The decrease in ozone concentration in the middle layers of the atmosphere – mainly in the stratosphere – is extremely damaging to life on earth, and is largely caused by emissions of halogenated hydrocarbons produced by man, CFCs, HCFCs, halons, carbon tetrachloride and methyl bromide. For this reason, such substances are commonly referred to as Substances that Deplete the Ozone Layer (ODS).
The first warning voice came from a paper published in 1974 by scientists Sh. Rowland and M. Molina of the University of California, who showed that chlorofluorocarbons (CFCs) used in refrigeration, air conditioning and plastic foam manufacturing were responsible for the rapid destruction of ozone.
Ozone Destruction Mechanism
Substances such as CFCs, and others that are cited, that lower the ozone layer do not directly destroy ozone. First they undergo photolysis, forming hydrogen chloride (HCl) or chlorine nitrate (ClONO2), molecules that do not react with ozone directly, but slowly decompose, giving, among other things, a small number of chlorine atoms (Cl) and Of chlorine monoxide (ClO) molecules that catalyze the destruction of ozone.
The reactions involved in the processes of destruction are more than 100, but can be simplified in the following:
Cl + O 3 —–> ClO + O 2
ClO + O —–> Cl + O 2
Net effect: O 3 + O —–> 2 O 2
The chlorine atom acts as a catalyst, ie it is not consumed in the reaction, so it destroys thousands of ozone molecules before disappearing. The bromine atom is even more destructive than chlorine (about 10 or 100 times more). On the other hand, along with this, the chlorine concentrations are very low in the stratosphere and the bromine concentrations are even lower.
Cause of Ozone Layers Depletion
They are compounds formed by chlorine, fluorine and carbon. They are often used as refrigerants, solvents, and for the manufacture of spongy plastics. The most common are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115 which respectively have an ozone depletion potential of 1, 1, 0.8, 1, and 0.6.
Chlorofluocarbons, the chemicals used as the propellant for aerosol cans and Bromofluocarbons, Halon, are destroying the earth’s Ozone layer. These chemicals were used in Freon and for fighting fires. Manufactures thought the chemicals were inert and not harmful to the environment.
When the chemicals reached the earth’s stratosphere, they reacted with Ultraviolet radiation, which caused them to break down and release Chlorine and Bromine into the earth’s ozone layer. The Ozone layer protects the earth from UV-B Rays. The chemicals caused a reaction, which made the ozone layer break down into pure oxygen. The layer lost its shielding effect from the suns UV rays. The Bromine and Chlorine kept interacting with the ozone molecules until they eventually left the ozone layer to bond with other compounds.
Compounds formed by H, Cl, F and C. They are being used as substitutes for CFCs because many of their properties are similar and are less harmful to ozone by having a shorter half-life and releasing fewer Cl atoms. Decreases are between 0.01 and 0.1. But as they remain harmful to the ozone layer, they are considered only a temporary solution and their use has been banned in developed countries since the year 1930.
They are compounds formed by Br, F and C. Because of their ability to put out fires are used in fire extinguishers, although their manufacture and use is prohibited in many countries because of their ozone-depleting action. Their ability to harm the ozone layer is very high because they contain Br which is a much more effective atom destroying ozone than the Cl. Thus, halon 1301 and halon 1211 have ozone depletion potentials of 13 and 4 respectively.
Note: Technically all compounds containing C and F and / or Cl are halons, but in many legislation halon only means fire extinguishing substances with the characteristics indicated above.
Methyl bromide (CH3Br)
It is a very effective pesticide that is used to fumigate soils and in many crops. Given its content in Br damages the ozone layer and has an ozone depletion potential of 0.6. In many countries dates have been set around 2000, from which it will be banned.
Carbon tetra-chloride (CCl4)
It is a compound that has been widely used as a raw material in many industries, for example, to manufacture CFCs and as a solvent. It was no longer used as a solvent when it was found to be carcinogenic. It is also used as catalysts in certain processes where chlorine ions need to be released. Its ozone depletion potential is 1.2.
