1982 to 2018, the ozone layer above Antarctic hole area (Image source: NASA Ozone Watch)
In the 1980s, humans first realized that our ozone layer was disappearing. As humans emit large quantities of HCFCs (chlorofluorocarbon, referred to as CFC) with the trade name " Freon " [Note 1] , the ozone level in the ozone layer once dropped at an astonishing rate. As the ozone layer disappears, high amounts of ultraviolet rays enter the atmosphere, which may induce skin cancer and cataracts and threaten the survival of marine plankton.
These freons discharged into the atmosphere are derived from refrigerant used in industrial production and foaming agent . In the 1980s, these chemical products containing Freon were widely present in common items such as refrigerators, fire extinguishers, foam polystyrene, etc. Among them, dichlorodifluoromethane (CFC-12 for short) and trichloromonofluoromethane (CFC-11), the former is a refrigerator refrigerant, while the latter is a commonly used foaming agent.
In view of the direct and close link between Freon emissions and the disappearance of the ozone layer, representatives of 26 countries gathered in Montreal, Canada in 1987 to sign the "Montreal Protocol" (hereinafter referred to as the "Protocol". The Protocol makes extremely strict provisions on the production of a variety of HCFC compounds, including CFC-11 and CFC-12, and requires countries to actively take preventive measures when they discover activities that have adverse effects on the ozone layer and stop related activities in a timely manner. At the same time, the Protocol also stipulates that the world should completely stop production of Freon by 2010.
Since the Protocol came into effect in 1989, 197 countries have signed and adopted the Protocol, and the ozone layer over Antarctica has finally entered a long recovery period. According to a forecast released by the United Nations Environment Agency and the World Meteorological Organization in 2014, if the level of freon in the atmosphere continues to decline steadily, the ozone layer will return to its state in 1980 between 2050 and 2070.
However, in 2018 and 2019, two studies published in Nature pointed out that the concentration of CFC-11 in the atmosphere showed an unexpected increase of , and this increase is likely from in eastern China, especially Shandong and Hebei. This undoubtedly casts a shadow on the recovery of the ozone layer.
Just before the Spring Festival, the latest research from Nature magazine conveyed good news. Two latest papers say that in 2018 and 2019, global Freon emissions once again showed a downward trend, and the emissions in eastern China in have been greatly reduced, accounting for as much as 60% of the total decline.
Ozone Killer
In 1973, Frank S. Rowland and Mario Molina from the University of California, Irving began to study the impact of Freon on the Earth's atmosphere. In their 1974 paper published in Nature , they pointed out that both CFC-11 and CFC-12 can exist stably in the atmosphere and are decomposed by ultraviolet radiation in the stratosphere many years later. The decomposition reaction "produces huge amounts of chlorine atoms," they wrote in the article, "and these chlorine atoms will eventually destroy the atmospheric ozone layer."
Roland and Molina won the 1995 Nobel Prize in Chemistry for Freon-related research. (Image source: Science History Institute)
The mechanism of chlorine atoms destroying the ozone layer is very simple. The chlorine atoms free in the ozone layer are very unstable and can react with ozone molecules and produce chlorine monoxide (ClO) and oxygen; chlorine monoxide can also react with ozone to re-form chlorine atoms and release oxygen. Therefore, chlorine atoms can initiate a vicious cycle in the ozone layer that lasts for about 2 years. In these two years, a chlorine atom alone can react with about 100,000 ozone molecules. Such a huge harm can quickly swallow ozone in the stratosphere: in the 1960s, the thickness of the ozone layer over Antarctica was 300 DU (Dobson unit [Note 2]); in 1985, the thickness of the ozone layer over Antarctica had dropped to 220 DU.
The Protocol brought unprecedented global solidarity: in 1988, the global Freon emissions were 1.46 million tons. After nearly 30 years of hard work, in 2014, global Freon emissions had dropped to 320,000 tons, and anthropogenic emissions were equivalent to natural emissions (about 160,000 tons each).
