making.³ As communities are uniquely able to assess the relative risks and benefits of siting a DAC plant in their area, developers should proactively engage with communities as early as possible in the project time line to identify suitable sites and the technical and nontechnical aspects of the DAC configuration that meet communities’ needs.

DAC plants could be sited far from communities to avoid direct impacts on people or closer to reduce commuting time for workers, distance and cost to transport materials used at the facility, and transport-related emissions. Optimal distance from a community will differ by project and would need to consider trade-offs related to commute distance, land disturbance for road construction, and costs and distance to transport capture media and other materials that are used on an ongoing basis.

There may be additional ways to reduce or change impacts through DAC configuration and choice of energy resource, capture media, and other materials needs: research is ongoing to optimize processes and materials use. For example, Climeworks estimates that the GHG impact of construction materials will decrease by more than half from today’s 4,000 tonne carbon dioxide/year (tCO₂/year) plant to a future 100,000 tCO₂/year version, on a per tonne removed basis (Terlouw et al. 2021). Other improvements like extending sorbent lifetimes will also help reduce environmental impact. Low-carbon concrete and/or steel could also be used to reduce embodied emissions. All these choices carry trade-offs, depend on many factors (Figure 5), and will need to be determined on a project-by-project basis to reflect local circumstances and community needs.

Beyond the siting and energy impacts, DAC scale-up will increase materials demand, impacting communities where materials like steel, cement, and chemicals are produced. While project developers can prioritize materials with lower carbon intensity and environmental impact, reducing the climate and environmental impacts of materials and industrial production will require broader action from governments and regulators.

In this analysis, we categorize impacts according to their location and duration.

Location: Environmental impacts may be local or distributed. Local impacts occur either inside the “fence-line” of the DAC plant or in the host community, where impacts of the supply chain for construction materials, sorbent/solvent chemicals, or energy generation are often felt. Distributed impacts occur in regions outside of the host community, encompassing impacts from extended supply chain activities or energy (mainly electricity) procurement (Figure 6).

Duration: Some impacts are associated with one-time activities, like construction or decommissioning of the DAC plant. Others are associated with ongoing operations and occur continuously over a plant’s lifetime.

Here, impacts of individual DAC plants are assessed at a 1 MtCO₂/year capture scale, which is the size of the largest DAC plant in development today. Systemwide impacts are assessed at a 0.5 GtCO₂/year (500 MtCO₂/year) scale of DAC capacity, as this is the amount of technological carbon removal the U.S. LTS indicates could be needed by 2050 (U.S. Department of State 2021). While this scale could be smaller if other technological CDR approaches scale up, or larger if decarbonization is slow, it serves as an indication of possible DAC scale by 2050.

DAC facilities will be subject to the same environmental regulations that govern any new infrastructure or facility. They will need to apply for building and operating permits for the DAC plant, new energy resources, and CO₂ transport and storage infrastructure; perform an environmental impact analysis; and comply with applicable regulations for air, water, and toxic materials. Effective regulation depends on robust monitoring and enforcement, which is not always guaranteed. While individual DAC plants may emit little to no regulated air pollutants and their chemical losses to the environment may be below thresholds for reporting, large-scale DAC may require an assessment of whether existing regulatory frameworks are sufficient to address DAC plants as a new type of facility.

DAC Impacts: Local

The environmental impacts below are organized according to their proximity to the DAC plant site, beginning with impacts that are mostly within the plant “fence-line” and ending with those that affect adjacent lands, communities, and industries. Social impacts are considered in the following section.

Construction (one time)

Plant construction will create noise pollution, dust and particulate matter, soil and plant displacement, emissions from transportation of building materials, and potentially require building roads or housing for construction workers. Increased traffic through communities to DAC sites and presence of large numbers of construction workers would also affect communities. These impacts will likely compare with other types of infrastructure construction.

Visibility and noise (ongoing)

DAC plants and associated infrastructure may be in view of neighboring communities, which may be visually unappealing to residents and affect property values. The fans used in DAC plants produce some noise pollution, though this is minimal, particularly with appropriate distance from surrounding buildings.⁴

Energy demand (ongoing)

Today’s DAC technologies use nontrivial amounts of energy with roughly 80 percent for heat to regenerate capture media and 20 percent for electricity supply. Based on today’s technologies at a 1 MtCO₂/year scale, a sorbent plant requires an estimated 270 MW of power, and a solvent plant requires an estimated 280 MW of power for their total energy requirements (Keith et al. 2018; Beuttler et al. 2019).⁵ DAC at 0.5 GtCO₂/year would use around 4.4 percent of 2020’s primary energy supply and around 3.8 percent of 2050’s projected primary energy supply (U.S. EIA 2021).⁶

DAC scale-up will require expanding energy infrastructure and cost-benefit assessments of energy sources in different locations. DAC plants may be able to connect to the grid or use existing curtailed, stranded, or waste energy resources. However, connecting to the grid would shift impacts elsewhere, and curtailed, stranded, and waste energy would not be sufficient for large-scale DAC. Thus, this analysis considers new energy builds for DAC, which could be near the DAC plant or not. This assumption also helps avoid competition for renewables and means DAC companies have more control over the carbon intensity of their energy. Energy considerations for DAC include several complexities and possible energy sources beyond this analysis’ focus on comparison across prominent generation choices (solar, wind, geothermal, and natural gas).⁷

Energy carbon intensity is the main determinant of net climate impact of DAC (Deutz and Bardow 2021; Terlouw et al. 2021). However, when energy sources have zero ongoing/on-site emissions, as with wind or solar photovoltaic (PV), other aspects of the system like construction and sorbent production play a larger role in determining climate impact (Deutz and Bardow 2021). These renewable sources have other environmental and social impacts.

Solar PV and wind turbines do not emit GHGs or other air pollutants, but they can fragment ecosystems and disrupt habitats (UCS 2013a, 2013b), depending on how and where they are constructed. Integrating wind turbines and solar panels into grazing and farmland could reduce these impacts (Bergen 2020; McDonnell 2020), while offshore wind could also eliminate land use. Geothermal power would likely have similar ecosystem impacts, and, depending on the system, can produce some on-site emissions of sulfur dioxide (SO₂) and CO₂ (U.S. EIA 2020). Geothermal power has a relatively small surface footprint and can also share land use. Some projects have caused induced seismicity and land subsidence, but these can be avoided with appropriate siting, management, survey methods, and monitoring (U.S. DOE 2012; Sektiawan et al. 2016; Lowe 2012).

