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Posted on: December 21, 2020

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Whatever Happened to… the Ozone Layer Hole? | OpenMind


When researchers Frank Sherwood Rowland and Mario Molina told the world in 1974 that aerosol hairsprays damaged the part of the atmosphere that protects us from solar ultraviolet radiation, the reactions were not simply disbelief: a senior chemist at DuPont called the theory a “science fiction tale,” “a load of rubbish” and “utter nonsense.”

However, soon after, the so-called ozone hole became not only a global concern, but also one of the symbols of the green activism of the 1980s. The rapid reaction to tackle the problem by banning harmful compounds represents the greatest success achieved by an international environmental agreement. But it is also an example of how technological progress is seeking more sustainable solutions to the problems that technological progress itself has caused.

The success of Rowland and Molina, chemists at the University of California, Irvine, was to piece together ideas that had gone unnoticed by others. In the early 1970s, it was known that chlorine and other substances can catalyse the destruction of ozone, a compound composed of three oxygen atoms that is present in a greater proportion in a layer of the earth’s stratosphere, and which blocks much of the harmful UV radiation. However, no one had linked this phenomenon to chlorofluorocarbons (CFCs), gases that began to be produced industrially in the 1930s and were used extensively as aerosol propellants, refrigerants and to make plastic foams. CFCs are inert and long-lived, so they can remain in the atmosphere for decades. Rowland and Molina theorized that the breakdown of CFCs by sunlight releases chlorine, which could result in significant damage to the ozone layer.

Despite the initial negative reaction to the study by the two chemists, subsequent experiments and atmospheric measurements soon confirmed that they were correct. In 1985, a study by the British Antarctic Survey discovered something that surprised the scientific community, a particularly sharp decline in ozone concentration over Antarctica, when the decline was expected to be equally distributed across the planet. The following year, US National Oceanic and Atmospheric Administration (NOAA) researcher Susan Solomon provided the explanation: the cold winter temperatures at the poles form stratospheric polar clouds, which encourage the breakdown of CFCs and other halocarbons —composed of carbon and halogen elements such as chlorine, fluorine, bromine or iodine— generating more free chlorine, which in the southern spring accentuates the destruction of ozone.

The scientific consensus on the ozone hole led some countries to adopt unilateral measures, and in 1987 a total of 46 nations signed the Montreal Protocol, aimed at phasing out the production of ozone-depleting substances. However, industry was still reluctant to throw in the towel; in 1988, DuPont’s president, Richard Heckert, wrote to the U.S. Senate: “At the moment, scientific evidence does not point to the need for dramatic CFC emission reductions. There is no available measure of the contribution of CFCs to any observed ozone change.”

The Montreal Protocol, in force since 1989, is often regarded as the most successful international environmental agreement in history. In fact, according to the UN, to date it is the only UN treaty that has been ratified by all the countries on the planet, all 197 member states. On a transitional basis, CFCs have been replaced by hydrochlorofluorocarbons (HCFCs), which are supposed to be less harmful to the ozone layer, with the aim of replacing them entirely with hydrofluorocarbons (HFCs) and other compounds. These are more unstable in the lower atmosphere, so their impact on stratospheric ozone is assumed to be low or zero. Thanks to the reduction of CFCs, since 2005 ozone destruction has decreased by 20%, according to NASA, and the hole is expected to disappear almost completely between 2060 and 2080.

But the implications are more complex: in addition to their effect on ozone, CFCs are also much more powerful greenhouse gases than CO2. A recent study conducted by Columbia University (USA) atmospheric and climate dynamics expert Lorenzo Polvani has determined that ozone-depleting substances such as CFCs have been responsible for half of the warming of the Arctic and the melting of North Pole ice during the second half of the 20th century. “Banning of CFCs by the Montreal Protocol will mitigate Arctic warming and sea ice loss in the coming decades,” Polvani told OpenMind, although he made it clear that the overall trend will not be reversed without the necessary reductions in CO2, the main culprit in climate change.

