The combined emissions of five types of chlorofluorocarbons (CFCs), manmade gases that destroy the ozone layer situated in the Earth’s upper atmosphere, increased 2.6-fold during the past decade. In 2020, the concentration of this group of CFCs was the highest ever recorded. The ozone layer protects inhabitants of the planet from the harmful action of ultraviolet rays from the Sun, which can cause skin cancer, immune problems, and other disorders. The data are part of a study published in April in the journal Nature Geosciences and they surprised its authors.
Chlorofluorocarbon emissions should not have increased in the past decade. Since 2010, in accordance with the Montreal Protocol, an international treaty that controls the production of gases that deplete the ozone layer, the manufacture of CFCs for any purpose has been prohibited across the globe. There is only one exception to this rule: the gases can be produced as a raw material for the generation of other chemical products. In this case, it is expected that all or almost all the CFCs are consumed in the intermediate reactions that lead to the creation of other compounds, a scenario which, theoretically, would not lead to the release of chlorofluorocarbons into the atmosphere.
Created artificially, CFCs are carbon-based compounds that contain chlorine and fluorine. They do not freely exist in nature and were widely used until the beginning of this century in a range of products: in the refrigeration systems of refrigerators and air conditioning units, as propellants of aerosols, solvents, and in foam filling.
Three of the five compounds with increased emissions — CFC-113a, CFC-114a, and CFC-115 — may be unwanted byproducts from the manufacture of hydrofluorocarbons (HFCs), artificial gases that have substituted chlorofluorocarbons in many applications. HFCs do not destroy the ozone layer, but, like CFCs, they are greenhouse gases that contribute towards increasing the planet’s average temperature, the main cause of the climate crisis. It is not known what the origin is of the other two compositions with increased levels, CFC-112a and CFC-13.
Two studies published in the journal Nature, in 2018 and 2019, observed an increase in the past decade of another type of chlorofluorocarbon, CFC-11, and associated it to noncompliance of the protocol by industries in China. After these observations were published, emissions of CFC-11 fell again. “This increase was detected by scientists from different institutions, including NASA [North American Space Agency],” says Suely Machado Carvalho, senior expert from the technology and economic assessment panel of the Montreal Protocol, who represented Brazil in the negotiations that led to this agreement. “Since then, China has committed to improving the monitoring of emissions and local inspection.”
“Chlorofluorocarbons have a half-life in the atmosphere of over a century and their effects last for a long time,” comments British physicist Luke Western, from the University of Bristol in the UK and lead author of the article, in an interview with Pesquisa FAPESP. To carry out the study, the team of researchers used samples collected from 14 long-term gas measurement stations spread across the world. These recordings are part of the efforts made by the National Oceanic and Atmospheric Administration (NOAA), from the USA, and by the Advanced Global Atmospheric Gases Experiment (AGAGE), an international network that has been making this type of observation since the end of the 1970s.
Despite the upwards curve, the growing concentrations of the five CFCs, according to the study, should not cause further damage to the ozone layer, the most affected portion of which is located over Antarctica, in the southern hemisphere. Together, the emissions of these compounds during the past decade may cause a loss of just 0.002% of the ozone present in the entire stratosphere, the layer of the atmosphere found at between 10 and 50 kilometers of altitude, or 0.01% of the layer of this gas above Antarctica in the period between August and December. Since the adoption of the Montreal Protocol, signed in 1989, the ozone layer has been recovering and projections indicate that it should be fully recovered in the 2060s if there is no change to the current trend.
Chlorofluorocarbons cause chemical reactions when they reach Earth’s stratosphere. Their molecules breakdown upon being exposed to ultraviolet radiation. The chlorine atoms released by this breakdown disintegrate the ozone molecules they encounter. This makes the ozone layer thinner and its capacity to protect the Earth from ultraviolet radiation is reduced. The 1995 Nobel Prize in Chemistry was given to three researchers who, from the 1970s, studied the formation and deterioration of the ozone layer: Mario Molina (1943–2020) from Mexico, Paul J. Crutzen (1933–2021) from Holland, and Frank Sherwood Rowland (1927–2012) from the USA.
Increasing the size of the so-called hole in the ozone layer is not the only problem caused by CFCs, as highlighted by chemical engineer Damaris Kirsch Pinheiro, of the Federal University of Santa Maria (UFSM), coordinator of the Modeling and Forecasting Secondary Effects of the Antarctic Ozone Hole (MESO) project, a partnership between institutions from Brazil and France. “These gases are heavy contributors to the greenhouse effect,” says Pinheiro, who did not take part in the international study with the five types of CFCs (the study has no Brazilian coauthors). “Some of them end up being much more potent than carbon dioxide [CO2, the main greenhouse gas]. In other words, one CFC molecule, depending on which one it is, may cause the same greenhouse effect as 5,000 CO2 molecules,” she explains. In terms of the potential greenhouse effect, the accumulated effect of the emissions of all five of the analyzed CFCs is equivalent to one and a half times the carbon dioxide emitted in London in 2018.
For US biochemist Ray Weiss, of the Scripps Institute of Oceanography at the University of California, San Diego (UCSD), the new study also signals the importance of having means to measure different types of gases that can be found in the atmosphere. Sometimes, some of them are in greater quantities than expected or forecasted in scientific works.
Weiss, a coauthor of the article in Nature Geosciences, gives an example. “There is a compound called nitrogen trifluoride [NF3], used in the manufacture of televisions and computer screens. It was believed that 2% of the gas produced would go to the atmosphere until researchers took measurements and saw that 9% of the nitrogen trifluoride escaped from the factories,” says Weiss to Pesquisa FAPESP. “The discrepancy [between the estimate and reality] was from not knowing how this gas leaves the electronics production plants and ends up in the atmosphere.” Additionally, it is also suspected that a portion of the factories do not destroy the NF3 as they should, seen as this process is expensive. This gas is 17,000 times more potent than CO2 for causing the greenhouse effect over a period of 100 years.
“It would be extremely relevant to have more measurement stations for these types of greenhouse gases in the world,” says Pinheiro. There are no dedicated instruments for recording the concentration of CFCs and HFCs in Brazil, but, according to the researcher from UFSM, it would be important to have a station for such a purpose in the Southeast, which is home to the majority of the national industrial park. “We do not know if we have emissions of these gases because we do not take measurements,” adds Pinheiro. “Only when we have this type of data will we actually know how we are implementing the Montreal Protocol in the country.”
WESTERN, L. M. et al. Global increase of ozone-depleting chlorofluorocarbons from 2010 to 2020. Nature Geoscience. april 3, 2023.
RIGBY, M. et al. Increase in CFC-11 emissions from eastern China based on atmospheric observations. Nature. may 23, 2019.
MONTZKA, S. A. et al. An unexpected and persistent increase in global emissions of ozone-depleting CFC-11. Nature. may 17, 2018.