Habits are hard to break. And that’s true of ourcenturies-old dependence on coal to heat andlight up our homes.

Burning fossil fuels such as coal and oil releasescarbon dioxide, the main culprit behind globalwarming. Carbon-free energy sources such aswind and solar power could combat this warm-ing, but they account for only 6 percent of thetotal energy consumed in the United States. Itwill be years before we move away from tradi-tional carbon-based energy sources and useenough clean energy to make a difference.

Until that happens, research has shown that wecould stabilize rising temperatures by removingcarbon dioxide from the atmosphere. ClimateDecision Making Center researchers are explor-ing a new and unique way to do that. It’s calledair capture, because the researchers use a chemi-cal to absorb CO2 directly from air.

Most current methods are designed to trap CO2from the gaseous waste products of powerplants and industries. But cars and trucks thatrun on gasoline are one of the biggest emittersof the harmful gas. Air capture can be used to capturethe CO2 emitted from these vehicles. Many expertshave predicted that clean vehicles powered by hydro-gen or electricity won’t become mainstream foranother two or three decades. “Air capture would atleast buy us time to transition to carbon-free vehicles,”says Joshuah Stolaroff, a doctoral student working onthe CDMC project.

Stolaroff, along with Professors David Keith and GregLowry have developed an experimental air capturesystem in the laboratory that uses sodium hydroxide asa sorbant, a chemical that absorbs gas, in this case CO2from air. A solution of the sorbant is sprayed througha reaction chamber. These droplets react with air andremove carbon dioxide. The resulting solution is

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New air capture methodcould reduce the harmfuleffects of carbon dioxideemissions from vehicles

CLIMATE DECISION MAKING CENTERCarnegie Mellon University

The towering, two-stories high prototype setupof the CDMC’s carbon dioxide air capture system

at the University of Calgary, Canada

The Climate Decision Making Center (CDMC) is an interdisciplinary collaboration between scien-tists at eight research institutions spanning the U.S., Canada and Germany. The center is anchored in theDepartment of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA. It is fundedby the National Science Foundation and was formed to develop and demonstrate a set of new decisionanalysis tools for addressing problems which involve high, and often irreducible levels of uncertainty.

chemically treated to separate the CO2, which iscompressed for storage, and the sodium hydroxide,which is reused. The researchers have built a 21 feettall prototype system that they’re testing at the Univer-sity of Calgary in Canada.

A real system would be even bigger—an open towerabout 390 feet (120 meters) high and about 330 feet(100 meters) in diameter. The sorbant would besprayed from the topwhile air is blown downthrough it. The chemicalreactions would be thesame as those in the lab.

All the chemicals involvedin this design are inexpen-sive, abundant andrelatively benign, saysStolaroff. The processesare well understoodbecause they are used inchemical manufacturingand the pulp and paperindustry, so the systemcan be made with existingtechnology. It could bemade larger in order to capture a significant fractionof CO2 emissions, he adds.

An important advantage of the air capture system isthat it removes the need for expensive carbon dioxidetransportation. Typical carbon capture plans for powerplants involve separating CO2 from flue gas—the gasmixture resulting from burning fuels—compressing it,and transporting it in pipelines to a storage site, whereit can be stored safely in the ground or in containers.

But the air capture system could sit anywhere,Stolaroff says, ideally right next to a storage site,

absorbing CO2 from air and putting it away, since thegas has nearly the same concentration around theglobe. “You could, for instance, put all the towers inAntarctica and capture the entire world’s emissions,”he says.

Stolaroff doesn’t believe that his system will replacecarbon dioxide capture from stationary sources suchas power plants. It would help with vehicle emissions,

and in addition, it couldbe ramped up in caseglobal warming turns outto be more disastrousthan we have expected itto be and we want toattack the problem morequickly.

The researchers estimatethat the system will costupwards of $240 forevery ton of carbon thatit removes. This is muchhigher than the currentand potential future taxfor carbon emissions. Butit could be much smaller

than “the costs of other strategies that people areserious about, like hydrogen-fueled cars and solar PV,”Stolaroff says.

And there’s no reason why air capture couldn’t beimproved, using a new material or a new process onexisting materials, he adds. “There is every reason toexpect that with time and a modest research invest-ment, the system could be much cheaper,” he says.

The prototype air capture system could be the firststep towards immediate carbon dioxide reduction, aswe slowly adapt to cleaner energy sources.

Cars spit out carbon dioxide, which causesglobal warming. The air capture system

will help absorb this gas.