Powering DAC with natural gas requires capturing emissions to maximize net carbon removal (McQueen et al. 2021). To generate heat, the Carbon Engineering plant will combust natural gas in a high-oxygen environment, rather than normal air (Keith et al. 2018). This oxygen-firing system produces an exhaust stream of CO₂ and water, simplifying CO₂ separation from the flue gas (NETL n.d.). It also reduces nitrogen content, and thus emission of nitrogen oxides, which are of particular concern for human health. Oxygen-firing requires an air separation unit to separate oxygen from nitrogen in air, which is powered by electricity and uses around as much energy as the fans that move air over the contactor (0.3 gigajoules per tonne of carbon dioxide (GJ/tCO₂) (NASEM 2019). Solvent DAC plants could use natural gas or grid connection for their electricity needs. Natural gas would also require pipelines, for which natural gas leakage must be accounted, as well as upstream impacts from extraction.

Along with CO₂, DAC plants may also capture minimal amounts of criteria air pollutants, but not enough to make any meaningful difference in local air quality (Holmes 2021; Uzor 2021).

Land area: DAC plant and energy source (ongoing)

The amount of land used depends primarily on energy source (Table 1). At a megaton scale, solvent DAC plants (excluding energy sources) require roughly 0.4 km², while sorbent plants require 0.5 km² (Carbon Engineering 2020; Uzor 2022). By comparison, around 860 km² of forest is required to capture one megaton of CO₂ in the United States (Cook-Patton et al. 2020).

For some renewables, indirect land—land under solar panel arrays and between wind turbines—can be used for other purposes like agriculture, particularly for wind, where turbines only take up around 1 percent of total land footprint (Merrill 2021). At a 0.5 GtCO₂/year scale, DAC area needs range from 200 km² (roughly the size of Baltimore) to more than 33,000 km² (a bit smaller than the state of Indiana).

Table 1 | Total Land Areas for Different Combinations of DAC System Type and Energy Source

DAC system and energy source	DAC plant area (km²)	Energy source area (km²)	Total area for a 1 MtCO₂/yr plant (km²)	Area for 0.5 GtCO₂/yr of DAC capacity (km²)
Solvent: NG with CCS	0.4^a		0.4	200
Solvent: NG with CCS + solar PV	0.4	7.1	7.5	3,751
Solvent: NG with CCS + geothermal	0.4	1.5	1.9	927
Solvent: NG with CCS + wind	0.4	13.6	14.0	6,999
Sorbent: NG with CCS	0.5^b		0.5	250
Sorbent: solar	0.5	34.2	34.7	17,372
Sorbent: geothermal	0.5	7.0	7.5	3,757
Sorbent: wind	0.5	65.6	66.0	33,030

Notes: NG = Natural gas; CCS = Carbon capture and storage; PV = Photovoltaic; km² = square kilometers; MtCO₂/yr = Million tonnes of carbon dioxide per year; GtCO₂/yr = Billion tonnes of carbon dioxide per year. ^a Based on Carbon Engineering’s plant in development, which uses 100 acres (0.4 km²) for the DAC plant and energy infrastructure. ^b Assumes colocation of natural gas infrastructure with DAC plant.

Sources: Carbon Engineering 2020; Stevens et al. 2017; Beuttler et al. 2019; Keith et al. 2018; Uzor 2022; U.S. DOE n.d.

Solvent and sorbent use (ongoing)

Capture media (e.g., sorbents and solvents) are the materials in DAC plants that capture CO₂ from the air. DAC solvents are dilute mixtures of common chemicals, like potassium hydroxide (KOH), which is used today in soaps and fertilizers. While KOH is corrosive and can irritate skin and lungs if touched or inhaled, it can be safely used with appropriate workplace handling guidelines and safety precautions (CDC 2019a, 2019c). On-site impacts of solvents include aerosol formation and drift losses of 0.6 mg/m³ (Keith et al. 2018). Using demisters, which remove liquid droplets in vapor streams, can reduce this to 0.2 mg/m³ or lower (Holmes and Keith 2012). This is around 10 percent of the 2.0 mg/m³ limit set by the National Institute for Occupational Safety and Health (CDC 2019b), rendering it a likely minimal risk of operating solvent DAC plants.

Several sorbents can be used in DAC today. Each includes a reactive chemical that selectively binds CO₂, for example, an amine, attached to a material like alumina that provides structural support (Deutz and Bardow 2021). Because sorbents degrade over time and eventually need to be replaced, their lifetime is critical in determining their environmental impact. While sorbents have lifetimes of around three months to five years today (NASEM 2019), research is ongoing to extend lifetimes, which would reduce environmental impacts from frequently producing and disposing sorbents. Amine-based sorbents can produce ammonia and other byproducts as they degrade (European Environment Agency 2011; NASEM 2019). This degradation would happen primarily when heat is applied during sorbent regeneration, but because the system is closed to the environment during this phase to prevent CO₂ loss, sorbent byproducts would likely remain sequestered within the system and not be emitted in the exhaust stream. Capture media usage at a megaton scale plant is shown in Table 2.

Table 2 | Capture Media Use by 1 MtCO₂/yr DAC Systems

	Solid sorbent system (2-yr lifetime)	Solid sorbent system (5-yr lifetime)	Liquid solvent system (continuous circulation)
Materials use by DAC system at any given time	3,600 t sorbent	3,600 t sorbent	35,000 t KOH solution (82 t CaCO₃/day to disposal)
Materials consumed over plant lifetime (20 years)	36,000 t sorbent	14,400 t sorbent	6,845 t KOH drift losses 595,680 t CaCO₃ to disposal

Solid sorbent system

(2-yr lifetime)

Solid sorbent system (5-yr lifetime)

Liquid solvent system

(continuous circulation)

Materials use by DAC system at any given time

3,600 t sorbent

35,000 t KOH solution

(82 t CaCO₃/day to disposal)

Materials consumed over plant lifetime (20 years)

36,000 t sorbent

14,400 t sorbent

6,845 t KOH drift losses

595,680 t CaCO₃ to disposal

Notes: MtCO₂/yr = Million tonnes of carbon dioxide per year; t = Tonnes; mol = Mole; kg = kilograms; mg = Milligrams; m³= Cubic meters; KOH = Potassium hydroxide; CaCO₃ = Calcium carbonate; h = Hour. Sorbent assumptions: uptake of 1 mol CO₂/kg sorbent; cycle time 1 hour, 80% desorption efficiency (amount of CO₂ released from sorbent bed), and 92% uptime (operating 330 days/year). Solvent assumptions: 1.0 mol KOH solution, 0.2 mg KOH/m³ drift losses with demisters, and 3.4 t/h CaCO₃ disposal, and solvent not lost to drift can be reused at other facilities.

