直接空气碳捕集技术(DAC)能够从空气中直接移除二氧化碳，在全球净零排放路径中具有重要作用。但该技术的可行性始终受高能耗及其伴生环境影响的质疑，其实际碳移除效率需通过生命周期评价(LCA)方法评估。概述了现有代表性直接空气碳捕集技术，其中基于高温再生的溶液吸收法(L-DAC)和固体吸附的变温吸附法(S-DAC)DAC系统技术成熟度较高，目前在商业化推广阶段。依据生命周期评价框架，从目标和范围、清单分析、影响评价结果及解释3个方面对DAC生命周期评价研究现状进行分析和评述。L-DAC和S-DAC技术均能够实现净碳移除，但DAC系统的生命周期碳移除效率区间较大，为10%～95%，且极大程度上取决于系统的能耗及能量来源。在DAC生命周期碳排放过程中，系统的热力和电力消耗所造成的温室气体排放占比超过80%，DAC运行过程中所需吸附剂、吸收剂消耗以及工厂建设产生的温室气体排放占比均小于10%。此外，DAC系统的生命周期水耗、材料消耗及土地利用等伴生环境影响也受到关注，初步估算DAC技术的水耗范围在0～50 Gt/Gt CO2，利用光伏、风电等可再生能源驱动DAC系统会导致其生命周期土地利用面积大幅增加。最后，对DAC生命周期评价发展趋势与挑战进行了梳理并展望了未来研究方向。目前，针对DAC系统的生命周期环境影响评估研究仍处于起步阶段，缺乏标准化的分析框架及实际项目数据支撑，且亟需扩展针对新型DAC技术的生命周期评价，DAC动态生命周期评价以及DAC与其他负排放技术的对比分析研究。

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.