In the early 1970s, ozone measurements in the stratosphere revealed first signs of human-induced climate change. This triggered a rethinking and the initiation of a variety of measures aimed at protecting the ozone layer on a global level (Montreal Protocol). Continuous monitoring of the ozone layer is vital to review the effect of the implemented procedures.
The stratospheric ozone layer is situated at an altitude between 10 and 30 km. The high ozone concentration is capable of almost completely absorbing the harmful shortwave UV radiation of the sun and is therefore vital for the protection of any forms of life on Earth. For example, excessive skin exposure to UV radiation can cause skin cancer in humans. In contrast, high ozone concentrations at ground level are harmful for humans and nature, because the gas is extremely reactive. This can cause respiratory problems in humans or impaired growth in plants.
The problem of ozone layer depletion has yet to be resolved
International conventions such as the Montreal Protocol, which was enacted in the late 1980s, ban the use of substances that are harmful to the ozone layer. But even though these agreements are slowly having an effect, the ozone layer continues to be at risk:
- The ozone layer has not been completely restored; it does not correspond to the state it had achieved prior to 1970, and it is expected to take several decades before this goal is reached.
- The ozone layer depletion at the South Pole (Antarctica) is a recurring yearly phenomenon.
- Ozone depletion was observed at the North Pole (Arctic) for the first time in 2011.
- Climate change and the alteration of the ozone layer are closely related.
Measuring and analysing the ozone development in the different layers of the atmosphere are therefore essential.
Ozone measurements are a Swiss tradition
Switzerland has a long history of conducting ozone measurements in the upper atmosphere. As early as 1926, Prof. P. Götz started measuring the ozone levels in Arosa, and these measurements have continued with almost no interruptions ever since. This worldwide unique series of measurements makes it possible to study the development of the ozone layer over a very long period of time. The data was acquired by means of different Dobson and Brewer spectrophotometers.
The very long series of measurements demonstrates the thinning of the ozone layer that occurred between 1970 and 1995. The decline starts at around 1970, because the emissions of ozone-depleting substances (CFCs) rose sharply during this period. Since the mid-1990s, the ozone layer has restabilised on a lower level.
Ozone profile measurements
The weather service MeteoSwiss is using different techniques to measure the ozone profile, which cover a variety of spatial and chronological levels.
|Type of measurement||Frequency||Scope||Resolution||Chronological level|
|Reversal method (Dobson, Brewer)||2 profiles/day
(provided the sun is visible)
|10 – 50 km||5 - 7 km||since 1957|
|Ozone probe||3 profiles/week||0 - 35 km||0,15 km||since 1966|
|Microwave radiometer||3 profiles/week||25 - 70 km||7 - 15 km||since 2000|
Caption: Overview of methods used to measure the ozone profile
Ozone measurement using balloon probes
Ozone measurements using balloon probes have been introduced in Switzerland in 1966 by Prof. H. U. Dütsch of the ETH [Federal Institute of Technology] Zurich. They have been conducted in Payerne since 1968. This uninterrupted series of probes helps us track the development of the ozone quantity in the different atmospheric layers.
Statistical analysis of the series of ozone measurements
The series of measurements with different lengths from the weather service MeteoSwiss can be used to calculate the change in ozone concentrations during a ten-year period. The images show the results of the analysis from the different ozone probes at the corresponding altitudes. The result of the analytical measurement for the period from 1970 to 1995 is shown on the left and for the period from 1995 to 2012 on the right.
Above an altitude of about 12 km (stratosphere), the ozone concentrations have decreased during the first period and stabilized over the course of the second period. Below an altitude of 10 km (troposphere), the trend is reversed.
The black dots indicate the average changes in concentration. The grey zone represents the statistical 95% confidence interval. All trend values are statistically relevant in the period from 1970-1995 (on the left), because the grey zone never crosses the zero axis. In contrast, the trend values between 1996 and 2009 are statistically not significant, because the grey zone usually coincides with the zero axis. The dotted bold red vertical line corresponds to the decrease of the entire ozone column in percent. Between 1970 and 1995, it has decreased by nearly 2 percent every ten years. No change is observed between 1996 and 2009. The thin red lines reflect the 95% confidence interval.
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