Sources: Keith et al. 2018; McQueen et al. 2020; Holmes and Keith 2012.

To understand the sorbent and solvent use impacts at a 0.5 GtCO₂/year scale, we use the current global annual production of ethanolamine, a precursor for the amine on silica sorbent, and global KOH production, which are around 2.5 Mt and 2.6 Mt, respectively (Deutz and Bardow 2021; Global Newswire 2021). Sorbent plants, at half of 0.5 GtCO₂/year capacity, would use around 37 percent of today’s global ethanolamine production (used today in detergents, pharmaceuticals, and other CO₂ scrubbing applications); and solvent plants, making up the other half of DAC capacity, would use around 19 percent of today’s KOH production. The supply chain for sorbents is still developing and would need to scale up to meet large-scale demand while increased solvent production is not likely to limit scale-up (McQueen et al. 2021).

Sorbent and solvent use will require transport into and out of communities, with the minimal but non-zero risk of spills or chemical contamination.

Water use (ongoing)

Both solvent and sorbent DAC plants use water in their capture processes, although some sorbent plants can, on net, produce water. For solvent plants, water use depends on solvent concentration and local temperature and humidity. More concentrated solvents use less water, as do lower temperatures and higher humidity (Keith et al. 2018; NASEM 2019) (Table 3). In Texas, where Carbon Engineering’s megaton plant is in development, water loss is expected to be roughly 4–6 tonnes of water per tonne of carbon dioxide (tH₂O/tCO₂), primarily from evaporation (Keith et al. 2018). As context, 6 tH₂O is about two-thirds the water usage of producing a tonne of steel and nine times that of producing a tonne of cement (Gerbens-Leenes et al. 2018). The solvent process does not produce a significant amount of wastewater, and on-site wastewater treatment is not anticipated (NASEM 2019).

For sorbent plants, steam can be used to regenerate the sorbent with around 1.6 tH₂O/tCO₂ lost to evaporation. Other types of sorbent plants use indirect heating with electricity and could be net water producers in cooler, wetter climates. For example, Climeworks’ technology can capture 0.8–2.0 tH₂O/tCO₂ (Fasihi et al. 2019).

Table 3 | Water Use by System and Climate

	Liquid solvent DAC system (water consumed/ MtCO₂ captured)	Solid sorbent DAC system
West Texas	~4–6 Mt water	1.6 Mt water/MtCO₂ lost to evaporation with steam regeneration 0.8–2.0 Mt water produced/MtCO₂ with indirect heating
Nevada	~6 Mt water
Oregon	~3 Mt water

Notes: MtCO₂ = Million tonnes of carbon dioxide; mol = Mole. Solvent plants assume a 2 mol solution with water use based on average temperature and humidity by location. For sorbent plants, data are unavailable to differentiate by temperature and humidity.

Sources: Keith et al. 2018; Fasihi et al. 2019.

Water is also needed for energy resources powering DAC. Thermal energy sources, like natural gas, can consume just under a million tonnes of water for the energy needed to capture a million tonnes of CO₂, primarily for cooling, and can harm local ecosystems if discharged at high temperatures (Macknick et al. 2011).

Water use may be a concern in water-scarce areas, where DAC plants could compete with agriculture, residential, or other water uses. DAC siting flexibility, however, can help avoid this, and siting in cooler and wetter climates can reduce net water use. Selecting energy sources with lower water requirements, like solar PV, could also avoid exacerbating water stress.

DAC Impacts: Distributed

Impacts from materials production and transportation would be distributed throughout the region or country, or materials could be imported.

Construction materials production and transport (one time)

Manufacturing the materials needed for plant construction and operation—primarily concrete and steel along with other materials like plastic, aluminum, and copper—will emit air pollution and cause other impacts near those production facilities. These impacts are not unique to DAC but need to be considered in high scale-up scenarios where materials needs would increase today’s production levels. While these emissions would be one time in reference to each DAC plant, they may be continuous with reference to the production facility, depending on the rate of DAC scale-up.

Nearly one hundred million tons of cement (the key ingredient in concrete) and steel are both produced per year in the United States. A megaton-scale DAC plant is expected to use up to 0.05 percent, 0.07 percent, and 0.4 percent of current U.S. production of concrete, steel, and polyvinyl chloride (PVC), respectively (USGS 2021a, 2021b). Reaching a 0.5 GtCO₂/year scale by 2050 would likely use around 1–3 percent of current U.S. production of concrete and steel and up to around 8 percent of current PVC production each year (assuming a linear scale-up from 10 Mt in 2030 to around 0.5 Gt in 2050) (Table 4). Large-scale deployment of DAC could cause marginal increases in emissions of CO₂ (unless captured), particulate matter, mercury, nitrogen oxides, carbon monoxide, sulfur oxides, and other pollutants associated with production of these materials and would be subject to Environmental Protection Agency (EPA) regulation. Despite EPA regulation, studies have shown that living in proximity to production facilities is linked to adverse health impacts—primarily respiratory diseases (Raffetti et al. 2019; Breugelmans et al. 2013).

Outside of general infrastructure requirements, there are two key differences in the materials needs of the solvent and sorbent approaches. The solvent approach led by Carbon Engineering uses a bed packed with PVC material, requiring 10,000–20,000 tonnes of PVC. The sorbent system does not have any additional needs for PVC outside of general use (e.g., plumbing, piping). Sorbent systems that use high vacuum conditions (e.g., Climeworks’ system) generally need more steel because they require thicker contactor walls.

Table 4 | Estimated Material Amounts by System Type and Scale

	Mt scale solvent plant	% annual material production used in any given year^a	Mt scale sorbent plant	% annual material production used in any given year^a
Concrete	250,000–275,000 t	≤ 2.4%	100,000–125,000 t	≤ 1%
Steel	20,000–30,000 t	≤ 1.3%	50,000–75,000 t	≤ 3.3%
Plastic (PVC)	10,000–20,000 t	≤ 8.2%	Negligible	Negligible

Notes: Mt = Million tonnes; t = tonnes; PVC = Polyvinyl chloride. Material amounts are proprietary; these are approximations based on preliminary project designs for leading systems, estimated capital designated for construction, dimensions publicly available and of similar constitution to a solid-fluid processing plant. U.S. concrete market based on 85 percent of the U.S. 89 Mt cement production used for concrete, with 15 percent cement content.

^a Percentages of total material production compare today’s production levels with estimated needs following a linear scale-up from 10 Mt in 2030 to 500 Mt in 2050.