One problem is that alternative solutions to CFCs must not only be more sustainable, but also economically viable. In 2018, a team led by NOAA researcher Stephen Montzka discovered an unexpected 25% increase in emissions of CFC-11 (the second most abundant CFC) starting from 2012, slowing the decline in the concentration of this gas by 50%, and this despite the fact that the Montreal Protocol established the cessation of global production by 2010. “We identified China as being responsible for about half of that global emissions increase,” Montzka told OpenMind. The researcher notes that studies are still under way to determine the causes and impact of this clear violation of the international agreement, but some experts suggest that perhaps the alternatives to CFCs could be too expensive or unaffordable for some countries.

There is also another complication: ozone-friendly HFCs also contribute to climate change. Recently, researchers have detected an increase in emissions of HFC-23, the greatest cause of global warming among HFCs and a compound that should have been drastically reduced under the current version of the Montreal Protocol. In short, finding a practical way to cool ourselves and propel our aerosols without destroying the ozone layer or aggravating climate change is still an ongoing technological challenge.

Javier Yanes

Montreal Protocol คืออะไร... - วิศวกรรมสิ่งแวดล้อม ม.เอเชียอาคเนย์ |  Facebook


  1. The background to the Rowland Molina theory of ozone depletion (RMTOD) is that since 1969 multiple failed theories of ozone depletion were proposed with claims that supersonic airliners, the space shuttle, and various other technologies being proposed would cause ozone depletion with blindness and skin cancer epidemics. RMTOD was simply the latest in that line of an obsession with ozone depletion fearology and it can only be understood in that context.
  2. RMTOD 1974 is not a work in isolation that can be accredited solely to Rowland and Molina. Firstly, as explained above, it was just yet another ozone depletion fear in a long line of ozone depletion fears since 1969. Even more important is that RMTOD is a product of the Lovelock 1973 paper. In 1973 James Lovelock discovered that air samples taken from the Middle of the Atlantic Ocean contained CFCs. He then published his now famous paper in which he said that these man made chemicals that did not otherwise occur in nature were inert and could therefore accumulate in the atmosphere indefinitely. It was from this work that Rowland and Molina surmised that given enough time, maybe 40 to 100 years, the inert and long lived CFCs could, by random molecular movement, end up in the stratosphere where they could be disintegrated by UV radiation to produce radical agents of ozone destruction. What Rowland and Molina proved in their lab is that UV radiation would indeed break down the CFCs and that the radicals thus produced would indeed destroy ozone but no evidence has every been produced and none exists that CFCs did indeed end up in the stratosphere. That part of RMTOD is simply imagined in a “What If” logic.
  3. The only empirical evidence presented in support of RMTOD is Farman etal 1985. The Farman study showed only that there was a brief and localized 5-year period of low ozone in the months of October and November above the South Pole that had recovered to normal levels and this was taken as evidence of RMTOD. Yet, this episodal and localized low ozone event does not serve as evidence of the RMTOD theory of ozone depletion. This theory implies a long term declining trend in global mean total column ozone. No evidence for this trend has ever been presented and we show in a related post that none exists. LINK: .
  4. Instead, the South Polar periodic low ozone event that quickly recovers back to normal levels was sold to the general public as an “ozone hole” and claimed as evidence of RMTOD human caused global ozone depletion that could cause skin cancer in humans and blindness in animals up in North America. Then at some point, it was declared with great fanfare that the UN brokered Montreal Protocol had solved the ozone depletion problem and that the ozone had recovered. No explanation is offered for the continuation of these South Polar ozone events that had been named ozone holes.
  5. In a related post LINK: we show that these South Polar events should be understood as ozone distribution events and not ozone depletion. Ozone is both created and destroyed by UV radiation. Ozone is created only above the Tropics where sunlight is direct and distributed to the greater latitudes by the Brewer Dobson circulation and episodic changes in ozone levels at the higher latitudes can be understood in terms of the dynamics of this distribution but not in terms of long term ozone depletion due to the presence of ozone depleting substances in the stratosphere.
  6. The only significant impact of what is claimed to be finally a proven case of ozone depletion after all those failures is that it served to expand the role of the UN into global environmentalism.
Largest-ever hole in the ozone layer above Arctic finally closes | Euronews
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Ozone layer
From Wikipedia, the free encyclopedia