Effects of Ozone Layers
1. Effects of the depletion of the ozone layer on human health
1.1 Skin Cancer
Today, it is estimated that skin cancer rates increased due to the decrease in stratospheric ozone (ozone layer). The most common type of skin cancer, called non-melanoma, is the cause of exposures to UV-B radiation for several years. There are already people who have received the dose of UV-B that can cause this type of cancer.
The United Nations Environment Program (UNEP) predicts that at an annual rate of 10 percent ozone loss over several decades, the increase in skin cancer will be around 250,000 per year. Even taking into account existing agreements for the phase-out of ozone-depleting substances (ODS), a realistic model would indicate that skin cancer would increase to 25 percent above the level of 1980 by the year 2050, along Of the 50 ° North latitude. The most lethal skin cancer, called melanoma, could also increase its frequency.
1.2 The Immune System
A person’s defenses against infection depends on the strength of his immune system. It is known that exposure to ultraviolet light reduces the effectiveness of the immune system, not only relating to infections to the skin but also to those that can be verified in other parts of the body.
Exposure to UV-B radiation may well enable the immune system to tolerate disease rather than combat it. This could mean the uselessness of vaccination programs in both industrialized and developing countries.
2. Effects on aquatic ecosystems
The loss of phytoplankton, the basis of the marine food chain, has been observed as the cause of the increase in ultraviolet radiation. Under the ozone hole in the Antarctic phytoplankton productivity decreased between 6 and 12 percent.
UNEP indicates that a 16 percent decrease in ozone could result in a 5 percent loss of phytoplankton, which would mean a loss of 7 million tonnes of fish per year – around 7 percent of global fish production. 30 percent of human consumption of protein comes from the sea, this proportion increases even more in the developing countries.
3. Effects on terrestrial ecosystems
For some species, an increase in UV-B radiation implies the formation of skin cancer. This has been studied in goats, cows, cats, dogs, sheep and laboratory animals and is probably pointing out that this is a common feature of several species. Infections in cattle can be aggravated by an increase in UV-B radiation. 3.2 Plants In many plants UV-B radiation can have the following adverse effects: alter its shape and damage plant growth; Reduce tree growth; Change flowering times; Make plants more vulnerable to disease and produce toxic substances. There could even be losses of biodiversity and species.
- Replace halon-based fire extinguishers with others using foam.
- Check on the label of the products, which we buy at the supermarket, to report that they do not damage the ozone layer.
- Use your car only when necessary. The less we use our cars, the less pollutants we will emit into the atmosphere. Remember that burning fossil fuels breeds many substances that damage the ozone layer.
- Do not buy refrigerators or air conditioner equipment that use CFCs as refrigerant. Look for this information in the labels, or ask the supplier of the product directly.
- Do not use cleaning solvents containing CFCs or ammonia.
- Do not use sprays, and do not buy objects made of plastic foam (dry ice or freezer). If you receive these products as a fill of your mail packages, return them immediately to the sender. Low consumption of these products will discourage plastic foam manufacturers.
- Make yourself heard. Please show this page to your children, relatives, friends and neighbors.
The Ozone layer is improving since the Montreal Protocol came into effect to stop and control the use of these chemicals. The Ozone layer depends on UV-C rays from the sun to replenish its self. The contaminants from chemicals prevent it from getting what it needs to protect the earth from harmful UV-B Rays
The Ozone layer is improving, but it will need many years before it the damage is repaired.
The ozone hole over the Antarctic has begun to heal, according to a new study, more than 30 years after its discovery. The findings suggest that global efforts to phase out ozone-depleting chemicals have been effective, though scientists still aren't entirely sure about what's driving the ozone hole's recovery.
The study, published in the journal Science, combines data gathered from balloons and satellites to measure the area of the ozone layer over Antarctica from 2000 to 2015. Since 2000, the paper reports, the size of the ozone hole over Antarctica shrank by about 4 million square kilometers — an area equivalent to about half of the contiguous United States. Using computer simulations to account for changes in wind and temperature, the study's authors estimate that about half of its reduction can be attributed to a decline in levels of the ozone-depleting gases chlorine and bromine.
