Scientists provide new insights into how air pollution forms at the molecular level

A team of researchers has made a discovery in understanding how air pollution is formed at the molecular level. Their research, published in the journal Nature Communications, sheds light on the complex chemical processes that occur at the interface between atmospheric liquids, particularly aqueous solutions and vapors.

This international study focuses, on the one hand, on the differences in the complex acid-base equilibrium (i.e. the ratio of basic to acidic components) inside the solution, and on the other hand, on the interface itself between the solution and the surrounding vapor. I’m guessing. Although it is easy to measure acid-base equilibria throughout a solution using state-of-the-art methods, it is difficult to determine these equilibria at the interface between the solution and the surrounding gas phase.

Although this boundary layer is about 100,000 times narrower than a human hair, it plays a crucial role in processes that affect air pollution and climate change. Therefore, investigating the chemistry of the solution-vapor interface at the molecular scale will help develop improved models to understand the fate of aerosols in the atmosphere and their impact on Earth’s climate.

Key findings include:

Determining complex acid-base equilibria: Researchers used complementary spectroscopy to unravel the complex acid-base equilibria that occur when the pollutant sulfur dioxide (SO2) is dissolved in water. Unique behavior at the liquid-vapor interface: Under acidic conditions, the tautomeric equilibrium between bisulfite and sulfonate is strongly shifted towards the sulfonate species. Stabilization at the interface: Molecular dynamics simulations revealed that the sulfonate ion and its acid (sulfonic acid) are stabilized at the interface by ion pairing and a higher dehydration barrier, respectively. This explains why the tautomeric equilibrium shifts at the interface.

This finding highlights the contrasting behavior of chemicals at interfaces and in the bulk environment. This difference greatly affects how sulfur dioxide is absorbed and reacts with other pollutants in the atmosphere, such as nitrogen oxides (NOx) and hydrogen peroxide (H2O2). Understanding these processes is critical to developing strategies to reduce air pollution and its negative effects on health and the environment.

The team includes the Fritz Haber Institute of the Max Planck Society in Berlin, the Qatar Institute for Environment and Energy Research/Hamad Bin Khalifa University, the synchrotron PETRA III in Hamburg and SOLEIL in Zif-sur-Yvette (France), the Sorbonne Includes university research. University of Paris, ETH Zurich, PSI Center for Energy and Environmental Sciences (Switzerland)