“Ozone-oxygen cycle in the ozone layer.
The ozone layer or ozone shield is a region of Earth’s stratosphere that absorbs most of the Sun’s ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 to 35 kilometers (9.3 to 21.7 mi) above Earth, although its thickness varies seasonally and geographically.[1]

The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Measurements of the sun showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the spectrum of a black body with a temperature in the range of 5,500–6,000 K (5,227 to 5,727 °C), except that there was no radiation below a wavelength of about 310 nm at the ultraviolet end of the spectrum. It was deduced that the missing radiation was being absorbed by something in the atmosphere. Eventually the spectrum of the missing radiation was matched to only one known chemical, ozone.[2] Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson established a worldwide network of ozone monitoring stations, which continue to operate to this day. The “Dobson unit”, a convenient measure of the amount of ozone overhead, is named in his honor.

The ozone layer absorbs 97 to 99 percent of the Sun’s medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength), which otherwise would potentially damage exposed life forms near the surface.[3]”

The comment:

“The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth’s atmosphere as a whole is about 0.3 parts per million.”

“Measurements of the sun showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the spectrum of a black body with a temperature in the range of 5,500–6,000 K (5,227 to 5,727 °C), except that there was no radiation below a wavelength of about 310 nm at the ultraviolet end of the spectrum. It was deduced that the missing radiation was being absorbed by something in the atmosphere.”

There was no radiation below a wavelength of about 310 nm at the ultraviolet end of the spectrum.

So it was deduced… that the missing radiation was being absorbed by something in the atmosphere.

“About 90 percent of the ozone in the atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40 kilometers (66,000 and 131,000 ft), where they range from about 2 to 8 parts per million. If all of the ozone were compressed to the pressure of the air at sea level, it would be only 3 millimeters (1⁄8 inch) thick. [6]” ”

“Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the sun. Extremely short or vacuum UV (10–100 nm) is screened out by nitrogen. UV radiation capable of penetrating nitrogen is divided into three categories, based on its wavelength; these are referred to as UV-A (400–315 nm), UV-B (315–280 nm), and UV-C (280–100 nm).
UV-C, which is very harmful to all living things, is entirely screened out by a combination of dioxygen ( about 200 nm) by around 35 kilometres (115,000 ft) altitude. UV-B radiation can be harmful to the skin and is the main cause of sunburn; excessive exposure can also cause cataracts, immune system suppression, and genetic damage, resulting in problems such as skin cancer. The ozone layer (which absorbs from about 200 nm to 310 nm with a maximal absorption at about 250 nm)[7] is very effective at screening out UV-B; for radiation with a wavelength of 290 nm, the intensity at the top of the atmosphere is 350 million times stronger than at the Earth’s surface. Nevertheless, some UV-B, particularly at its longest wavelengths, reaches the surface, and is important for the skin’s production of vitamin D.
Ozone is transparent to most UV-A, so most of this longer-wavelength UV radiation reaches the surface, and it constitutes most of the UV reaching the Earth. This type of UV radiation is significantly less harmful to DNA, although it may still potentially cause physical damage, premature aging of the skin, indirect genetic damage, and skin cancer.[8]”

“the intensity at the top of the atmosphere is 350 million times stronger than at the Earth’s surface.”

The ozone layer contains less than 10 parts per million of ozone.
So 10 ppm of ozone in ozone layer, in the stratosphere, where the atmosphere is very much thinner than at the Earth’s surface…
This 10 ppm of ozone in ozone layer screen out UV-B 350 million times stronger than at the Earth’s surface.

When science accepted that, it was very easy then to make the next step and accept that the 400 ppm CO2 may cause a major greenhouse warming effect on Earth’s surface.

Here is the grapheme with the deduced sun’s UV radiation.

Here is the grapheme illustrating the sun’s UV emission compared to the blackbody curve of the same energy intensity.

Thank you for your comment.

Suppose it had nothing to do with dupont’s expiration of the patent it had on the r12. 80% was manufactured in the US at that time. Then the 80% switched to offshore.
Doesn’t volcanic action create the same reaction in the atmosphere.

Interesting point. Thank you.

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