Planet Earth has its own natural sunscreen that shields us from the sun's damaging ultraviolet radiation. It's called the ozone layer: a fragile band of gases beginning 15 kilometres above our planet, and reaching up to the 40-kilometre level. Human activities have caused a substantial thinning of this protective covering not only over the North and South Poles, but right over our heads. Stopping ozone layer depletion is one of the major challenges facing the world today. The stakes are incredibly high. For the ozone layer is truly a protector of life essential to the survival of all living things.
The ozone layer lies in the stratosphere, in the upper level of our atmosphere. Stratospheric ozone filters out most of the sun's potentially harmful shortwave ultraviolet (UV) radiation. This ozone has become depleted, due to the release of such ozone-depleting substances as chlorofluorocarbons (CFCs). When stratospheric ozone is depleted, more UV rays reach the earth. Exposure to higher amounts of UV radiation could have serious impacts on human beings, animals and plants.
Ozone is a gas made up of combining three atoms of Oxygen. It usually acts as a protective shield for the earth and the environment and protects it from the dangerous ultra-violet rays of the sun. Life forms cannot survive without the ozone layer because the ozone layer protects us from harmful ultraviolet rays that radiate from the sun. These rays can cause cancer, damage to crops and threat to marine organisms. Chlorine and bromine molecules are responsible for the degradation of the ozone layer. When gases containing these molecules are released into the environment, they cause erosion of the ozone layer over time. The most common halogen gas that damages ozone is chloro-fluoro carbon, also known as CFC. Talking about the efforts being made to save it, first of all it is necessary that people are aware about the ozone layer and its protection. There are several easy methods that can protect the ozone layer such as using eco-friendly products, avoiding the use of aerosols and other CFC containing things, promoting plantation.
In 1785, researchers working with early, arcing electrical discharge devices had noted ozone's peculiar odor. The word ozone is in fact derived from the Greek ozein, meaning "to smell." In 1872, scientists determined that ozone was a triatomic form of oxygen, or 03. As a concentrated gas, ozone is pale blue, carries a strong odor, and is highly poisonous.
ozone's three oxygen atoms form an enormous molecular triangle. Because of weak atomic bonding between the distant atoms, ozone is a very unstable molecule that quickly dissociates into common oxygen and a free oxygen atom (0) called atomic oxygen. The ability to release atomic oxygen makes ozone a powerful oxidizing agent, or giver of oxygen to other molecules. In contrast, common oxygen is two oxygen atoms held together by strong bonds that produce the stable oxygen molecules. Common oxygen makes up 20 percent of our atmosphere.
Ozone forms naturally in the lower levels of the atmosphere when the electrical arcs of lightning pass through oxygen molecules. After it is formed in the atmosphere, ozone survives only about 20 minutes before it dissociates. Most of Earth's natural ozone, however, is formed in the stratosphere, the upper portion of the atmosphere. There, at an altitude of about 15 miles, photochemical reactions driven by intense solar ultraviolet radiation both create and destroy ozone.
High-energy ultraviolet rays split common oxygen molecules into free oxygen atoms, some of which combine with common oxygen molecules to form ozone. Simultaneously, low-energy ultraviolet radiation splits ozone into common oxygen and free oxygen atoms. Each free oxygen atom may then combine with common oxygen to create more ozone, or it may join with another oxygen atom to form common oxygen. Ozone can also react with nitrogen and hydrogen, and as well with chlorine, trace amounts of which originate naturally in soils, oceans, and volcanic eruptions and migrate into the stratosphere. Given the multitude of factors, especially the solar cycle and variations in stratospheric winds affecting the formation and lifetime of stratospheric ozone, its concentration and extent varies periodically.
Scientific evidence indicates that stratospheric ozone is being destroyed by a group of manufactured chemicals, containing chlorine and/or bromine. These chemicals are called ozone-depleting substances" (ODS). ODS are very stable, nontoxic and environmentally safe in the lower atmosphere, which is why they became so popular in the first place. However, their very stability allows them to float up, intact, to the stratosphere. Once there, they are broken apart by the intense ultraviolet light, releasing chlorine and bromine. Chlorine and bromine demolish ozone at an alarming rate, by stripping an atom from the ozone molecule. A single molecule of chlorine can break apart thousands of molecules of ozone. ODS have a long lifetime in our atmosphere- up to several centuries. This means most of the ODS we've released over the last 80 years are still making their way to the stratosphere, where they will add to the ozone destruction.
The main ODS are chlorofluorocarbons (CFCs), hydrochlorofluorcarbons (HCFCs), carbon tetrachloride and methyl chloroform. Halons (brominated fluorocarbons) also play a large role. Their application is quite limited: they're used in specialized fire extinguishers. But the problem with halons is they can destroy up to 10 times as much ozone as CFCs can. For this reason, halons are the most serious ozone-depleting group of chemicals emitted in British Columbia.
Hydrofluorocarbons (HFCs) are being developed to replace CFCs and HCFCs, for uses such as vehicle air conditioning. HFCS do not deplete ozone, but they are strong greenhouse gases. CFCs are even more powerful contributors to global climate change, though, so HFCs are still the better option until even safer substitutes are discovered.
Dramatic loss of ozone in the lower stratosphere over Antarctica was first noticed in the 1970s by a research group from the British Antarctic Survey (BAS) who were monitoring the atmosphere above Antarctica from a research station. Folklore has it that when the first measurements were taken in 1975, the drop in ozone levels in the stratosphere was so dramatic that at first, the scientists thought their instruments were faulty. Replacement instruments were built and flown out and it wasn't until they confirmed the earlier measurements, several months later, that the ozone depletion observed was accepted as genuine. Another story goes that the BAS satellite data didn't show the dramatic loss of ozone because the software processing the raw ozone data from the satellite was programmed to treat very low values of ozone as bad readings. Later analysis of the raw data when the results from the British Antarctic Survey team were published, confirmed their results and showed that the loss was rapid and large-scale; over most of the Antarctica continent.
The depletion of the ozone layer does not come without problems. Scientific research has suggested the probability that increased UV-B radiation as a result of the thinning ozone layer leads to increased cases of skin cancer, immuno-suppression, cataracts, and snow blindness due to radiation damage of the DNA. Additionally, experiments have shown a correlation between increased UV radiation and crop damage due to UV radiation damaging the plants DNA. Some scientists, however, feel that this will not be a problem in the future due to the possibility of breeding UV resistant crops and plants.