But since 2013, illegal emissions of CFC-11 have occurred in the coastal areas of northeastern China. The data comes from 12 atmospheric observatories distributed in North America, Europe, , Oceania, and remote Antarctica. These data show that between 2014 and 2017, the atmospheric concentration decline rate of CFC-11 slowed down significantly, dropping to half of the early 21st century. Moreover, the CFC-11 concentration gap in the northern and southern hemispheres has intensified unexpectedly, meaning that the CFC-11 emissions in the northern hemisphere far exceed expectations.
combined with the Hawaii Observatory and other Freon gas emission records, the researchers proposed that from 2008 to 2012, eastern China emitted 6,400 tons of CFC-11 in 4 years, while between 2014 and 2017, this figure reached 13,400 tons, an increase of nearly 110%. The newly added CFC-11 emissions of these accounted for 40% to 60% of the global total increase in the same period .
Remedial Action
In fact, China had already realized the seriousness of the problem as early as before the publication of two papers in 2018 and 2019 and took corresponding remedial measures. According to a report on in 2019 by the United Nations Environment Agency, China has strengthened supervision of freon production and emissions in 2018 and 2019. Although the first "Nature" paper in 2018 did not point the finger at China, after the paper was published, China quickly launched an action to combat the production and emission of ozone-depleting substances (ODS for short). According to China News Network, the Ministry of Ecology and Environment of carried out a special law enforcement inspection to combat ODS in August 2018, destroying two dens in Henan and Liaoning provinces that illegally produce CFC-11, and seized 177.6 tons of various production raw materials and 29.9 tons of illegally produced CFC-11 on the spot. This kind of action continues.
These new CFC-11 emissions are likely to come from closed-cell foam. Since the production process and foam itself contain CFC-11, CFC-11 emissions detected after 2010 may only account for 25% of the total new production volume. This means that during this period, the global Freon reserves have seen a sharp increase, reaching the level of 1 million to 2 million tons. Freon in reserves will leak slowly, which is the main reason for the slowdown in Freon concentration after 2013.
The good news is that these actions seem to have begun to show results. A study published in Nature recently collected and analyzed CFC-11 concentration data from two independent global detection networks (including NOAA network and the Global Advanced Atmospheric Gas Experiment Network). The analysis results show that in the second half of 2018 and early 2019, the rate of decline in CFC-11 concentration in the atmosphere increased significantly. Previous data showed that between 2014 and 2018, the CFC-11 concentration decreased by about 0.5% per year; between 2017 and 2018, this figure fell to 0.3%. However, between 2018 and 2019, the decline in CFC-11 concentration increased sharply, reaching 0.7%. What is even more gratifying is that in the nearly one year from the end of 2019 to the beginning of 2020, the decline in the atmospheric CFC-11 concentration of set a historical record, reaching 1.0% per year. At the same time, the study also used data from the Mauna Loa Observatory to confirm the source of CFC-11 emissions. The results show that among the global decline in CFC-11 emissions, the decline in eastern China was the most significant, accounting for as much as 60% of the total decline.
Another study published in Nature this Wednesday provided further evidence of a decline in CFC-11 emissions in eastern China. Data from South Korea's Gosan and Japan's Hateruma Observatory shows that CFC-11 emission levels in eastern China returned to pre-2013 levels in 2019. This means that between 2014 and 2017, the displacement of CFC-11 in eastern China decreased by about 100 million tons per year. At the same time, the displacement of carbon tetrachloride and CFC-12 also showed a significant decrease.
From left to right are the CFC-11 displacement heat maps of eastern China from 2008 to 2012, 2014 to 2017 and 2019. (Picture source: Park et al., Nature)
These latest results show that China's rapid Freon emissions crackdown has significant effects. But at the same time, the second paper also pointed out that compared with before 2013, in 2019, nearly 112,000 tons of CFC-11 reserves were added in eastern China, which was basically caused by China's sudden increase in CFC-11 production in the past decade. This also reminds us that the harm caused by the production and use of Freon is long-term and difficult to detect. To buy time for the recovery of the ozone layer, supervision must be carried out from the source.
[Note 1] "Freon" often refers to HCFC (CFC), but some reports refer to dichlorodifluoromethane (CFC-12), while others have expanded their scope, including other saturated hydrocarbon halogenates.
[Note 2] 1 Dobson unit is an ozone layer of 0.01 mm thick at standard temperature and standard pressure.
Written by: Luo Dinghao