The stratospheric ozone layer protects Earth from the sun's harmful ultraviolet (UV-B) rays, which can cause skin cancer and cataracts in humans, and physiological damage in animals and plants. Faced with growing evidence of ozone depletion, governments in 1987 ratified the Montreal Protocol, a global treaty that aimed to phase out the production of harmful chemicals known as chlorofluorocarbons (CFCs). At the time, CFCs were used in hairspray, aerosol cans, and refrigerators. A single CFC molecule can last for between 20 and 100 years in the atmosphere, and can destroy100,000 ozone molecules.
Previous studies have shown that the rate of ozone depletion has declined since the Montreal Protocol went into effect, and a 2014 United Nations report showed that Earth's ozone layer has begun to heal. But the ozone hole over the Antarctic reached a record size in 2015, casting some doubt over claims of a recovery, and the UN report said it was still unclear whether healing in the Antarctic could be attributed to a decline in ozone-depleting gases. Susan Solomon, professor of atmospheric chemistry and climate science at MIT and lead author of the study published this week, says her findings suggest that the Montreal Protocol has in fact worked.
"We are beginning to see clear signs that actions that society took to phase out chlorofluorocarbons are actually having the intended effect of beginning to heal the Antarctic ozone layer," Solomon says, stressing that the recovery is still in its early phases. "It's really a remarkable achievement for society," she adds. "It's a global environmental problem, and we have put ourselves on a good trajectory."
The ozone hole appears over Antarctica every year and is usually at its largest during October, as the continent transitions from winter to summer. Previous studies used that month as a benchmark for measuring the hole's size, but Solomon and her colleagues focused instead on September because the Antarctic weather is historically less variable, making it easier to isolate the effect of chlorine and bromine, which deplete ozone. In the process, they found that the Antarctic ozone hole is opening later in the year, another sign that it is healing. They also found that seemingly anomalous observations of very large holes, as in 2015, could be attributed to volcanic eruptions, which deplete ozone by releasing sulfates into the atmosphere.A satellite image of the ozone hole over Antarctica in October 2015, when it was at its largest. (NASA)
Paul A. Newman, chief scientist for atmospheric sciences at NASA's Goddard Space Flight Center, says the study raises important questions about what else is driving the recovery of Antarctica's ozone hole besides the decline in chlorine and bromine. He notes that the paper's ozone measurements still show a high level of variability, which Solomon and her colleagues attribute to weather effects. The authors say there is likely some interplay between declining chlorine levels and changes in Antarctic weather, though they have yet to quantify that relationship.
"You have to be able to explain the causes of the total trend," says Newman, who was not involved in the study. "Not just the half due to the ozone depleting substances."
Still, Newman believes that the study's findings provide further proof that experts were correct in sounding the alarm over ozone levels during the 1970s and 1980s. "We predicted this way back in the day — we scientists said this would happen, and we said that if you do something, things will eventually get better," he says. "And so this is the kind of thing that we've been looking for."
But the Montreal Protocol has had some negative consequences, as well. When countries began phasing out CFCs, manufacturers replaced them with hydrofluorocarbons (HFCs). HFCs don't deplete ozone, but they are potent greenhouse gases, which contribute to global warming. The challenge going forward, then, will be to develop new alternatives to HFCs — and to have the world adopt them, once again.
"That's going to be really interesting to see if the diplomatic community can manage that," Solomon says. "And what the technology community can do in terms of developing alternatives is obviously going to be very important."
Jonathan Shanklin, a meteorologist at the British Antarctic Survey, was one of three scientists who discovered the ozone hole over Antarctica in 1985. Their discovery spurred world leaders to ratify the Montreal Protocol two years later, and every country in the UN has now signed on to it. He says Solomon's findings are further proof that the treaty has been "astonishingly successful," though he never imagined that the work he did 30 years ago would lead to it.
"At the start, I didn't really think it was a terribly significant discovery," Shanklin says. "I thought it was some obscure fact of Antarctic meteorology and it might be interesting scientifically, but that would be the end of it."
"It has been really astonishing to me that that little discovery has unified the world's countries to really produce a measurable effect. And I only wish that they could unify in the same way over the many issues that affect the climate today."
Correction 3:10pm ET: A previous version of this article stated that the Ozone hole over Antarctica had shrunk by 4 million square miles. The correct measurement is in kilometers. The piece has been updated.