Sources: USGS 2021a, 2021b; Hays 2021, for market sizes; PVC market size is for North America.

Solvent and sorbent manufacturing (ongoing)

Solvent DAC plants use common chemicals and materials produced today, like potassium hydroxide (KOH) and calcium carbonate (CaCO₃). KOH is produced with the energy-intensive chloralkali process, which uses around 2,500 kWh per tonne of material produced (DOE 2006). Emissions from this process would decline as the grid decarbonizes. The chloralkali process also produces harmful chlorine gas which could quickly saturate the merchant market as KOH production scales and would need to be safely managed. CaCO₃ is also used at a large scale today, in building materials like construction aggregate, and its main impacts would come from quarrying.

The types of sorbents used in DAC are like materials used in other types of carbon capture and use, common, but energy intensive, precursor chemicals like ammonia and ethylene oxide (Deutz and Bardow 2021). Sorbent end-of-life impacts would likely not be on-site, but at municipal incineration sites elsewhere, similar to disposal of sorbents used for potable water production; aluminum and silica could be recycled at rates up to 95 percent (Deutz and Bardow 2021).

Energy infrastructure (ongoing)

Impacts of energy infrastructure scale-up are not unique to DAC but must be considered since DAC scale-up could increase natural gas use and the significant renewable energy expansion already expected in 1.5°C scenarios. As above, we assume building out new renewable capacity to avoid competition for renewables; other infrastructure like transmission and energy storage would likely be needed as well.

Solar PV, wind, geothermal, and natural gas all have upstream impacts associated with producing materials like steel, concrete, glass, and aluminum. Solar PV and wind turbines, in particular, also require rarer metals like silver, iridium, and neodymium. Recent analysis finds that rare metal needs for solar and wind are expected to be more than tenfold current production amounts for many metals to meet a 2°C scenario—without considering concurrent DAC scale-up (World Bank 2017). As materials needs for decarbonization infrastructure grow, societal and environmental impacts of mining will also grow unless recycling rates increase and extraction practices improve. Ethical issues associated with mining are not unique to DAC, as many industries depend on mined materials, yet must be addressed if DAC is to scale equitably. Energy infrastructure also faces end-of-life concerns—for example, solar panel disposal in landfills can leak toxic chemicals like lead and cadmium (Xu et al. 2018).

In addition to materials considerations, upstream impacts of natural gas come predominantly from extraction (e.g., conventional recovery or hydraulic fracturing, which uses significant amounts of water and produces air and water pollution and noise) and methane leakage during transportation and storage, which is higher than average in the Permian Basin, located in the southwestern United States, where the first large-scale DAC project is in development (Fu et al. 2021; Zhang et al. 2020). New builds would have lower leakage rates, but expanding fossil fuel infrastructure could face stronger community opposition than adding renewable energy infrastructure. Early retiring natural gas plants could also be leveraged by converting them to combined heat and power plants with CCS to produce power during peak demand and then power DAC in off-hours. This approach would need to be considered on a case-by-case basis and only pursued when it is economically favorable and local communities are supportive.⁸

Communities can benefit financially from natural gas extraction, but may also experience negative impacts including competition for water, increased noise and traffic, and strains on existing infrastructure and services due to rapid economic growth (Ferrell and Sanders 2013). Additionally, the existing network of natural gas pipelines is concentrated more heavily in counties with higher levels of social vulnerability, placing a disproportionate environmental burden on these counties (Emanuel et al. 2021).

Box 1 | Defining Responsible DAC Scale-Up

Responsibly scaling DAC requires thoroughly assessing the economic, environmental, and social impacts of siting and operation and implementing actions to reduce potentially detrimental impacts and equitably increase benefits. We define “responsible DAC scale-up” as a process in which all actors engaged in building out DAC plants and supporting infrastructure:

where not already required by federal, state, or local law, conduct social impact assessments (SIA) and environmental impact assessments (EIA) prior to project site selection, and ensure that results are publicly available and accessible;
engage communities and assess ecological impacts to determine appropriate DAC siting locations;
establish contracts designed to equitably confer benefits to communities where DAC plants will be housed;
minimize negative environmental and community impacts in alignment with SIAs, EIAs, and community agreements.

To this end, we provide a preliminary assessment of potential environmental and social impacts of DAC scale-up. We also offer policy and procedural recommendations to provide an initial guide for responsible DAC scale-up and offer suggestions for research needs to inform technical aspects of DAC scale-up.

Source: Authors’ analysis.

OSHA specifies the maximum noise level for workplace fans is 85 decibels (dB) at 5 feet (ft) distance. Given sound drop off, the plant would need to be 500 ft from a residential neighborhood for sound to drop to 45 dB, which is considered maximum for nighttime noise level (WHO 1999).
Beuttler et al. (2019) reports energy needs for capturing 1 tCO₂ are expected to be 2,000 kWh in the long term, or 230 MW for 1 MtCO₂/yr. In the near term, we assume this value is closer to 2,400 kWh/tCO₂, or 270 MW for 1 MtCO₂/yr.
This comparison is only intended to contextualize scale using current, relatable numbers and is not a projection of the future market share.
Other energy sources could potentially help power DAC, including nuclear, hydropower, waste heat, and hydrogen.
With this strategy, DAC would not directly compete with decarbonizing the grid and could make use of surplus renewable electricity. After midcentury, these natural gas plants would reach the end of their life, and the deployment experience from using them would help reduce the cost of DAC. Energy sources for DAC could then be reevaluated and ideally shift to nonfossil resources. This would create a systems approach that leverages stranded natural gas assets, scales up renewables, and supports scaling up DAC over the next three decades.

Responsibly Scaling DAC

The process that determines DAC siting will, in part, decide who is impacted, positively or negatively. Opinions diverge on whether next-generation technologies like DAC will provide meaningful benefits for communities (White House 2021a; Batres et al. 2021), but the early DAC projects assessments for social and environmental impacts and benefits to communities will be essential to determining whether DAC will gain a “social license to operate” (Gunningham et al. 2004).

Since any climate intervention involving new infrastructure will have both positive and negative impacts, decision-makers and other stakeholders must understand the balance of those impacts and associated trade-offs. For example, although solar PV has drawbacks related to mining and disposal that need to be mitigated and managed, it is broadly accepted as a critical technology for decarbonization with net benefits.⁹ For DAC to be responsibly deployed at scale, thorough life-cycle analysis of its environmental and social impacts is needed on a project-by-project basis (Batres et al. 2021), along with identification of ways to minimize negative impacts.

