A recent Communications Engineering study has identified a clear economic benchmark for storing carbon dioxide underground: the captured CO2 must be at least 70% pure.
Below this level, the cost of compression, transport, and injection rises sharply, making large-scale geological storage impractical.
Direct air capture (DAC) technologies often produce CO2 streams mixed with nitrogen, oxygen, and other impurities. Researchers found that diluted streams require far more energy to reach the supercritical state needed for secure storage, and impurities can increase leakage risks and monitoring costs.
Implications for Capture Technologies and Policy
For this study, the team combined system-level modeling with geological data from saline aquifers, depleted oil reservoirs, and basalt formations.
They concluded that meeting the 70% threshold may require extra purification stages for DAC methods such as sorbents, solvents, and membranes — potentially increasing costs but enabling long-term viability.
The study calls on policymakers to factor purity into CCS incentives, ensuring investments support technologies capable of meeting or surpassing the threshold. Industrial emitters and synthetic fuel producers may need to integrate centralized purification hubs or redesign processes to hit this target.
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Purity levels also vary in how they interact with storage sites, affecting reservoir chemistry and caprock stability. The authors suggest site-specific assessments adopt purity benchmarks to improve risk management and storage efficiency.
From an environmental standpoint, higher-purity CO2 reduces the extra energy needed for processing, lowering lifecycle emissions and unlocking significant cost savings at scale.
While the 70% standard sets a clear economic target, the study notes that improving reservoir monitoring and storage materials will remain critical for safe, long-term deployment.
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