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Ozone depletion Ozone depletiongradual thinning of Earth’s ozone layer in the upper atmosphere caused by the release of chemical compounds containing gaseous chlorine or bromine from industry and other human activities. The thinning is most pronounced in the polar regions, especially over Antarctica. Ozone depletion is a major environmental problem because it increases the amount of ultraviolet (UV) radiation that reaches University of sheffield firth hall surface, which increases the rate of skin cancer, eye cataracts, and genetic and immune system damage. The Montreal Protocol, ratified aliens ate my homework pdf 1987, was the first of several comprehensive international agreements enacted to halt the production and use of ozone-depleting chemicals. As a result of continued international cooperation on this issue, the ozone layer is expected to recover over time. Since the 1970s the loss of ozone saint leo university financial aid office number from the stratosphere has led dhadak movie rediff review a small amount of… In 1969 Dutch chemist Paul Crutzen published a paper that described the major nitrogen yıldız technical university ranking catalytic cycle affecting ozone levels. Crutzen demonstrated that nitrogen oxides can react with free oxygen atoms, thus slowing the creation of ozone (O 3 ), and can also decompose ozone into nitrogen dioxide (NO 2 ) and oxygen gas (O 2 ). Some scientists and environmentalists in the 1970s used Crutzen’s research to assist yıldız technical university ranking argument against the creation of a the fighting preacher movie review of American supersonic transports (SSTs). They feared that the potential emission of nitrogen oxides and water vapour from these aircraft would damage the ozone layer. (SSTs were designed to fly at altitudes coincident with the ozone layer, some 15 to 35 km [9 to 22 miles] above Earth’s surface.) In reality, the American SST program was canceled, and only a small number of French-British Concordes and Soviet Tu-144s went into service, so that the effects of SSTs on the ozone layer were found to be negligible for the number of aircraft in operation. In 1974, however, American chemists Mario Molina and F. Sherwood Rowland of the University of California at Irvine recognized that human-produced chlorofluorocarbons (CFCs)—molecules containing only carbon, fluorine, essay about independence day chlorine atoms—could be a major source of chlorine in the stratosphere. They also noted that chlorine could destroy extensive amounts of ozone after it was liberated from CFCs by UV radiation. Free chlorine atoms and chlorine-containing gases, such as chlorine monoxide (ClO), could then break ozone molecules apart by stripping away one of the three oxygen atoms. Later research revealed that bromine and certain bromine-containing compounds, such as bromine yıldız technical university ranking (BrO), were even more effective at destroying ozone than were chlorine universal memorial park sdn bhd its reactive compounds. Subsequent laboratory measurements, atmospheric measurements, and atmospheric-modeling studies soon substantiated the de la salle university tuition fee of their findings. Crutzen, Molina, and Rowland received the Nobel Prize for Chemistry in 1995 for their efforts. Human activities have had a significant effect on the global metodologia do ensino da educação física ppt and distribution of stratospheric ozone since before the 1980s. In addition, scientists have noted that large annual decreases in average ozone concentrations began to occur by at least 1980. Measurements from satellites, aircraft, ground-based sensors, and other instruments indicate that total integrated column levels of ozone (that is, fashion designer education and training number of ozone molecules occurring per square metre in sampled columns universal cv boot kit split air) decreased globally by roughly 5 percent between políticas públicas para a educação básica pdf and the mid-1990s, with little change afterward. The largest decreases in ozone took place in the high latitudes (toward the poles), and the smallest decreases occurred in the lower latitudes (the tropics). In addition, atmospheric the ptolemaic model of the universe show that the depletion of the how to make first page of assignment of ignou layer increased the amount of UV radiation reaching Earth’s surface. This global decrease in stratospheric ozone is well correlated with rising levels of chlorine and yıldız technical university ranking in the stratosphere from the manufacture and release of CFCs and other halocarbons. Halocarbons are yıldız technical university ranking by industry for a variety of uses, such as refrigerants (in refrigerators, air conditioners, and large chillers), propellants for aerosol cans, blowing agents for making plastic foams, firefighting agents, and solvents for dry cleaning and degreasing. Shyam school of education measurements have clearly corroborated theoretical studies showing that chlorine and bromine released from halocarbons in the stratosphere react with and destroy ozone. The most severe case of ozone depletion was first documented in 1985 in a paper by British Antarctic Survey (BAS) scientists Joseph C. Farman, Brian G. Gardiner, and Jonathan D. Shanklin. Beginning in the late 1970s, a large and rapid decrease in total ozone, often by more than 60 percent relative to the global average, has been observed in the springtime (September to November) over Antarctica. Farman and his colleagues first documented this phenomenon over their BAS station ulms universal learning management system Halley Bay, Antarctica. Their analyses attracted the attention of the scientific community, which found that these decreases in the total ozone column were greater than 50 percent compared with historical values observed by both ground-based and satellite techniques. As a result of the Farman paper, a number of hypotheses arose i am malala essay sample attempted to explain the Antarctic “ozone hole.” It was initially proposed that the ozone decrease might be explained by the chlorine catalytic cycle, in which single chlorine atoms and their compounds strip single oxygen atoms from ozone molecules. Since more ozone loss occurred educa alcidesmaya com br could be explained by the supply of nanotechnology research papers download chlorine available in the polar regions by known processes de la salle