Ecology: Biology of Interactions. 6.10. Ozone and Ozone-Layer Depletion
In 1985, an "ozone hole" was discovered above the South Pole (a zone where ozone content was 40-50% of normal). According to the most probable hypotheses, its formation is linked to freons (chlorofluorocarbons).
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6.09. Global Warming
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 6. Human Ecology and Conservation
6.11. Acid Rain
6.10. Ozone and Ozone-Layer Depletion Under the influence of ionizing radiation, an oxygen molecule (O2) can split into atomic oxygen, which, joining other oxygen molecules, forms ozone (O3). Ozone absorbs ionizing radiation (from far ultraviolet with wavelengths from 315 nm to gamma rays) much better than oxygen. As a result, in the upper atmosphere (from 12-25 to 45 km above Earth's surface) a layer with elevated ozone content is formed (concentration about 0.001%). Owing to this layer, the dose of ionizing radiation reaching Earth's surface decreases sharply. Ozone is a gas that is sometimes present at the planet's surface as well. It is responsible for the smell of "freshness" after a thunderstorm. It can be detected near operating ultraviolet lamps, and also near malfunctioning laser printers and photocopiers. At Earth's surface, ozone is a dangerous pollutant. Its danger is due both to it being a much stronger oxidant than oxygen (and therefore capable of damaging living cells, for example causing lung cancer), and to its ability to participate in transformations of other atmospheric pollutants. In 1985, an "ozone hole" was discovered above the South Pole (a zone with ozone content within 40-50% of normal), with an area comparable to the territory of the USA. According to the most probable hypothesis, its formation is linked to freons (chlorofluorocarbons). These substances are used in refrigeration units, aerosol cans, plastic foaming, and cleaning of computer microchips. Released into the atmosphere, freons reach the upper boundary of the ozone layer in 10-20 years, where under ionizing radiation they decompose, forming atomic chlorine and fluorine. Reacting with ozone molecules, fluorine and chlorine trigger a chain reaction of ozone destruction. This effect is especially strong at low temperatures (which is why the ozone hole formed over Antarctica). At present, "ozone holes" are considered regions where ozone content is reduced by 30% relative to normal. In October 2000, the ozone hole over Antarctica reached 29.53 million km2. Its zone of influence had already reached the Chilean city of Punta Arenas, and New Zealand, Argentina, Australia, and South Africa were under threat. Under the ozone hole, a substantial increase in ultraviolet radiation reaching Earth's surface has been recorded, including not only near UV (UV-A, wavelength 400-315 nm), but also far UV (UV-B, wavelength 315-280 nm, and UV-C, wavelength below 280 nm). This leads to disruption of photosynthesis in plants, uncontrolled ecosystem changes, and growth in skin cancer and cataract incidence. There is also danger of catastrophic ozone depletion over the Arctic, since an ozone hole was discovered comparatively recently above Svalbard. In 1985, the international Vienna Convention for the Protection of the Ozone Layer was concluded, and in 1987 the Montreal Protocol developing it was signed. Under these agreements, developed countries stopped producing and selling ozone-depleting chlorofluorocarbons, while developing countries were to do so by 2010. International studies conducted in 1998 demonstrated the effectiveness of the Montreal Protocol. The total amount of ozone-depleting compounds in the troposphere (the lower atmospheric layer) reached its maximum in 1994 and then began to decline. Without measures under the Protocol, ozone depletion would have been much stronger. Although emissions of ozone-depleting substances have declined, the effects of chemicals already released into the atmosphere persist, meaning ozone-layer depletion will continue to be recorded for a long time. Ozone-layer destruction is also promoted by launches of ballistic and space rockets and even by aviation use. During the Yugoslav war, NATO aviation carried out 400-500 sorties daily. The total power of munitions used exceeded by several times the power of the atomic bomb detonated over Hiroshima. Aviation activity caused numerous fires, including at oil-refining and chemical plants. Aircraft emissions, products of explosive destruction, and fires generate compounds capable of destroying the ozone layer. In 1999, compared to 1998, ozone content over Kosovo decreased by 8-10%. In autumn 2005, the US National Oceanic and Atmospheric Administration reported that ozone-layer deterioration had stopped worsening. Although the situation remains difficult, there is hope for improvement over time. It is believed that ozone-layer recovery should occur by 2050, provided all protective measures are strictly implemented. The success of the Montreal Protocol is an important precedent for successful international environmental action. However, it is too early to relax: many factors can still aggravate the situation.
6.09. Global Warming
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction Chapter 6. Human Ecology and Conservation
6.11. Acid Rain