Insights into the roles of aerosol particle surfaces
Airborne particles are all around us and impact on us in a variety of ways, from vectors for viruses to drivers of climate change. The relationship between the particles we emit and the environment which surrounds us is complex, and the need to improve our understanding of the dynamic is urgent. The SURFACE project, with support from the European Research Council(opens in new window), aimed to do just that. “Every single cloud droplet has been nucleated on the surface of an aerosol particle. Aerosols and droplets provide the media for condensed-phase chemistry in the atmosphere, but large gaps remain in our understanding of their formation, transformations and climate interactions,” says principal investigator Nønne Prisle(opens in new window), professor at the Center for Atmospheric Research(opens in new window).
Chemical reactions and physical transformations in the atmosphere
The atmosphere comprises a vast number of different chemical species, each of which is present in very small amounts. These can take part in a myriad of different chemical reactions and physical transformations. “The reactions and transformations all happen at the same time, but on very different timescales, so they are virtually impossible to untangle, through either experiments or theory,” explains Prisle. When it comes to aerosols, analysis is equally challenging. They range dramatically in size, contain many different molecules condensed together, and are still so small that the total amount of material is very sparse. As Prisle notes: “Instruments have been developed to detect the composition of surfaces. But only very recently has it become possible to use them for surfaces of material relevant for the atmosphere. These experiments are very difficult to carry out and to analyse, so our experiments are some of the first to achieve this.” One of the key methods SURFACE used is synchrotron-based photoelectron spectroscopy(opens in new window). This harnesses powerful X-rays, generated at large synchrotron facilities, to investigate samples on the molecular level. “The X-rays kick out electrons from the molecules in the sample, and we collect these electrons and measure their speed. From this speed, we can determine the identity of the molecules in the surface and their surroundings. From the number of electrons we detect, we can determine the amount of each specific type of molecule,” Prisle explains. The project then went on to generate aerosol samples in atmospheric simulation chambers. “We used a range of instruments, some of them globally unique, to investigate their physical and chemical properties, and their ability to form cloud droplets and affect atmospheric chemistry.” After investigating the physical properties of the samples, SURFACE developed computationally efficient ways to include these in climate models. “The models revealed that surface properties can influence aerosol effects on a global scale,” remarks Prisle.
Impact of surface-specific properties on aerosol effects
SURFACE, conducted at the University of Oulu(opens in new window) in Finland, has demonstrated the clear and significant impact of surface-specific properties on aerosol effects, at every level. “I think you could call these effects fingerprints,” she says. “Our research has really opened a whole new dimension that should be taken into account, such as the chemical composition and physical conditions, when we interpret and predict effects of aerosols in the atmosphere,” adds Prisle.
