Economically viable geological CO2 storage from direct air capture has critical threshold of 70% CO2 concentration.

Direct Air Capture (DAC), a key component of Carbon Capture and Storage (CCS), has been widely studied. However, its large-scale deployment is hindered by the high energy cost of purifying captured CO₂. Using impure CO₂ can reduce energy consumption and overall costs, but it also lowers storage efficiency. This work employs molecular dynamics simulations to examine storage efficiency by analyzing the impurity systems' density across a wide temperature and pressure range. The results indicate a strong similarity between the density changes at the macroscopic level and the Van der Waals interaction changes at the molecular level. Additionally, the Normalized Storage Efficiency caused by Impurities (NSEI) is proposed, which can be used for storage potential and cost evaluation. A detailed NSEI analysis suggests that CO₂ concentration should reach at least 70% to achieve economically viable storage. This finding provides practical guidance for DAC capture system design and impurity CCS project planning.