Historically, building new infrastructure has not considered impacts holistically—for example, externalities of energy technologies such as water use and damage to culturally important sites have received less attention than air pollution and greenhouse gas emissions (Gies 2017). DAC’s nascency presents an opportunity to better understand and communicate potential impacts and cobenefits and prioritize inclusive decision-making.

We recognize that this approach can require effort, consideration, resources, and time, even as threats from climate change grow more urgent. However, it can lay the foundation for long-term success by establishing a shared understanding of project goals and parameters that allows for more efficient execution and helps avoid project delays due to community concern—a common result of late-stage community engagement.

Equitably Distributing Benefits

One critical aspect that will determine the equity and long-term viability of DAC scale-up is the assurance of benefits to communities where DAC plants and infrastructure are sited. There is an opportunity for DAC scale-up to not only remove CO₂ from the air but to offer benefits to communities and workers. Benefits could include high-paying jobs and training, local investment in CO₂ utilization, or potential financial benefits to owners of pore space where captured CO₂ is sequestered. DAC will likely be able to provide additional benefits to communities, but more research is needed to assess the types and magnitude of these benefits as more DAC plants are built and communities negotiate desired project benefits.

An assessment by the Rhodium Group (Larsen et al. 2020) estimates that 3,428 jobs (full-time, part-time, and seasonal) would be generated from building and operating a megaton-scale DAC plant. More than 3,000 of these are associated with plant investment, including equipment manufacturing, construction, engineering, and steel and cement manufacturing. The remainder are in plant operations, of which 278 are expected to be on-site for operations and maintenance. For context, there are 380 manufacturing jobs per establishment in the U.S. automobile industry, and an average of 46 and 28 jobs per generation facility in U.S. fossil fuel and geothermal electric power generation, respectively (BLS 2021). DAC operations jobs would be expected to last the lifetime of the plant, which is generally assumed to be 20 years (Fasihi et al. 2019), with high annual salaries expected, between $50,000 and $140,000, varying by industry (Larsen et al. 2020). If DAC plants are built continuously, jobs associated with plant investment could also be stable over time.

Residents of communities where DAC plants are sited could be employed in operations and maintenance and construction jobs, provided they receive skills training to fill these positions. Additional jobs would be created if captured CO₂ is stored or used locally. Other jobs, such as engineering, will probably not be on-site.

For DAC-related employment to benefit communities, jobs should pay at least family-sustaining wages, provide benefits such as health care and retirement, a safe and supportive work environment, and opportunities for career advancement and skill-building (Brett and Woelfel 2016).¹⁰ Once DAC reaches a large enough scale to offer widespread and long-term employment, job training programs with guaranteed employment could help ensure that local workers have the skills necessary to benefit from DAC-related job creation (Urban Sustainability Directors Network 2021). The construction and operation of DAC plants could engage workers from existing unions, offering the opportunity for collective bargaining.

A potential benefit could also come from pore space royalties, or payments to landowners where CO₂ is geologically stored. While there are ongoing legal debates about pore space ownership and rights are inconsistently applied in the United States, communities above or within a certain proximity of pore space or a monitored CO₂ plume could receive benefits. There is precedent for this in the oil and gas sector, where land and mineral rights are leased to oil and gas companies that pay royalties as high as 25 percent of their revenues (Gentile 2015). However, royalties to large landowners could inequitably exclude marginalized communities from benefiting, and inconsistent or unclear pore space rights cannot ensure smaller landowners are protected. Thus federal, state, and local governments should establish a framework that can assess who has rights to pore space, who might be affected by CO₂ injection, and how to equitably disburse benefits to affected parties (Johnson 2020).

A summary of environmental and social impacts of DAC is provided in Table 5.

Table 5 | Summary of DAC Impacts

Local impacts (environmental, social)	Magnitude of impact for 0.5 GtCO₂/yr DAC	Opportunity to manage impact through project design (straightforward, moderate, difficult)
Construction-related impacts^a (e.g., noise, particulate matter, influx of construction workers) (environmental, social)	Comparable to other types of infrastructure construction	Straightforward/Moderate
Visibility of facility, operational noise (environmental, social)	Dependent on project design and location in relation to people	Moderate
Increased traffic (environmental, social)	Dependent on project location; may be higher for solvent plants, which require more frequent addition of makeup solvent and calcium carbonate	Straightforward/Moderate
Energy demand to power DAC plants (environmental, social)	<5% of U.S. primary energy supply	Moderate/Difficult
Natural gas use for solvent plants (environmental, social)	Emissions of GHGs and nitrogen oxides (NOx) at much lower rates than natural gas plants without carbon capture	Straightforward (for sorbent plants that don’t need to use natural gas today) Difficult for solvent plants that use natural gas today
Land use: DAC plant (environmental, social)	200 km² for solvent plant 250 km² for sorbent plant	Moderate
Land use: energy source (environmental, social)	Variable depending on energy source: up to 33,000 km² for wind or 17,000 km² for solar, though both can be colocated with other land uses	Moderate/Difficult
Solvent and sorbent use (environmental)	On-site drift losses of solvents at 10 percent of regulated limit; no expected on-site impact of sorbent use	Moderate for solvents Straightforward for sorbents
Water use (environmental, social)	0–9 t H₂O/tCO₂ used for solvent plants depending on solvent concentration and local climate 1.6 t H₂O/tCO₂ used for steam regeneration sorbent plants, or up to 2 t water/ tCO₂produced for indirect heating regeneration	Straightforward/Moderate
Job creation (social)	278 expected jobs on-site for operations and maintenance for each Mt-scale plant, 139,000 jobs at a 0.5 Gt scale	Moderate
Job training (social)	Dependent on federal initiatives and negotiated benefit agreements	Moderate
Pore space royalties (social)	Precedent in the fossil fuel industry, but has not yet been demonstrated for DAC	Difficult
Additional community benefits possible via community benefit agreement	Dependent on negotiations between developer and community	Moderate
Distributed impacts (environmental, social)	Magnitude of impact for 0.5 GtCO₂/yr DAC	Opportunity to manage impact through project design (straightforward, moderate, difficult)
Reduction of atmospheric CO₂(environmental, social)	0.5 Gt scale DAC would result in a 63% increase over carbon removal by U.S. lands in 2019 (U.S. EPA 2021)	Moderate
Natural gas extraction and transportation (for plants powered with natural gas) (environmental, social)	Methane leakage rates depending on location, but average 2.3% in the United States; other environmental impacts are variable Social impacts are variable	Straightforward (for sorbent plants that don’t need to use natural gas today) Difficult for solvent plants that use natural gas today
Solvent and sorbent production (environmental)	Up to 37% increase in global ethanolamine production for sorbent manufacture; 19% increase in global KOH production for solvent manufacture (assuming scale-up is half solvent and half sorbent systems)	Moderate for sorbent Straightforward for solvent
Construction materials’ production and transport (environmental)	1–3% increase in annual production of cement and steel, up to 8% increase in annual PVC production	Straightforward/moderate; increase is incremental for most materials, but environmental impacts need to be managed
Energy infrastructure (environmental)	Dependent on energy source build-out and location	Moderate
Job creation (social)	More than 3,000 expected jobs in equipment manufacturing, construction, engineering, and steel and cement manufacturing	Moderate
Job training (social)	Variable	Moderate

Notes: GtCO₂/yr = Billion tonnes of carbon dioxide per year; GHGs = Greenhouse gases; NOx = Nitrogen oxides; km² = Square kilometers; H₂O = Water; Mt = Million tonnes; t = tonnes; KOH = Potassium hydroxide; PVC = Polyvinyl chloride.

