Direct air carbon capture (DAC) is a technology enabling CO2 capture directly from the atmosphere, which plays an important role in the global net-zero emissions pathway. However, the feasibility of the technology has always been questioned due to its high energy consumption and its association environmental impacts. In addition, the real carbon removal efficiency of DAC technology needs to be carefully assessed though the methodology of life cycle assessment (LCA). The representative DAC technologies are summarized, among which the absorption method based on high temperature regeneration (L-DAC) and the adsorption method (S-DAC) DAC systems have high technology readiness level and are currently in the stage of commercial promotion. The research state of DAC LCA was then examined using the LCA framework, detailly from three aspects, including goals and scope, inventory analysis, impact assessment results and interpretation. Available studies show that both L-DAC and S-DAC technologies are capable of achieving net carbon removal, but the life cycle carbon removal efficiency of DAC technology ranges from about 10% to 95%, which is highly dependent on the system energy conditions. In the DAC life cycle carbon emissions process, the heat and power consumption of the system accounts for more than 80% of the GHG emissions, while the sorbent and absorber consumption in the DAC process and the plant construction account for less than 10% of the GHG emissions. In addition, the associated environmental impacts of DAC systems, such as life cycle water consumption, material consumption and land use, have also received attention. The initial estimate for the water consumption range of DAC technologies is 0–50 Gt/Gt CO2, and the utilization of renewable energy sources like solar and wind power to drive DAC systems would result in a large expansion of the land area used over its life cycle. Finally, the development trends and challenges of DAC life cycle assessment are sorted out, and the future research direction is prospected. At present, the research on life cycle environmental impact assessment for DAC systems is still in its infancy, lacking standardized analysis framework and data support from actual projects. It is also urgent to expand the life cycle assessment to the emerging DAC technologies and carry out dynamic life cycle assessment on DAC technologies as well as comparative analysis of DAC and other negative emission technologies. © 2023 China Coal Society. All rights reserved.
