In a new study, scientists have explained for the first time the specific mechanism by which carbon dioxide (CO2) and water interact at the air-water interface. Christoph Schran and his group at the Cambridge University Cavendish Laboratory discovered something that was paradigm-changing. Yet they’re unpacking the intricate chemical processes that occur once CO2 is released into the atmosphere. Billions of tons of CO2 from human activities are released into the atmosphere each year, with serious impacts on climate and ocean chemistry.
The study also emphasizes that CO2 does not have to completely mix in solution for the reaction to occur. At the same time, it layers quickly into an active exchange process at the water’s surface. As a result, this action forms carbonic acid (H2CO3) through a remarkable “in-and-out” strategy. This fresh perspective may help improve existing models forecasting how the oceans will become more acidic and what that means for marine life.
The Mechanism of CO2 Hydration
The research team used enhanced sampling molecular simulations to investigate the interaction of CO2 with water. What does their research demonstrate about CO2 reactions in the oceans? It goes on to form carbonic acid, both due to its partial dissolution in the upper layer. Samuel G. H. Brookes, a key researcher in the study, describes this process succinctly:
“It is like, instead of diving deep into the water to react, CO₂ does a quick dip in the water, partially dissolving in the topmost layer of water where it can react to form carbonic acid. This acid species then returns to the surface and pops back out.” – Samuel Brookes
The mechanism they’ve proposed raises questions on the dynamics of CO2 reactions, which have long been assumed in the form of a bimolecular reaction style. These new models are important as traditional models tended to downplay the importance of surface interactions, aiming their efforts on reactions occurring in deeper waters. Our results reveal that the energy required for CO2 to react at the surface is comparable to that needed for reactions occurring much deeper in the water column. Both processes require about the same amount of energy.
Implications for Ocean Chemistry
With CO2’s increasing presence in the atmosphere leading to rising levels in Earth’s oceans, understanding its reaction with water is critical. This process is a main driver of ocean acidification, which threatens marine habitats and species. Brookes expressed concern regarding existing predictions:
“Unfortunately, this suggests that current predictions about changes in ocean pH, which measures its acidity, may be underestimated.” – Samuel Brookes
This grave underestimation can have ripple effects on marine biodiversity and the health of marine environments as a whole. The study underscores the immediate need to reconsider CO2 dynamics in aquatic systems. This is especially important as greenhouse gas emissions are rapidly changing ocean chemistry.
Future Research Directions
Schran and his team are hoping to take their research further. They are currently working to add more species such as sodium, chloride, and carbonate ions. These ions are ubiquitous in ocean waters and can affect the way CO2 reacts with water in solution. Schran noted:
“By moving CO₂ just a fraction of a nanometer—going from being on top of the water to residing in the topmost layer—we practically cut the barrier to reaction in half.” – Dr. Christoph Schran
Though new, this innovative approach provides fertile ground for future investigations. Now, researchers have an opportunity to investigate additional fundamental processes and reaction mechanisms that may be affected by such dynamics. The researchers are excited to see what other reactions can teach us about environmental change.