Understanding direct air capture (DAC)
Direct air capture is a technology that extracts CO2 directly from ambient air, unlike point-source capture which removes CO2 at concentrated emission sources. DAC is especially useful for achieving negative emissions and addressing historical emissions that are difficult to avoid.
How DAC works
- Air contact: large volumes of air are passed over chemical sorbents or filters that selectively bind CO2.
- Regeneration: the sorbent is heated or exposed to vacuum to release a concentrated CO2 stream.
- Compression and storage or use: the captured CO2 is compressed for geological storage (permanent removal) or used for products.
When DAC is valuable
- Negative emissions: to remove CO2 that has already been emitted, helping meet ambitious climate targets.
- Hard-to-abate sectors: complementing reductions in sectors where emissions are unavoidable.
- Offset and removal markets: as a credible method to deliver verified carbon removals when done with low-carbon energy and secure storage.
Strengths and limitations
- Strengths: DAC can be located away from emission sources, enabling placement near renewable energy or storage sites. It offers a scalable route to net-negative emissions if paired with permanent storage.
- Limitations: current DAC systems are energy-intensive and expensive compared with point-source capture. Cost reductions and scaling are required for broad deployment.
Environmental conditions and energy needs
Because atmospheric CO2 concentration is low (~420 ppm), DAC requires more energy to capture each ton of CO2 than capturing from concentrated streams. Using low-carbon heat and electricity is essential to ensure net carbon removal.
Outlook
DAC is likely to play a complementary role alongside emission reductions and point-source capture. Its importance grows as climate targets tighten and some historical emissions must be actively removed. Continued technology development, policy support, and investment are key to making DAC affordable at scale.