Direct air capture facilities cost billions and require dedicated industrial infrastructure. They process ambient outdoor air with a CO₂ concentration of approximately 420 ppm. Meanwhile, every occupied building in the world circulates air at indoor concentrations of 600-1000+ ppm through existing HVAC systems. The infrastructure for carbon capture already exists — it circulates the air you are breathing right now.
A polyethylenimine-coated carbon nanofiber filter, sized like a standard HVAC HEPA filter, captures 92.1% of CO₂ passing through building ventilation. It regenerates by solar heating alone — the PEI material has high solar absorptivity, so exposing spent filters to sunlight releases the captured CO₂ for collection or sequestration. Net lifecycle efficiency, accounting for all manufacturing, transport, and disposal emissions: 92.1%.
Deployed in all buildings globally, such filters would eliminate 596 megatonnes CO₂ per year — equivalent to taking 130 million cars off the road. The filters slot into existing ductwork. No new construction, no new energy supply, no new infrastructure.
Building ventilation systems are energy consumers. This turns them into carbon sinks. The inversion is complete: the system that existed to condition indoor air for human comfort becomes, with a filter swap, a distributed network of carbon capture devices. The building was already doing the hard part — moving air past a surface. The filter just gives that airflow a second job.