Georgia Tech's bank tube–inspired direct air capture system.
Candler Hobbs, Georgia Institute of Technology Georgia Tech's bank tube–inspired direct air capture system.

While the built environment has thus far been a significant source of carbon emissions, it should now serve as a primary means of carbon drawdown. The use of carbon-storing materials to construct buildings, and the means to augment existing structures’ expansive combined surface area with carbon capture technologies, represent promising approaches to transform the constructed landscape into a carbon sink.

Such strategies are not optional. As the magnitude of our greenhouse gas problem increases, it is clear that mitigation alone will not suffice to meet global CO2 emissions targets. According to the Intergovernmental Panel on Climate Change, carbon capture and storage is “a critical decarbonization strategy in most mitigation pathways.” In other words, CCS has become a necessary method for addressing the climate crisis.

The architecture, engineering, and construction industry has focused primarily on embodied carbon, or carbon stored pre-construction. The popularity of mass timber, for example, is primarily due to the significant amount of carbon sequestered in wood (approximately half of the material’s weight), which enables it to outshine concrete and steel in this aspect of environmental performance. Operational carbon capture and storage—or CCS performed throughout a building’s use—should also be considered a fundamental part of the drawdown toolkit. Although this is a less-developed strategy, several emerging technologies are worth noting for future incorporation in design and construction.

These technologies represent an approach called direct air carbon capture and storage. Unlike traditional CCS methods that require proximity to the source of carbon emissions, DACCS can pull carbon directly from the ambient air. One technique, devised by chemical engineers at Georgia Tech, utilizes pneumatic tube modules similar to those seen at drive-through banks. The technology employs carbon-coated fiber strands that attract CO2 from ambient wind flow without the use of noisy fans. The strands are then heated to recapture the carbon, now contained within the tube, to be stored or used to make industrial fuels or chemicals.

As these technologies develop further, DACCS will offer a welcome supplemental function in building envelope and infrastructural applications and, just like forests, will continuously remove carbon from the ambient air.

A Northwestern University team of researchers has developed another ambient air-capture strategy that utilizes the so-called “moisture-swing technique.” This approach employs carbonate and phosphate ions to capture and release carbon based on relative humidity. CO2 is captured when the humidity level is low and released when it is high. “We liked moisture-swing carbon capture because it doesn't have a defined energy cost,” Benjamin Shindel, a Ph.D. student on the team, told Northwestern. “Even though there’s some amount of energy required to humidify a volume of air, ideally you could get humidity for free, energetically, by relying on an environment that has natural dry and wet reservoirs of air close together.” The researchers are currently experimenting with coating a metal-filtering sponge they developed previously with the carbon-capturing chemicals.

Scientists at the University of California, Riverside have developed a method to capture carbon passively using novel materials. Two compounds, MXene and MBene, discovered by Drexel University scientists, are superthin crystalline lattices consisting of just a few atoms in thickness. The UC Riverside engineers identified the high carbon absorption potential of these materials, given their significant surface area and ability to be tuned for carbon selectivity with a process the researchers have termed “interlayer distance engineering.” The team proposes combining the lattices’ CO2 absorption functionality with active, long-term carbon sequestration technologies like Climeworks.

In the open access letter “Can future cities grow a carbon storage equal to forests?” researchers at Aalto University in Finland speculate about the built environment’s capacity as a global carbon sink. Employing a new metric called the CS (carbon storage) Factor, the team estimated that a third of anticipated residential construction in the Uusimaa region of Finland could store an equivalent amount of carbon as forested areas. This finding is based on the carbon sequestration potential of the wood used in contemporary residential buildings.

While this determination reinforces the measurable advantage of embodied carbon in timber construction, wood buildings alone cannot be relied upon to sequester the amount of CO2 needed to attain world climate goals. One reason is that timber resources are not uniformly distributed, and “wooden construction should only be considered as a viable technology in regions that have access to sustainable forest management practices,” the researchers argue. Thus, in addition to the carbon sequestered in wood, direct air carbon capture and storage can play a significant role in meeting drawdown aims. As these technologies develop further, DACCS will offer a welcome supplemental function in building envelope and infrastructural applications and, just like forests, will continuously remove carbon from the ambient air.

The views and conclusions from this author are not necessarily those of ARCHITECT magazine or of The American Institute of Architects.

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