Ozone layer
Ozone in the atmosphere is most abundant in the stratosphere, between 15 and 50 km altitude. The ozone layer protects Life on Earth on land and in the oceans by absorbing biologically harmful ultraviolet radiation from the Sun. In the mid-1970, it was discovered that some gases released by human activities destroy ozone in the stratosphere. This destruction can be severe as in Antarctica during springtime (the ozone hole). Since, ozone depleting gases are forbidden or regulated by the Montreal protocol and monitoring of ozone has been intensified, using ground-based and satellite instruments.
FAQ on Stratospheric Ozone: in this page, you will find all you want to know about ozone layer and its depletion!
How GEOmon improves knowledge on stratospheric ozone?
GEOmon delivers improved long-term time series of stratospheric ozone and related species from various ground-based stations and provides modelling tools.
GEOmon monitors key variables relevant to the issue of stratospheric ozone depletion at various European stations contributing to the NDACC (Network for the Detection of Atmospheric Composition Changes) and to improve understanding of its link with climate change. The variables targeted by GEOmon for observation are ozone, chlorine, bromine, fluorine and nitrogen species, stratospheric water vapour, temperature, polar stratospheric clouds (PSCs) and stratospheric aerosols.
The measurements obtained within GEOmon are compared with satellite observations and the long-term evolution of the various species are analysed.
Evolution of ozone anomaly at an altitude around 40 km at a NDACC station
This figure shows ozone anomaly over the 1979-2008 period from different data sets produced at the station of Hohenpeissenberg. Ozone anomaly is computed from the deviation of monthly ozone mean value for a particular month (e.g. June 2000) from the average ozone value obtained during the same month over the whole period (climatological mean). Anomaly is computed at around 40 km (ozone profile measurement is on average from 35 km to 45 km). This graph allows the comparison of measurements from ground-based instruments (lidar and microwave spectrometers) and from three satellites. The range of several model simulations can also be visualised.
All measurements show an increase in the anomaly up to 1996-1997 with a stabilisation thereafter.
Evolution of ozone anomalies at an altitude around 40 km at five NDACC stations
Other GEOmon measurements (on a page Science)
Example of evolution of an ozone destructor in the atmosphere: inorganic chlorine
The release of chlorinated compounds in the atmosphere since the 70s has caused destruction of stratospheric ozone at the global scale. Thanks to the measures taken in the Montreal Protocol (1987) and its Adjustments and Amendments, the release of chlorinated compounds has decreased dramatically. Consequently, the amount of inorganic chlorine in the atmosphere has reached its maximum around 1997 and since then has started to decline. HCl is the major reservoir of inorganic chlorine in the atmosphere. So observations of HCl are representative of the total atmospheric inorganic chlorine amount.
This figure shows an example of remote sensing observations of the total column abundance of HCl in the atmosphere above Kiruna (Sweden), made with a high-resolution Fourier transform infrared solar absorption spectrometer. The observational data are confronted with simulations of the time evolution of HCl computed with two global 3D (the 3 dimensions are latitude, longitude, altitude) chemistry-transport models (KASIMA, SLIMCAT), and a 2D model. We can see that the amount of HCl in the atmosphere has reached its maximum around 1997 and then has started to decline slowly.
Such observations are made worldwide. In the frame of GEOmon, the observations at 16 stations have been compared with corresponding model simulations to detect the growth and decline rate of HCl in the atmosphere on the global scale and to study the relationship with the regulations of the Montreal Protocol and the impact on the evolution of stratospheric ozone.
International Policy on Climate and the Environment
The Montreal Protocol on Substances That Deplete the Ozone LayerIn 1985 the Vienna Convention established mechanisms for international cooperation on research into the ozone layer and the effects of ozone-depleting substances (ODS). In response to growing concerns about the ozone layer linked to the discovery of the ozone hole over Antarctica, the Montreal Protocol on Substances that Deplete the Ozone Layer was signed in 1987 and, following ratification, entered into force in 1989. The Protocol established legally binding controls for developed and developing nations on the production and consumption of halogen source gases known to cause ozone depletion. At meetings in London (1990), Copenhagen (1992), Vienna (1995), Montreal (1997), Beijing (1999) and Montreal (2007) amendments were adopted in order to speed up the phase-out of ODS.
In addition, the Protocol obliges all parties to ban trade in ODS with non-parties. It promotes technical assistance to developing countries for the production of substitutes and requires an assessment of the control measures every four years on the basis of available scientific, environmental, technical and economic information.
A multilateral fund was established to help developing countries meet the costs of the ODS phase-out. Go to the UNEP web site to learn more about the Montreal Protocol.
