In addition to greenhouse gases, the atmosphere contains other substances that influence the climate. One of these is ozone. Although ozone acts as a greenhouse gas, it also protects us from harmful ultraviolet radiation. Particulate matter and other minute particles are also found in the atmosphere. They have a predominantly cooling effect on the climate because they reflect incoming solar radiation back into space.
Humans impact the climate in various ways, and not only through carbon dioxide emissions. In addition to other greenhouse gases that persist for a long time in the atmosphere, such as methane and nitrous oxide (laughing gas), numerous climate-influencing substances are emitted as a result of industrial and domestic activities, and transportation. Humans thus alter the composition of the atmosphere which, as well as having a detrimental effect on air quality, also affects the climate. One of these substances is ozone. At altitudes close to the ground, ozone is a relatively short-lived greenhouse gas. At higher altitudes, it serves as a shield against dangerous ultraviolet radiation. In Switzerland, measurements of the ozone column have been taken continually since 1926.
Moreover, human activities emit particulate matter and other minute particles known as aerosols. The many and varied effects of these particles on the climate are currently not fully understood, and therefore contribute substantially to the uncertainties in climate projections. The long-series particle measurements taken on the Jungfraujoch over many years help us to gain a better understanding of the effects of aerosols on the climate.
Ozone is an irritant gas that can have a detrimental effect on health. As a greenhouse gas, it is also contributing to global warming. Due to its reactivity, however, it is shorter-lived than other greenhouse gases. At the same time, ozone is indispensable for life on Earth, as the ozone layer at an altitude of 10-40 km actually protects us from harmful solar UV radiation.
In the last century, emissions of hydrochlorofluorocarbons (HCFCs) used, for example, as propellants in spray cans, led to a concerning degradation of the ozone layer. HCFCs were banned with the entry into force of the Montreal Protocol in 1989, which resulted in the stabilisation of the ozone layer at low ozone concentrations.
Measuring ozone levels is an important task of MeteoSwiss. Long-term data series are fundamental to being able to recognise changes over longer time periods. Ozone measurements began in Switzerland back in 1926 in Arosa, moving to Davos in 2021, where they are now continuing. The Swiss ozone data series is the longest in the world, and is therefore extremely valuable when it comes to analysing long-term changes in the ozone layer. Between 1930 and 1970, the average annual ozone reading in Arosa fluctuated around 330 DU (Dobson units); 100 DU is equivalent to 1 mm of pure ozone at the normal pressure of 1,013 hPa and 0°C. Between 1970 and 1990, the value reduced to around 310 DU due to the use of ozone-depleting substances. Since then, ozone levels have stabilised, within the bounds of normal annual fluctuations.
Aerosols are liquid or solid particles with a size of between one nanometre and ten micrometres. They come in a wide variety of forms and can be of natural origin or produced as a result of human activities. Examples of natural aerosols include sea salt, pollen, mineral dust and bacteria. Anthropogenic aerosols are, for example, soot particles, or ammonium sulphate used as a fertiliser.
Aerosols have an impact on the radiation balance of the Earth’s surface. Overall, they have a cooling effect on global temperature because they reflect a proportion of solar radiation back into space. Aerosols are also indispensable for cloud formation. In order for cloud droplets to form, water vapour in the atmosphere must be able to condense on a surface. In this process, aerosols function as so-called condensation nuclei. If there are higher amounts of aerosols in the atmosphere, this leads to thicker cloud, which in turn can contribute to cooling or warming of the atmosphere, depending on the height and the type of the cloud. The complex effects of aerosols are difficult to quantify even today, and contribute significantly to the uncertainties in climate simulations.
MeteoSwiss measures aerosol variables at numerous locations. In addition to the aerosol concentration in the air, the optical and other properties of aerosols are also measured. These measurements allow meteorologists to draw conclusions about the aerosol types present, and their effects on climate. The measurements recorded on the Jungfraujoch (3,580 m a.s.l.) are of particular significance, as the fluctuations in concentration levels are less severe at this altitude, which affords a clearer picture of long-term changes.