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 Uz halogenirane ugljikovodike, sumporni dioksid iz industrijskih ispusta i vulkanskih erupcija također doprinosi razgradnji ozonskog omotača. Osim što predstavlja ozbiljan okolišni problem, prisutnost sumpornog dioksida u našoj atmosferi pridonosi ljepoti zalazaka sunca povećavajući udio čestica na kojima se svijetlost lomi i rasipa.

The ozone hole over the Antarctic is closing up

As long ago as 1985, the journal Nature published a paper describing extensive damage to the ozone layer above the Antarctic. The study brought together data collected by British scientists during their wide-ranging research of the Earth’s stratosphere over the southern hemisphere. That was the first time the depleting ozone layer over the Antarctic was referred to as the ozone hole.

In fact, the beginning of the story of the ozone hole can be traced to the start of the last century and the industrial-scale production of gaseous halogenated carbohydrates, commercially known as Freon and Halon. Wide application in refrigerating devices, solvents, pesticides, fire suppression compounds, glues and plasticizers, as well as in a number of other industrial processes, all led to the mass production of freons and halons. For several decades large quantities of halogenated carbohydrates were released into the environment, without being considered harmful. Then in 1974 the laboratory tests of Mario Molina and Sherwood Rowland led to the theory that freons and halons could accumulate in the upper layers of the atmosphere and cause the breakdown of ozone molecules. Over the next few years, extensive field research confirmed the harmful effect of freons and halons on the ozone layer, ultimately leading to the signing of the Montreal Protocol in which signatory countries agreed to reduce the use of freons by 50%. Further revisions to the Protocol enforced a full ban on the use of most halogenated carbohydrates. Up to date 197 countries have signed the Montreal Protocol.

Despite reduced emissions of halogenated carbohydrates, in the decades that followed, the results of measuring the area of the Antarctic ozone hole gave little cause for optimism. The data clearly pointed to an upward trend in the expansion of the ozone hole, from a mere 0.1 million km² in 1979 to as much as 25.6 million km² by 2015. The trend was explained by the slow migration of halogenated carbohydrates in the upper layers of the atmosphere and by the fact that they remain active for several decades upon their release. Data published in the June 2016 edition of Science, however, suggest a new denouement to the ozone-hole story. Namely, it is known that the breakdown of ozone by halogenated carbohydrates requires sunlight. In the Antarctic, conditions for this arise in late August at the end of the polar night. Under the influence of the sun’s rays, ozone molecules begin to break down and the ozone hole rapidly forms, reaching its maximal size by early October. To have a clear picture of the effect of halogenated carbohydrates on the speed of ozone-hole creation, scientists sought to analyse data on the quantities of all hazardous compounds above the Antarctic in the first half of September, when the hole begins to form and when there are considerably fewer variations in the chemical reactions in which halogenated carbohydrates take part.  Research was conducted in the period 2000 – 2015 with the help of meteorological balloons and satellites. In additions to quantities of halogenated carbohydrates, other parameters responsible for ozone-hole formation were also monitored, such as temperature, wind and the amount of sulphur dioxide generated by volcanic eruptions. Data analyses confirmed that the overall area of the ozone hole over the Antarctic had shrunk by more than four million km² in the period 2000 – 2015! Misleading among the data was the size of the ozone hole measured in 2015, which was almost the same as the record size of 2000. Additional data analysis showed that the 2015 size of the hole was caused by the eruption of the volcano Calbuco in Chile in April of the same year, which discharged huge amounts of fine particles into the atmosphere. This discharge increased the total amount of stratospheric clouds above the Antarctic, thus facilitating the expansion of the ozone hole. Regardless of occasional volcanic eruptions, computer models based on the data from the studies mentioned predict that all atmospheric halogenated carbohydrates will have fully broken down by the middle of the twenty-first century, allowing the Antarctic ozone hole to completely close.

In light of these latest discoveries, the Montreal Protocol serves as a shining example of how global environment issues can be resolved. By taking scientific facts into consideration and making joint decisions, sometimes at the expense of economic growth, it could be possible to close many other open environmental problems, just like the ozone hole over the Antarctic.

Text and photographs by Patrik Krstinić, biology teacher

Photo 2. Industrially produced gaseous halogenated carbohydrates are broken up high in the atmosphere by the sun’s rays. The free radicals released (fluorine, bromine, chlorine) latch on to ozone molecules, causing their breakdown. One halogenic radical is capable of destroying 100,000 ozone molecules before it descends into the lower layers of the atmosphere. Because of the depleted ozone layer, more harmful UV-B rays reach Earth and cause damage to the cells of living organisms.