The ozone layer, the fragile gas shield that surrounds the Earth and protects it from the harmful effects of ultraviolet radiation, faces a new threat. Although at the beginning of the year the United Nations announced that the ozone layer is recovering (at a rate of 1 to 3% per decade since the year 2000) thanks to the ban on chlorofluorocarbons (CFCs), a new A study by the Massachusetts Institute of Technology (MIT) has identified another threat that will slow down its recovery. It is chloroform, a colorless compound that is used in the manufacture of products such as Teflon and various refrigerants. The researchers found that between 2010 and 2015, chloroform concentrations in the global atmosphere had increased significantly.
Tracing the origin of these emissions, they observed that the production of chloroform products is increasing in East Asia. If there is no brake, the researchers predict that the restoration of the ozone layer could be delayed between four and eight years.
"The recovery is not as fast as people expected, and – in this study published yesterday in" Nature Geoscience "- we show that chloroform will slow it down even more," says Ronald Prinn, professor of Atmospheric Sciences at MIT and co-author of the study. together with Xuekun Fang.
Chloroform is a substance of so-called very short duration; that is, it decomposes after about five months, just like dichloromethane. If it does not put a brake on its production, it is more likely that this substance reaches the stratosphere, where, like CFCs, it decomposes into chlorine, which destroys ozone. The advantage of being a short-lived chemical component is that, if its emissions are cut, the benefits can be noticed in a short time. The problem: given that it is assumed that these very short-term substances are unlikely to cause real damage to ozone, the Montreal Protocol does not stipulate its regulation. "Now that the emissions of the longer-lasting compounds are decreasing, the additional recovery of the ozone layer can be stopped with relatively small sources, such as those of very short duration, and there are many," says Prinn.
To analyze the situation of the problem, the researchers monitored these compounds together with other gases with the Global Atmospheric Gas Experiment (Agage), a network of stations installed in coastal and mountainous areas around the world that measures the composition of gases in the atmosphere. since 1978. Each of these stations, 13 in total spread across America, Europe, Asia and Australia, records air intakes and allows researchers to analyze atmospheric concentrations of more than 50 greenhouse gases.
When Fang began to examine the data he noticed an increasing trend in chloroform concentrations around the world between 2010 and 2015. He also observed a chloroform accumulation three times higher in the northern hemisphere than in the southern hemisphere. Using an atmospheric model, the researchers estimated that, between 2000 and 2010, global emissions of chloroform remained at about 270 kilotons per year. However, after 2010, this figure increased, reaching a maximum of 324 kilotons in 2015. While most stations in the Agage network did not measure substantial increases in the magnitude of the chloroform peaks in Europe, Australia and western EE UU, in Hateruma (Japan) and another in Gosan (South Korea) showed dramatic increases in frequency and magnitude of the peaks in this gas.
"We came to the conclusion that East China can explain almost all of the global increase," says Fang. "We also discovered that the main chloroform production factories and the industrialized areas in China are spatially correlated with the critical emission points. And some industrial reports show that the use of chloroform has increased, although we are not completely clear about the relationship between the production and use of chloroform and the increase in chloroform emissions. "
"Ozone begins to recover and this is already significant in the high Antarctic stratosphere. In fact, the Antarctic hole starts later. The evaluation of the trends shows, however, that this recovery is about five years behind the estimates in the previous report ("Ozonoe Assessment 2014"). In general terms, this recovery is, in equal parts, due to the elimination of substances that destroyed the ozone layer (ODS) and the effect of climate change, since global warming favors the recovery of the ozone layer. This recovery is not uniform and is only observed in certain regions. There is no evidence that total ozone recovers, since the concentrations of the ODS are still very high. Although the treaty of Montreal and Kigali has been successful in eliminating emissions of these substances, the truth is that it has only disappeared from the atmosphere between 15 and 25%, "explains Alberto Redondas, ozone researcher at Aemet.
«This year – he continues – the ozone hole reached 25 million km2, like all of North America». In the year 2000, however, the hole over Antarctica was almost 60 times the size of Spain (29.9 million km2). There is still an important way to go to make the hole in the ozone layer history.