^a Construction impacts are expected to be one time at each DAC site; other impacts are expected to be continuous.

Sources: Authors; primary sources in each section.

Equitable DAC scale-up will require federal and subnational governments and project developers to enact and adhere to good practices. The following recommendations are based on our analysis and focus on environmental and social impacts of DAC, rather than DAC scale-up overall.

Procedural Recommendations

Early DAC projects will be critical for building understanding of and trust in the technology and laying the groundwork for equitable community participation. While public engagement may not ensure acceptance of DAC, local stakeholders need to be engaged in siting decisions and planning processes to increase likelihood of buy-in and to secure locally desirable outcomes (Moser and Pike 2015).

Engaging communities early in planning decisions related to DAC can improve information flow and integration of diverse perspectives and ensure that communities receive project benefits. Community engagement and effective communication can also prevent perception of opaque, bureaucratic, or unilateral decision-making (Katsonis 2019). Robust documentation of engagement processes and outcomes will also help to address the current lack of research on potential social impacts of DAC (Forbes et al. 2009; Groundwork USA 2021). Procedural steps and legal agreements that enshrine community benefits in project planning should become standard practice in DAC development, including the following:

Social Impact Assessment (SIA): SIA is a process that assesses the intended and unintended social impacts of development. Conducting SIAs alongside environmental impact assessment prior to energy or infrastructure development projects ensures that project developers are considering options to mitigate adverse social impact from a project’s outset.
Community Benefits Agreement (CBA): CBAs are negotiated legal agreements between coalitions of community groups and project developers that guarantee community benefits in exchange for a community’s agreement not to oppose the project. Benefits secured through CBAs can include local hiring and procurement agreements, reduction of environmental impacts during construction and operation, and other benefits tailored to unique community needs.
Project Labor Agreement (PLA) and Community Workforce Agreement (CWA): A PLA is a negotiated agreement between construction companies or contractors and unions, agreeing to terms for the project. Projects with PLAs require contractors to use union labor and include no-strike agreements in exchange for dispute resolution agreements. CWAs are provisions within PLAs that require the contractor to hire a negotiated percentage of local, low-income, or other marginalized workers, collaborate with local organizations to provide job training programs, and agree to job quality specifications.

Federal Policy Recommendations

Federal action can play an outsized role in accelerating responsible deployment of DAC, and federally mandated practices can set the standard for future DAC development. Congress has already recognized the importance of funding DAC: appropriations for DAC research development and demonstration (RD&D) are increasing year-on-year, and the Infrastructure Investment and Jobs Act (IIJA) includes $3.5 billion for four megaton-scale DAC hubs. The Department of Energy has also recently launched Carbon Negative Shot, to decrease the cost of all forms of carbon removal to below $100/tCO₂. With these monumental investments in DAC, the federal government can ensure that public engagement, equity, and environmental justice are central to the development of all projects that receive federal funding. The Obama administration’s 2009 Executive Order 13502 set precedent for this by encouraging agencies to use project labor agreements for large construction projects (Carlock et al. 2021). More recently, the Biden administration’s 2021 Executive Order 14008 identified environmental justice and equity as key components of climate action across the federal government. The executive order directs agencies to create strategies for addressing environmental injustices, increase enforcement of environmental violations that disproportionately affect marginalized communities, and improve environmental monitoring and transparent reporting in frontline communities.

The following recommendations would build on existing federal momentum to enable responsible and equitable development and deployment of DAC. Other investments and initiatives will be needed to scale DAC, but these recommendations address federal action that could reduce the environmental impact of DAC and secure community benefits. The federal government could require that all DAC projects receiving federal funds do as follows:

Complete social and environmental assessments to identify siting locations that are socially and environmentally acceptable.
Engage in robust community engagement processes using skilled facilitators to ensure that all stakeholders, including marginalized community members, can choose to provide input on project development.
Encourage the use of legal agreements such as CBAs, PLAs, and CWAs, to ensure communities and workers can negotiate benefits they expect to receive.
Where possible, require that local labor and locally sourced, low-carbon material be used for construction and plant operation.
Where possible, require that DAC plants be powered by low- or zero-carbon energy sources and discourage the construction of new natural gas infrastructure.
Establish job training programs in communities adjacent to DAC plants and establish standards to ensure high-quality employment.

Federal agencies, including the Department of Energy, U.S. Geological Survey, and the Environmental Protection Agency can conduct RD&D to improve the technology and decrease the cost of DAC components as well as investigate methods to minimize and manage community and environmental impacts of DAC. Interagency research could prioritize the following:

Conduct thorough life-cycle assessments of DAC plants and supporting supply chain, transport, and storage infrastructure, to account for different geographies, energy sources, and DAC plant configurations. Research could also investigate potential impacts on human health and identify ways to decrease human and environmental impacts.
Evaluate existing regulatory frameworks to assess applicability to DAC plants and associated CO₂ transportation and sequestration. Where necessary, clarify the regulatory frameworks that will apply to DAC development.
Improve techniques for manufacturing DAC components, including sorbents and solvents, in cost-effective and environmentally friendly ways.
Identify methods of powering DAC plants that maximize energy efficiency and minimize negative environmental, community, and climate impacts.
Identify factors that should be used to determine optimal siting for DAC plants, including practical constraints and local community considerations.
Conduct social science research and polling to assess public perceptions of DAC and to better tailor communication and outreach.
Establish a DAC demonstration grants program that requires DAC projects to conduct community education and outreach and encourages creation of CBAs with communities where appropriate (Kosar et al. 2021).

