The success story of the Montreal Protocol

Ozone is vital for sustaining life. It is the only gas in the atmosphere capable of absorbing the dangerous ultraviolet radiation emitted by the Sun. It is unlikely that life would have ever evolved from the deep oceans to the Earth's surface 500 million years ago if we did not have a stable ozone layer. Ozone is thus not merely an air pollutant even though it is known as such in the lower atmosphere. By contrast, the ozone layer in the middle atmosphere is highly significant. However, a massive hole was detected in the ozone layer in 1985.

According to Erkki Kyrölä, a Research Professor at the Finnish Meteorological Institute, the observation was "natural sciences at their best", as the ozone hole was detected as the result of long-term measuring and monitoring work. "The information was obtained with routine work", Kyrölä explains. No one could have predicted the situation, which made ozone depletion evolve into an international shock.

"None of the theories at the time could explain the cause of the ozone hole", Kyrölä describes. "Atmospheric research was in turmoil and politicians were granting funding for ozone research. There was genuine fear of the spreading of the ozone hole over other continents as well. Both in science and in politics, it was quickly recognised that something needs to be done about this issue."

Ozone measurements from space

The Finnish Meteorological Institute began conducting ozone measurements in Sodankylä as early as in 1988. Ozone sounding was also carried out at the Jokioinen observatories and the Marambio Antarctic base in cooperation with Argentina. The political decision as a result of which Finland joined the European Space Agency (ESA) in the late 1980s was a further major financial investment in ozone research in Finland.

ESA (European Space Agency) was established to coordinate the satellite projects and research ideas of European countries. "It is the saviour of small countries such as Finland", Kyrölä notes. The United States has been the only country capable of conducing exhaustive measurements from space on its own.

In addition to ESA, NASA and many other space institutions began planning new satellite instruments, in other words measurement equipment to be set up in space for the purpose of ozone monitoring. In 1988, Finland was involved in designing and utilising the French GOMOS instrument. For 10 years, GOMOS travelled on a polar orbit at the altitude of 800 kilometres on board the ENVISAT, a satellite platform the size of a bus, until the end of its mission in April 2012. GOMOS enabled recording a lot of important data about ozone.

In the summer of 2004, the OMI instrument by a Finnish-Dutch team was launched on its orbit on board a US satellite. Finns were also involved in the Odin minisatellite mission led by Sweden. The Finnish Meteorological Institute processes the minisatellite's ozone products. The Finnish Meteorological Institute is also in charge of the processing of the ultraviolet radiation measurements by OMI.

Propellants are the most effective ozone depletors

It did not take long to discover the causes of the ozone hole in the 1980s. Propellants, i.e. CFCs, were the worst ozone depletors. Once CFCs make their way into the middle atmosphere, the ultraviolet radiation is strong enough to release the chlorine in the compound into the air. Chlorine and ozone react with each other catalytically, as a result of which the amount of chlorine remains unchanged in the reaction, but ozone is destroyed. The increase in the amount of chlorine explains the general ozone depletion but not the magnitude of the ozone hole. An explanation can be found in the reservoir compounds which bind some of the chlorine and other catalysts.

During winter, a polar vortex is formed over the Antarctic, and the cold air is not mixed with the air of other latitudes. As a result of this phenomenon, polar stratospheric clouds form at the altitude of around 20 kilometres. The different reservoir compounds react on the cloud surface and the chlorine absorbed in the atmosphere is released in a molecular form. Once the sun begins to shine on Antarctica in late September to early October, the potent UV radiation splits the molecular chlorine into chlorine atoms, which begin to destroy ozone catalytically. In this changed state, chlorine is extremely harmful for ozone. As temperatures are not as low elsewhere in the atmosphere, intense ozone depletion has not occurred elsewhere in the world.

Recipe for a disaster

If the response to the Antarctic ozone hole had not been quick and efficient enough, the consequences would have been catastrophic. It is estimated that the general ozone depletion would have been 17 per cent in 2020. After 2050, the rate would have climbed to 67 per cent. This would have resulted in year-round ozone holes over both polar regions, double the amount of ultraviolet radiation on Earth and considerably higher incidence of skin cancer.

However, these fateful scenarios did not materialise outside of artificial atmosphere simulations, and for this we owe thanks to the Montreal Protocol. The Protocol was ratified in every countries in the world on 16 September 1987, after which the manufacture and sales of ozone-depleting substances was heavily restricted. The ozone layer is now expected to fully recover back to its previous concentrations.

Long-term research and post-monitoring

The Montreal Protocol has been extended and specified, and its implementation has been regularly monitored up to this day. CFC concentrations and ozone recovery continue to be measured. According to Kyrölä, constant observation of the situation and long time series in the observations are vital for problem-solving related to ozone depletion.

30 years ago, long-term monitoring revealed the existence of the ozone hole and enabled averting a global environmental disaster. "It must have been extremely tedious work, until it wasn't", Kyrölä reminisces. "All of a sudden, the entire field of atmospheric research was electrified." According to Kyrölä, the intensified measurements must be continued for at least another 30 years.

Ozone layer recovery continues to be actively monitored in international cooperation between different research institutes. The Montreal Protocol succeeded in stopping ozone depletion as it resulted in ceasing the production and sales of ozone-depleting substances worldwide.

No more ozone-depleting substances are released into the atmosphere, but the elimination of the remaining substances will take its time. When no more ozone-depleting substances are streaming upwards into the middle atmosphere, the substances resume their natural concentrations. Although recovery is a slow process, we have plenty of reason to celebrate the 30th anniversary of the Montreal Protocol.