The ozone layer is recovering – a success that began 40 years ago with the Vienna Convention. Global measurements of ozone-depleting substances are also a key decision to success.   

March 22 marks the 40th anniversary of the Vienna Convention for the Protection of the Ozone Layer. This international agreement laid the foundation for the global protection of the stratospheric ozone layer in 1985 – and formed the basis for the later Montreal Protocol, which regulates the phase-out of ozone-depleting substances such as chlorofluorocarbons (CFCs). Thanks to continued scientific monitoring and policy action, the ozone layer has now recovered.

Jungfraujoch – lighthouse of the world’s measuring stations

Empa researchers have been measuring ozone-depleting substances and greenhouse gases on the Jungfraujoch for 25 years. However, a global measurement program was established in 1978 even before the ozone hole was discovered. Today, the high-alpine research station on the Jungfraujoch is part of the international “Advanced Global Atmospheric Gases Experiment” (AGAGE) network, which includes more than ten stations worldwide. “In total, we measure around 50 different trace gases – from ozone-depleting substances to pure greenhouse gases. Continuous measurements are a key decision in order to understand the evolution of these substances in the atmosphere and to estimate the amounts released by human activities,” says Empa atmospheric scientist Stefan Reimann.

On the Jungfraujoch, Empa researchers are interested in two types of air masses: on the one hand, clean air that is hardly influenced by European emissions, such as from the Atlantic Ocean. It serves as a reference for background pollution in the Northern Hemisphere and reveals global trends in halogenated hydrocarbons. On the other hand, the high-alpine measuring station also reaches regionally polluted air, revealing emissions from individual regions or countries. According to Empa researcher Martin Vollmer, a typical example of this are strong southerly winds, known in Switzerland as Foehn. “In such weather conditions, air from the heavily industrialized and densely populated Po plain in northern Italy reaches the Jungfraujoch. These air masses often contain many pollutants, which we analyze in detail here to better understand their sources and distribution.”

Key role in the discovery of new ozone-depleting substances

In addition to monitoring known substances, the Jungfraujoch plays a key role in the discovery of new ozone-depleting substances and other halogenated compounds that affect the climate. For example, the high-alpine monitoring station measured halogenated anesthetics and many new hydrofluorocarbons (HFCs), which are now regulated in an extension to the Montreal Protocol. Empa researchers also detected new substitutes for the banned CFCs, known as hydrofluoroolefins (HFOs). In addition, they achieved the world’s first evidence of substances that enter the atmosphere solely as by-products of industrial manufacturing processes. “Since some of these substances also deplete the ozone layer, our measurements help uncover potential gaps in the Montreal Protocol and ensure its long-term effectiveness,” explains Reimann.

Continuous monitoring is essential for the discovery of new substances. As soon as Empa researchers classify a new compound as relevant, it is included in the AGAGE network as well as in other measurement programs. “In the case of new substances, pollution is often rare in the beginning. It is only when they enter the atmosphere on a regular basis that larger emissions and their sources can be identified,” says Alina Begley, a postdoctoral researcher at Empa who investigates new ozone-depleting substances. “When the hydrofluoroolefin HFO-1234yf was first detected here in 2011, for example, the concentration was still very low. Today, it is the most widely used refrigerant component in car air conditioning systems worldwide.”

Calibration for the global measurement network

At the heart of the research station on the Jungfraujoch is the “Medusa” measuring system – a gas chromatograph mass spectrometer specially developed for the AGAGE network, which automatically measures numerous trace gases in the atmosphere. Standardized calibration procedures are essential to accurately determine even the smallest concentrations of ozone-depleting substances. Empa researcher Vollmer uses clean reference air provided by the “Scripps Institution of Oceanography” in California. “This allows us to calibrate all measuring instruments in the network to accurately measure even extremely low concentrations – down to a billionth of the CO2 concentration.”