Antarctica, ozone hole over

The discovery of ozone holes over Antarctica in the mid-1980s was strong observational evidence to support the Rowland and Molina hypothesis. The atmosphere over the south pole is complex because of the long periods of total darkness and sunlight and the presence of a polar vortex and polar stratospheric clouds. However, researchers have found evidence to support the role of CIO in the rapid depletion of stratospheric ozone over the south pole. Figure 11-3 shows the profile of ozone and CIO measured at an altitude of 18 km on an aircraft flight from southern Chile toward the south pole on September 21, 1987. One month earlier the ozone levels were fairly uniform around 2 ppm (vol). 

The development of the ozone hole over Antarctica is accelerated by heterogeneous catalysis on microciystals of ice. These microcrystals form in abundance in the Antarctic spring, which is when the ozone hole appears. Ice microciystals are less common in the Arctic atmosphere, so ozone depletion has not been as extensive in the Northern Hemisphere. 

An ozone hole over Antarctica was discovered with especially low concentrations of ozone above that continent in their spring (Northern Hemisphere s fall). This was linked to CFCs. 

The process responsible for the "ozone hole over Antarctica is thought to be similar, though it may be heterogeneous, taking place on ice particles.58... 

FIGURE 9.18 A false- color satellite image of the ozone hole over Antarctica on September 26, 2002. The lowest ozone concentrations are represented by the black and violet regions, where ozone levels are up to 50% lower than normal. 

The ozone hole over Antarctica results from the storage of chlorine-containing molecules on the surfaces of polar stratospheric clouds during the Antarctic winter followed by sudden photolysis and release in the spring. 

James Farman s report of the ozone hole over Antarctica in 1981 was the turning point. The major producers of CFCs (companies such as Dow and DuPont de Nemours), a 9 billion business with annual growth rates of 10% (Thomas 2000) then espoused the worldwide concern. That would finally result in the Montreal Protocol in 1987, banning CFCs, stopping their production, and promoting substitution by HCFCs. 

O Reading Check Explain what triggers the formation of the ozone hole over Antarctica. 

Figure 1.18 The ozone hole over Antarctica reached its maximum level of thinning in September 2005. The color-key below shows what the colors represent in this colorized satellite image. 

Figure 1.18 shows the ozone hole over Antarctica in September 2005. The ozone thinning over Antarctica reached its maximum for the year during this month. If you compare the color-coded key to the satellite image, you can see that the ozone level is between 110 and 200 DU. Notice the area surrounding the ozone hole. Much of this area has ozone levels around 300 DU, which is considered normal. 

A photo showing the ozone "hole" over Antarctica. 

Although the overall process is certainly more complicated, these simplified schemes provide an understanding of the role of Cl atoms in triggering the ozone depletion that leads to the seasonal ozone hole over Antarctica. A single Cl atom is thought to be capable of destroying 100,000 ozone molecules before it is rendered unreactive by some other chemical process. Collected data (Figure 7.6) also show that there is an anticorrelation between the concentration of CIO and the concentration of ozone in the stratosphere. 

We now know that the annual appearance of the ozone hole over Antarctica is caused by the circulation and low temperature of the stratosphere during the southern winter. The CFCs and other anthropogenic... 

Fig. 2.7 The ozone hole over Antarctica in September of 2005 covered an area of more than 24 million square kUometers which is approximately equal to the area of North America. The ozone hole has been forming in the stratosphere over Antarctica since about 1970 as a result of the release of anthropogenic CFC gases into the atmosphere. Computer models now predict that the size of the ozone hole will begin to decline in 2018 and will stop forming altogether in 2068. This is good news because the ozone of the stratosphere absorbs ultraviolet radiation which can cause skin cancer and eye damage in humans and is harmM to marine organisms. The ozone content of the stratosphere over Antarctica has declined annually by about 70% below normal during September and October whereas the decline over the USA has only been between 3% and 6% (Cook-Andersen 2006 Photo courtesy of NASA)...

Although both the area and the depth of the ozone hole over Antarctica have varied annually, the size of the hole has not decreased appreciably even after the manufacture and release of the ozone-destroying gases were prohibited in 1987 by the Montreal Protokol. However, the computer models predict that the area and depth of the ozone hole will begin to decline in 2018 and that it will disappear by the end of the present century. If that happens, we will have successfully reversed the effects of this case of anthropogenic contamination of the atino-sphere (Morell 2007 Stonehouse 2002 Faure 1998 Holland and Petersen 1995 Graedel and Crutzen 1993 Stolarski 1988 Molina and Rowland 1974). 

A NASA satellite showed that in 2009 the ozone hole over Antarctica had a maximum surface area of 24.1 million km. The largest ozone hole on record occurred in 2006 and had a surface area of 29.6 million km. Calculate the difference in diameter (in meters) between the ozone hole in 2009 and in 2006. 

A The ozone hole over Antarctica on September 24, 2009. The dark blue and purple areas over the South Pole represent very depressed ozone concentrations. 

The consequences of releasing these substances into the atmosphere were not recognised for some time. Their effect, which is now recognised, is to create partial holes in the ozone layer and in some extreme cases it has disappeared completely. The most famous ozone holes are over Antarctica but there are signs that northern Europe also has an ozone hole over it. 

Research has shown that heterogeneous catalysis is most likely responsible for the annual formation of an ozone hole over Antarctica. After the discovery of the Antarctic ozone hole in 1985, scientists wondered why there was such a dramatic drop in ozone over Antarctica but not over the rest of the planet. After aU, the chlorine from chlorofluorocar-bons that catalyzes ozone destruction is evenly distributed throughout the entire atmosphere. 

During the mid-1980s, each September scientists began to observe a decrease in ozone in the stratosphere over Antarctica. These observations are referred to as "ozone holes." In order to understand ozone holes, one needs to know how and why ozone is present in the earth s stratosphere. 

J. C. Farman discovered the ozone hole (substantial seasonal depletion of ozone) over Halley Bay, Antarctica. 

Mario Molina and Sherwood Rowland used Crutzen s work and other data in 1974 to build a model of the stratosphere that explained how chlorofluorocarbons could threaten the ozone layer. In 1985, ozone levels over Antarctica were indeed found to be decreasing and had dropped to the lowest ever observed by the year 2000, the hole had reached Chile. These losses are now known to be global in extent and it has been postulated that they may be contributing to global warming in the Southern Hemisphere. 

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