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Environmental Quality Branch STRATOSPHERIC OZONE DEPLETION Stratospheric Ozone Depletion June 2008 Introduction 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 "conserver of life," essential to the survival of all living things.
The ozone layer lies in the stratosphere, in the upper level of our atmosphere. The ozone in it is spread very sparsely. In fact, if you could squish the ozone layer to the same air pressure we have at sea level, it would be only about as thick as the sole of your shoe. Stratospheric ozone filters out most of the sun's potentially harmful shortwave ultraviolet (UV) radiation. If this ozone becomes depleted, then more UV rays will reach the earth. Exposure to higher amounts of UV radiation could have serious impacts on human beings, animals and plants, such as the following:
The stratospheric ozone layer sometimes gets confused with the ozone lying near the earth's surface, known as "ground-level ozone." Although some ground-level ozone occurs naturally, most is produced by the reaction of sunlight with chemicals found mainly in automobile exhaust and gasoline vapours. This human-caused ozone is a key, unhealthy ingredient of smog. Ironically, we have too much ozone at ground level and not enough in the stratosphere — and there's no practical way of moving it.
Current evidence indicates that stratospheric ozone is being destroyed, largely by a group of manufactured compounds called chlorofluorocarbons (CFCs). CFCs were invented in the 1920s, and used in all sorts of everyday products — for the coolant in refrigerators and air conditioners, flexible foam in furniture, and rigid foam in insulation. But it wasn't until the mid-'70s that scientists discovered CFCs' Jekyll-and-Hyde nature. CFCs are very stable, nontoxic and environmentally safe in the lower atmosphere, which is why they became so popular in the first place. However, CFCs' very stability allows them to float up, intact, to the stratosphere. Once there, they wreak havoc on the ozone layer. And that is the case for all the ozone-depleting substances (ODS).
When CFCs and other ODS reach the stratosphere they are broken apart by the intense ultraviolet light, releasing chlorine and bromine. The 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. What's more, CFCs have a long lifetime in our atmosphere — up to several centuries. This means most of the CFCs we've released over the last 80 years are still making their way to the stratosphere, where they will add to the ozone destruction. CFCs are the main chemicals eating away at the ozone layer, but not the only ones. Halons (brominated fluorocarbons) also play a large role. Their application is quite limited compared to CFCs: they're used in specialized fire extinguishers. But the problem with halons is they can destroy up to 16 times as much ozone as CFCs can. For this reason, halons are the most serious ozone-depleting group of chemicals emitted in British Columbia. Methyl chloroform and carbon tetrachloride trigger stratospheric ozone depletion, too. Even some of the new "replacement chemicals" for CFCs will be somewhat destructive of the ozone layer.
Halons Used in some fire extinguishers, in cases where materials and equipment would be destroyed by water or other fire extinguisher chemicals. In B.C., halons cause greater damage to the ozone layer than do CFCs from automobile air conditioners. Methyl Chloroform
Carbon Tetrachloride
In 1985, a group of scientists made an unsettling discovery: a marked decrease in stratospheric ozone over the South Pole, in the Antarctic. The "hole" appeared during the southern hemisphere's spring (October and November) and then filled in. The problem isn't confined to the southern hemisphere, though. It's happening right on top of us, in the north. Soon after the antarctic hole was found, Canadian scientists discovered that the ozone layer above the Arctic is also thinning significantly. The highest latitudes — the north and south poles — experience the greatest amount of ozone loss, during their spring. Ozone depletion is most pronounced in the Antarctic. But ozone depletion, to a lesser degree, now occurs in the mid-latitudes. For example, the amount of stratospheric ozone over the northern hemisphere has been dropping by 4% per decade. What does this mean for life on earth? Even the smallest reduction in stratospheric ozone can have a noticeable impact by increasing the amount of UV radiation that reaches the planet. Studies show, for example, that a decrease in stratospheric ozone could cause additional deaths from skin cancer. Even a 1% global reduction in ozone is expected to cause a significant drop in crop yields, in a world that is already struggling to feed itself.
193 nations, including Canada, have signed an international agreement to end the production of CFCs, halons and other ODS, called the Montreal Protocol on Substances that Deplete the Ozone Layer (1987). The protocol has been amended several times, to speed up ODS phaseout dates and to include more types of ozone-depleting substances. Canada has adopted a national action plan to meet the requirements of the Montreal Protocol, which includes regulations and codes of practice to control the import, manufacture, use, sale and export of ODS. Here in B.C., the provincial government passed a regulation in 1993 to control ozone-depleting substances (ODS) stored in products and equipment, and encourage consumers and industry to use environmentally safe alternatives. Originally called the Ozone Depleting Substances Regulation, the regulation covered all CFCs, halons and HCFCs, as well as methyl chloroform and carbon tetrachloride. The regulation was amended in November 1999, mainly to include HFCs and PCFs, and strengthen certain requirements. It was renamed the Ozone Depleting Substances and Other Halocarbons Regulation. The regulation was amended again in 2004, largely to add more CFC-refill restrictions for the refrigeration sectors, refill restrictions for halon fire extinguishers and revised seller take-back provisions for surplus CFC refrigerators. A minor wording change was made in 2006. For more information, see Amendments to the Ozone Depleting Substances and Other Halocarbons Regulation.
To make sure ODS are recovered correctly, technicians working with these chemicals must have completed an ODS environmental awareness course approved by Environment Canada and the ministry. B.C. no longer allows the recharging of a motor vehicle air conditioner (MVAC) with CFC-12, the common refrigerant in older air conditioners. Instead, a non-ODS alternative is necessary. Also, anyone servicing an MVAC system must have successfully completed an MVAC servicing-and-retrofitting course approved by the ministry. A 1997 study carried out for Environment Canada found that the benefits of meeting the Montreal Protocol targets will far outweigh the costs. For the period between 1987 and 2060, the study estimates the Montreal Protocol will result in net monetary benefits of $224 billion. This figure does not include the health benefits (for which a dollar cost is harder to determine): the prevention of over 20 million cases of skin cancer, 129 million cases of cataracts and over 333 thousand deaths.
The nations of the world have taken a crucial step in joining together to halt the production and use of ozone-destroying chemicals. But the work can't stop there. As individuals, we also contribute to the problem. Now it's time to become part of the solution. Here's what you can do:
Will we be able to halt stratospheric ozone depletion before it's too late? Because of the long survival rate of CFCs and other ozone-depleting substance, ozone destruction will persist through the 21st century and well into the 22nd century, no matter how fast we eliminate the compounds on earth. The severity of the ozone layer damage will also depend on how well we recover and recycle the ozone-depleting substances that are "banked" in existing products. However, if we all make the effort to reduce, recover, reuse and recycle ODS, we can be fairly confident that, one day, the ozone layer will be able to rebuild itself to its former strength. Ozone is naturally produced in the atmosphere. Therefore, once the ODS-derived chlorine and bromine are finally gone, the stratospheric ozone will gradually reach the concentrations that existed before CFCs and their counterparts came along. Even though we won't be around in the 22nd century to see how the ozone layer has fared, we have a strong link with the people of that time and a deep responsibility to them. For the future health of the ozone layer — the planet's precious sunscreen — depends on how each one of us cares for it today.
Environmental Quality Branch PO Box 9341, Stn Prov Govt | ||||
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