Subnational Recommendations

State and local land use policies are already changing to make planning and siting of industrial projects more equitable. Widespread use of these policies can help address historical patterns of inequitable land use and unequal distributions of impacts and benefits and help create conditions to enable an equitable DAC scale-up.

Zoning and Planning: Local planning and policies can help counteract historical patterns of land use that concentrate locally unwanted land uses near and in communities that are low-income, Indigenous, or composed predominantly of people of color (Baptista 2019). Planning can also help address zoning driven by “NIMBYism (not-in-my-backyard-ism)” or an acceptance of the need for infrastructure, but opposition to building the infrastructure near the opponent’s home or community. Zoning influenced by NIMBYism can concentrate industrially zoned land and the resulting facilities in communities that have less political power to inform siting decisions and negotiate benefits. State, county, or city environmental justice initiatives can assemble advisory panels that provide input on planning and zoning decisions to ensure that health and economic impacts on marginalized communities are considered in planning decisions, and infrastructure that serves a public good, such as DAC, is distributed equitably.

Construction Permitting Processes: Cities, states, and counties can develop ordinances requiring new DAC facilities, infrastructure, and CO₂sequestration sites to complete environmental and environmental justice review processes to be eligible to receive building permits. Newark, New Jersey, set a precedent in passing an ordinance that requires developers seeking permits to disclose possible environmental impacts (Clean Water Action 2016). Related ordinances could similarly require community engagement and consultation prior to permits being granted.

Private Sector Recommendations: DAC project developers can prioritize procurement of lower-emission versions of materials like cement and steel, where possible, and can prioritize environmental impacts when selecting sorbents and solvents and their suppliers. DAC developers can also prioritize environmental impact, along with cost and efficiency, for in-house RD&D.

Because it has the potential to permanently remove carbon, DAC could provide verifiable carbon removals for emissions that are hard to abate in the near term (Joppa et al. 2021). If DAC projects provide carbon credits, credit certification programs could help to verify that DAC projects producing credits are developed in an environmentally and socially responsible way.

Leading voluntary carbon credit–verification programs already include thorough reviews of credit-producing projects to certify that credits are permanent and that projects do not harm communities or result in environmental degradation. While governmental oversight and regulation must be primarily responsible for enforcing the mitigation of environmental impact, verification programs may be able to help ensure that DAC projects follow good practices for community engagement and environmental impact mitigation beyond regulatory standards. DAC projects producing carbon credits should undergo review to verify that they have taken all possible actions to minimize negative environmental and community impact, and to ensure that benefits accrue to local communities. Project reviews conducted by carbon crediting programs could include the following criteria:

DAC developers should be required to provide transparent and regular reports on life-cycle environmental impacts of building and operating plants.
Developers should conduct community outreach and engagement processes consistent with the procedural recommendations above.
DAC plants should provide high-quality, long-term employment for their workers.

Analysis of commercially ready DAC systems indicates that on-site impacts are expected to be similar to those of industrial facilities of a comparable size, but with much lower GHGs and other air pollutant emissions. Solvent DAC plants would release some aerosolized chemical solvent but at much lower levels than is regulated; DAC plants powered with natural gas would also produce small amounts of CO₂ and nitrogen oxides (NOx) emissions, much lower than conventional natural gas plants. Most emissions related to DAC would happen off-site, related to production of materials needed to build and run the plant. DAC at a 0.5 GtCO₂/year scale is expected to have only incremental impacts on production of materials like cement and steel but would have substantial energy requirements and require scale-up of sorbent production. Because these impacts differ by project and will change as the technology improves, environmental and social impact assessments will be needed on a project-by-project basis.

This analysis offers a starting place to inform decision-makers in advancing an equitable and responsible scale-up of DAC to meet the expected carbon removal need. The federal government, states, and municipalities, and the private sector will need to collaboratively identify suitable locations for DAC and configurations that are best for each location, along with enacting policies that integrate equity considerations into DAC development. To enable an equitable DAC scale-up, stakeholders should play an early and central role in decision-making guiding DAC development to maximize benefits and minimize harm to communities hosting DAC plants. Early investments in community engagement and equitable policies and programs require time and resources, but are vital for the long-term success and equity of the DAC industry. DAC has the potential to become either an important technology to address climate change or a technology that does not gain widespread use due to lack of public acceptance. Careful development of DAC with environmental and social safeguards will enable effective and responsible DAC scale-up.

Capture media: Capture media are chemicals that can selectively bind to carbon dioxide gas in ambient air. Capture media can be liquid solvents or solid sorbents.

Carbon capture and use/storage (CCUS): CCUS captures emissions at the source to prevent them from entering the atmosphere (e.g., by capturing CO₂from a cement plant’s smokestack). Carbon capture is a form of mitigation.

Carbon removal: Approaches that pull carbon dioxide that has already been emitted out of the atmosphere. Natural carbon removal includes tree planting and agricultural approaches that add more carbon to the soil, and technological carbon removal includes engineered approaches like direct air capture that captures CO₂ via chemical reactions.

Community Benefit Agreement (CBA): A contractual agreement between a community and project developer that legally ensures community benefits in exchange for community support of a project.

Contactor: The contactor is the unit in a DAC plant that brings ambient air in contact with a solvent or sorbent.

Criteria air pollutants: The EPA sets National Ambient Air Quality Standards (NAAQS) for six common air pollutants in the United States, required by the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, lead, sulfur dioxide, and nitrogen dioxide.

Direct air capture (DAC): DAC pulls ambient air over a capture medium (e.g., solvent or sorbent) that chemically reacts with CO₂, removing it from the air. The captured carbon dioxide can then be stored underground or used in products.

Distributive impacts considerations: Considerations related to the distribution of negative and positive impacts that different DAC stakeholders experience, particularly in communities where DAC plants are sited.

Environmental justice: Environmental justice is the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income, with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies. This goal will be achieved when everyone enjoys,“[t]he same degree of protection from environmental and health hazards, and equal access to the decision-making process to have a healthy environment in which to live, learn, and work” (U.S. EPA 2021a).

Geologic storage: End-use option for captured CO₂ that involves injection into deep rock formations that trap and sequester it permanently. Carbon dioxide may also be injected into certain types of rock, where it reacts to form carbonates and is permanently stored in solid form.

Gt: Gigaton, or one billion tonnes. One Gt of CO₂ equivalent is roughly equivalent to emissions from the annual energy used in 120 million homes (U.S. EPA 2015).

High-/low-quality heat: The relative ease with which energy converts into mechanical energy; low-quality heat does not as easily convert to work because it is less concentrated and organized. Many sources of industrial waste heat are low quality and can serve the energy requirement for sorbent plants, whereas solvent plants require high-quality heat. Low- and high-quality heat are typically associated with low and high temperatures, respectively, but differ from temperature.

