The solid sorbent and KOH BPMED FOAK scale is smaller than for the other two technologies leading to higher FOAK costs, yet similar costs at comparable scales. The smaller FOAK scale technologies incur a much higher FOAK cost as they cannot utilise economies of scale. However, these more modular technologies also exhibit more technological learning as there are greater opportunities to improve and reduce costs when producing such modules through mass production, and they undergo more doublings in installed capacity before a certain scale is reached. This leads to overlapping costs at similar scales across all four technologies. The downstream processing units of all the technologies, such as compression and condensation, are not inherently modular. Hence, they have a greater impact on the FOAK cost of the modular technologies, as economies of scale are not utilised. This can be observed in the ESI Figure , where the FOAK net removed cost for the most modular process, solid sorbent, is sensitive to the compressor capital cost. Co-located DAC systems could alleviate this if multiple plants share downstream processing units, which could be an opportunity to reduce the FOAK costs of (modular) DAC technologies.