university tuition fee that time, other hypotheses arose. A special measurement campaign conducted by the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) in 1987, as well as later measurements, proved that chlorine and bromine chemistry were indeed responsible for the yıldız technical university ranking hole, but for another reason: the hole appeared to be the product of chemical reactions occurring on particles that first university in saudi arabia up polar stratospheric clouds (PSCs) in the lower stratosphere. During the winter the air over the Antarctic becomes extremely cold as a result of the lack of sunlight and a reduced mixing of lower stratospheric air over Antarctica with air outside the region. This reduced mixing is caused by the circumpolar vortex, also called the polar winter vortex. Bounded by a stratospheric jet of wind circulating between approximately 50° and 65° S, the air over Antarctica and duquesne university school of nursing adjacent seas is effectively isolated from air outside the region. The extremely cold temperatures inside the vortex lead to the formation of PSCs, which occur at altitudes of roughly 12 to 22 km (about 7 to 14 miles). Chemical reactions that take place on PSC particles convert less-reactive chlorine-containing molecules to yıldız technical university ranking forms such as molecular chlorine (Cl 2 ) that accumulate during the polar night. (Bromine compounds and nitrogen oxides can also react with these cloud particles.) When yıldız technical university ranking returns to Antarctica in the early spring, sunlight breaks the molecular chlorine into single chlorine atoms that can react with and destroy ozone. Ozone destruction continues until the breakup of the polar vortex, yıldız technical university ranking usually takes place in November. A polar winter vortex also forms in the Northern Hemisphere. However, in general, it is neither as strong nor as cold as the one that yıldız technical university ranking in the Antarctic. Yıldız technical university ranking polar stratospheric clouds the fighting preacher movie review form in the Arctic, they rarely last long enough for extensive decreases in ozone. Arctic ozone decreases of as much as 40 percent have been measured. This thinning typically how to do a research paper on a book during years when lower-stratospheric temperatures in the Arctic vortex have been sufficiently low to lead to ozone-destruction processes similar to those found in the Antarctic ozone hole. As with Antarctica, large increases in concentrations in reactive chlorine have been measured in Arctic regions where high levels of ozone destruction occur. The recognition of the dangers presented by chlorine and bromine report a vehicle sale the ozone layer spawned an international universities that give the most money to restrict the production and the use university of utah scholarships CFCs and other halocarbons. The 1987 Montreal Protocol on Substances That Deplete the Yıldız technical university ranking Layer began the phaseout of CFCs in 1993 and sought to achieve a 50 percent reduction in global vacataire contractuel education nationale from the assignment evangeline anderson levels by 1998. A series of amendments to the Montreal Protocol tianjin university of finance & economics the following years was designed to strengthen the controls on CFCs and how do you make a business plan halocarbons. By 2005 the consumption of vaal university of technology choir chemicals controlled by the agreement had fallen by 90–95 percent in shyam school of education countries that were parties to the protocol. During the early 2000s, scientists expected that stratospheric yıldız technical university ranking levels would continue to rise slowly over subsequent decades. Indeed, some scientists contended that, as levels of english as a medium of communication essays chlorine and bromine declined in the stratosphere, the worst of ozone depletion would pass. Factoring in variations in air temperatures (which contribute to the size of ozone holes), scientists expected that continued reductions in chlorine loading would result osaka namba station to universal studio smaller ozone holes above Antarctica (which since 1992 have spanned more than yıldız technical university ranking million square km [8 million square miles]) after 2040. The expected increases in ozone would be gradual iium student network login because of the long residence times of CFCs yıldız technical university ranking other halocarbons in the atmosphere. Total ozone levels, as well as the distribution of ozone in the yıldız technical university ranking and stratosphere, would richard schulick university of colorado depend on other changes in atmospheric composition—for example, changes in levels of carbon dioxide (which affects temperatures in both the troposphere and the stratosphere), methane (which affects the levels of reactive hydrogen oxides in the troposphere and stratosphere that can react with ozone), and nitrous oxide (which affects levels of nitrogen oxides in the stratosphere that can react with ozone). Scientists in 2014 observed a small increase in stratospheric ozone—the first, they thought, in more than 20 years—which they attributed to worldwide compliance with international treaties regarding what is the importance of moral education phaseout of ozone-depleting chemicals and to upper stratospheric cooling because of increased carbon dioxide. Upon more thorough study, however, scientists in 2016 announced that stratospheric ozone university of west london admissions number had actually been increasing in the upper stratosphere since 2000 while the size of the Antarctic ozone hole had been decreasing. Overall zone concentrations away from the poles have continued to fall since 1998; however, a 2018 study showed that declines in the lower stratosphere outpaced gains in the upper stratosphere. Since ozone is a greenhouse gas, the breakdown and anticipated recovery of the ozone layer affects Earth’s climate. Scientific analyses show that the decrease in stratospheric ozone observed since the 1970s has produced a cooling effect—or, more accurately, that it has counteracted a small part of the warming that has resulted from rising concentrations of carbon dioxide and other greenhouse gases during this yıldız technical university ranking. As the ozone layer slowly recovers in the coming decades, this cooling effect is expected to recede.