Mitigation: Mitigation activities avoid or reduce emissions going into the atmosphere (e.g., by replacing a coal power plant with wind turbines). Mitigation is distinct from carbon removal, which removes previously emitted CO₂.

Mt: Megaton, or one million tonnes; 1 Mt of CO₂ equivalent is roughly equivalent to emissions from the annual energy used in 120,000 homes (U.S. EPA 2015).

Oxygen-fired kiln (oxyfuel combustion): Natural gas can be combusted in a high-oxygen environment rather than air, which makes postcombustion capture of CO₂ easier since flue gas is predominantly water and CO₂.

Procedural considerations: These considerations enable stakeholders to participate and be involved in decision-making in a fair way around environmental matters (Clayton 2000), such as DAC plants. Such considerations will be particularly necessary in communities where DAC plants are sited.

Tonne: Metric ton.

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1Beuttler et al. (2019) reports energy needs for capturing 1 MtCO₂ are expected to be 2,000 kilowatt-hours (kWh) in the long term, or 230 megawatts (MW). In the near term, we assume this value is closer to 2,400 kWh, or 270 MW.
2This comparison is only intended to contextualize scale using current, relatable numbers and is not a projection of future market share.
3Community engagement resources include Forbes et al. 2009; Groundwork USA 2021; and Katsonis 2019.
4OSHA specifies the maximum noise level for workplace fans is 85 decibels (dB) at 5 feet (ft) distance. Given sound drop off, the plant would need to be 500 ft from a residential neighborhood for sound to drop to 45 dB, which is considered maximum for nighttime noise level (WHO 1999).
5Beuttler et al. (2019) reports energy needs for capturing 1 tCO₂ are expected to be 2,000 kWh in the long term, or 230 MW for 1 MtCO₂/yr. In the near term, we assume this value is closer to 2,400 kWh/tCO₂, or 270 MW for 1 MtCO₂/yr.
6This comparison is only intended to contextualize scale using current, relatable numbers and is not a projection of the future market share.
7Other energy sources could potentially help power DAC, including nuclear, hydropower, waste heat, and hydrogen.
8With this strategy, DAC would not directly compete with decarbonizing the grid and could make use of surplus renewable electricity. After midcentury, these natural gas plants would reach the end of their life, and the deployment experience from using them would help reduce the cost of DAC. Energy sources for DAC could then be reevaluated and ideally shift to nonfossil resources. This would create a systems approach that leverages stranded natural gas assets, scales up renewables, and supports scaling up DAC over the next three decades.
9Of note, the U.S. banned imports of products made with silicon from Xinjiang, China, where there is “reasonable” indication of use of forced labor (Kaplan et al. 2021).
10A family-sustaining wage is defined by the Massachusetts Institute of Technology (MIT) Living Wage Calculator as a wage that is higher than $22/hour.

The authors are grateful to numerous individuals who provided valuable input, feedback, and support to this work. We thank our external reviewers who have shared their expertise and insights: Adam Baylin-Stern, Holly Buck, Kel Coulson, Nicholas Eisenberger, Ruth Garcia, David Hawkins, Geoff Holmes, Ugbaad Kosar, Elise Lepine, Colin McCormick, Ben Rubin, Maxime Tronier, Simone Stewart, Louis Uzor, Frances Wang, and Caleb Woodall.

Thanks also goes to WRI colleagues for their thoughtful review, comments, insights, and guidance: Christina Deconcini, Karl Hausker, Jillian Neuberger, Carla Walker, and Debbie Weyl. We would especially like to thank Dan Lashof and Angela Anderson for their review and guidance.

While the contributions from reviewers are greatly appreciated, the views presented in this paper reflect those of the authors alone.

We also wish to thank Romain Warnault, Emily Matthews, Shazia Amin, Renee Pineda, Shannon Collins, and Rosie Ettenheim for editing, design, and production, and Carrie Dellesky for communications support.

This project was made possible through the generous funding from the Linden Trust for Conservation.

Katie Lebling is an associate in the U.S. Climate program at WRI. Her work focuses on technological carbon removal and industrial decarbonization in the United States.

Contact: katie.lebling@wri.org

Haley Leslie-Bole is an associate in the U.S. Climate program at WRI. Her work focuses on leveraging state and federal policy to increase the capacity of natural and working lands to sequester carbon. She also works to ensure that equity and community engagement are central to the carbon removal scale-up.

Contact: haley.leslie-bole@wri.org

Elizabeth Bridgwater is a research analyst in the U.S. Climate program at WRI. Her work focuses on carbon dioxide removal and U.S. subnational climate action.

Contact: elizabeth.bridgwater@wri.org

Zachary Byrum is an associate in the U.S. Climate program at WRI. His work focuses on policy options to scale up technological carbon removal solutions and industrial decarbonization in the United States.

Contact: zachary.byrum@wri.org

Peter Psarras is a research assistant professor in chemical and biomolecular engineering and energy policy at the School of Engineering and Applied Sciences and Weitzman School of Design at the University of Pennsylvania.

Contact: psarras@seas.upen.edu

World Resources Institute is a global research organization that turns big ideas into action at the nexus of environment, economic opportunity, and human well-being.

Our Challenge

Natural resources are at the foundation of economic opportunity and human wellbeing. But today, we are depleting Earth’s resources at rates that are not sustainable, endangering economies and people’s lives. People depend on clean water, fertile land, healthy forests, and a stable climate. Livable cities and clean energy are essential for a sustainable planet. We must address these urgent, global challenges this decade.

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Direct Air Capture: Assessing Impacts to Enable Responsible Scaling

Executive Summary

Highlights

Background

Key Findings

About This Working Paper

Introduction

How DAC Works

Scope and Methods

DAC Siting and Configuration

Expected Environmental Impacts of DAC Plants

DAC Impacts: Local

Construction (one time)

Visibility and noise (ongoing)

Energy demand (ongoing)

Land area: DAC plant and energy source (ongoing)

Solvent and sorbent use (ongoing)

Water use (ongoing)

DAC Impacts: Distributed

Construction materials production and transport (one time)

Solvent and sorbent manufacturing (ongoing)

Energy infrastructure (ongoing)

Responsible Scaling and Equitably Distributing Benefits

Responsibly Scaling DAC

Equitably Distributing Benefits

Policy and Procedural Recommendations

Procedural Recommendations

Federal Policy Recommendations

Subnational Recommendations

Conclusion

Glossary of Terms

References

Endnotes

Acknowledgments

About the Authors

About WRI