Atmosphere in X-ray light

Ozone in the upper atmosphere protects us from hazardous UV radiation. However, too much ozone in the air we breathe can endanger our health. Ideally and most frequently, the concentration of ozone in the lower layers of the atmosphere is safe and largely constant as long as summer smog is not prevalent. This is because the processes by which ozone is formed or decomposed keep things more or less in balance. To this end, bromine and related chemical elements such as chlorine and iodine in the air make an essential contribution to this balance. Globally, they are responsible for around 50% of all ozone decomposition.

Ozone, in turn, shares responsibility for the formation of bromine in the atmosphere. That's because bromine forms when bromide comes into contact with ozone from the air. This happens at the ocean's surface due the presence of bromide in seawater and also on the surface of small droplets (or particles) that arise from wave breaking and ocean spray. Since 70% of the Earth is covered with oceans, this happens globally on a massive scale. Recently, researchers at the Paul Scherrer Institute PSI have uncovered details of this important ozone-bromide chemical reaction. To do that, they recreated the processes at the water's surface and analysed them with the help of X-ray light from the Swiss Light Source SLS at PSI. Theoretical calculations carried out by researchers at institutions in Switzerland, the USA, and Qatar helped in interpreting the measurements.

Research options that are unique worldwide

SLS is a large-scale research facility that generates especially intense X-ray light customised to the exact requirements of different experiments. The centerpiece of the facility is a ring-like electron accelerator 288 metres in circumference. With the X-ray light from SLS, individual substances can be accurately detected even when they are in existence for only a very short time. We were able to show that a compound of bromide and ozone is created for a short time during the chemical reaction at the surface of the water, which had been predicted from theory but has been impossible to observe until now, says Luca Artiglia, the scientist responsible for the experiment. Markus Ammann, Head of the Surface Chemistry Research Group at PSI explains, These results not only help to understand the bromine chemistry in the atmosphere, but they also will be integrated into future atmospheric models to understand the development of the climate and air composition. At the same time, they show that the one of a kind experimental chamber constructed by the PSI researchers really does make anticipated chemical insight an observable reality. In the future, the chamber will be available to other researchers who study processes on surfaces in the context of energy and environmental research, Artiglia points out.

Text: Paul Scherrer Institute/Paul Piwnicki

About PSI

The Paul Scherrer Institute PSI develops, builds and operates large, complex research facilities and makes them available to the national and international research community. The institute's own key research priorities are in the fields of matter and materials, energy and environment and human health. PSI is committed to the training of future generations. Therefore about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether PSI employs 2100 people, thus being the largest research institute in Switzerland. The annual budget amounts to approximately CHF 380 million. PSI is part of the ETH Domain, with the other members being the two Swiss Federal Institutes of Technology, ETH Zurich and EPFL Lausanne, as well as Eawag (Swiss Federal Institute of Aquatic Science and Technology), Empa (Swiss Federal Laboratories for Materials Science and Technology) and WSL (Swiss Federal Institute for Forest, Snow and Landscape Research).

(Last updated in May 2017)