For example, some adsorption materials may perform well in terms of CO 2 removal efficiency in dry environments, but are expected to perform poorly under high humidity (e.g., zeolites, K 2 CO 3 ). The lack of repeated cyclic exposure to capture and release conditions is a crucial obstacle to scale and is related to the current state of DAC: early stage of R&D, advanced RD&D comes from companies rather than academic groups and research organizations, and limited availability of test trials.