The extraction of CO₂ from ambient air, or direct air capture (DAC), is a crucial negative CO₂ emissions technology with great potential for contributing to the mitigation of global warming and climate change. However, nearly all published research on DAC has been conducted under indoor temperature conditions: 20 to 30 °C. In contrast, the future global implementation requires DAC to be operational across a wide expanse of geographical areas, in which the local temperatures can vary between −30 to 50 °C. Similarly, the absolute humidity can vary from ∼0 to 84 g/m³ in various locations. Due to the massive amount of air that would be processed, it may be impractical to preheat or dehumidify the air before the CO₂ separation. Therefore, it is important to develop DAC materials with good performance at realistic outdoor conditions, especially at sub-ambient conditions: −30 to 20 °C. In addition to material development, system-level studies at sub-ambient conditions are also needed for the DAC processes to reach optimal designs, which may be very different from those at ambient conditions. In this perspective article, we first assess the literature to identify the technical gaps that need to be filled for DAC to be applicable at realistic outdoor conditions. We then suggest additional research directions needed for DAC to be viable under varied conditions from the perspective of materials and system designs. For materials, we discuss the expected physical and chemical property changes for the sorbents when the temperature or humidity reaches extremes within their range, and how that will impact performance. Similarly, for system design, we indicate how varied conditions will impact performance and how these changes will impact process optimization.

从环境空气中提取 CO ₂或直接空气捕获 (DAC) 是一项关键的 CO ₂负排放技术，在缓解全球变暖和气候变化方面具有巨大潜力。然而，几乎所有已发表的 DAC 研究都是在室内温度条件下进行的：20 到 30 °C。相比之下，未来的全球实施要求 DAC 在广泛的地理区域内运行，其中局部温度可能在 -30 到 50 °C 之间变化。类似地，不同位置的绝对湿度可以从 ~0 到 84 g/m ³不等。由于将要处理大量空气，因此在 CO ₂之前预热或除湿空气可能是不切实际的分离。因此，开发在实际室外条件下具有良好性能的 DAC 材料非常重要，尤其是在低于环境条件下：-30 至 20 °C。除了材料开发之外，DAC 工艺还需要在亚环境条件下进行系统级研究，以达到最佳设计，这可能与环境条件下的设计非常不同。在这篇观点文章中，我们首先评估文献以确定 DAC 需要填补的技术差距，才能适用于现实的户外条件。然后，我们从材料和系统设计的角度建议 DAC 在不同条件下可行所需的其他研究方向。对于材料，我们讨论了当温度或湿度达到其范围内的极端值时吸附剂的预期物理和化学性质变化，以及这将如何影响性能。同样，对于系统设计，我们指出了不同的条件将如何影响性能以及这些变化将如何影响过程优化。