South Pole, ozone hole

Figure 8.3 This is an October 1,1998, NASA satellite image of the ozone hole over the South Pole. The hole was alarmingly large, most likely due to an overabundance of CFCs in the atmosphere that break apart the oxygen molecules of the ozone layer.

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 history of ozone depletion took a dramatic turn in 1985 when J. C. Farman at the BAS Halley Bay station announced that ozone levels over the Antarctic had decreased by more than 40 percent between 1977 and 1984. Farman explained that ozone levels had fallen so low that one could say that a "hole had formed in the ozone layer above the South Pole. In 1984, that "hole covered an area of more than 15 million square miles (40 million square kilometers), equal to the size of the continental United States. Clearly, ozone depletion was not a long-term problem about which scientists could debate for the next century or so. It was an issue that demanded quick attention and action. 

Figure 12.17 shows the ozone profiles over the U.S. Amundsen-Scott Station at the South Pole in 1993 on August 23 prior to formation of the ozone hole and on October 12 after the ozone hole had developed. The total column ozone decreased from 276 DU on August 23 to only 91 DU on October 12, and, in addition, there was essentially no ozone in the region from 14 to 19 km (Hofmann et al., 1994a). During the same period at the McMurdo Station in Antarctica, the total column ozone decreased from 275 to 130 DU (B. J. Johnson et al., 1995). While similar profiles have been observed since the discovery of the ozone hole, these data show some of the most extensive ozone destruction ever observed, although 1994 and 1995 showed almost as much 03... 

FIGURE 12.17 Vertical O, profile before (August 23) and after (October 12) development of the ozone hole at the U.S. Amundsen-Scott Station, South Pole, in 1993 (adapted from Hofmann et al., 1994a). 

Figure 1-1 An ozone hole forms each year in the stratosphere over the South Pole at the beginning of spring in October. The graph compares ozone pressure in August, when there is no hole, with the pressure in October, when the hole is deepest. Less severe ozone loss is observed at the North Pole. [Data from National Oceanic and Atmospheric Administration.]...

Does the ozone pollution from automobiles help shrink the ozone hole over the South Pole Defend your answer. 

In the winter of 1984, massive losses of stratospheric ozone were detected in Antarctica over the South Pole (Halley Bay). This ozone depletion is known as the ozone hole. We know now that it also forms over the Arctic, although not as dramatically as in the Antarctic. Stratospheric ozone protects life on the surface of the Earth by screening harmful UV radiation coming from the sun through a photodissociation mechanism (see Chapter 4). 

O3 destruction is most severe in the region of the South Pole, where a large ozone hole is visible with satellite imaging. 

The amount of ozone in the atmosphere is frequently indicated by the height hos of a vertical column of gaseous ozone under standard conditions (tn = 0 °C, pa = 1.01325 bar). This quantity varies seasonally and with latitude it has an average value of around 2.5 mm at the equator, 3.5mm at medium latitudes and up to 4.5 mm at the poles. The amount of ozone has fallen over several years as a result of the discharge of CFCs. At the beginning of spring a reduction up to 20 % of the average value occurs over northern Europe. The hole in the ozone layer over the south pole, which appears in October, leads to a reduction at times of up to 75 %. 

Each spring since 1979, researchers have observed a thinning of the ozone layer over Antarctica. Each spring (autumn in the Northern Hemisphere) beginning in 1983, satellite images have shown a hole in the ozone layer over the South Pole. During August and September 1987, a NASA research team flew a plane equipped with sophisticated analytical instruments into the ozone hole 25 times. Their measurements demonstrated that as the concentration of the chlorine oxide radicals, Cl—O increased, the concentration of ozone decreased. 

While not a true hole in the sense that some column ozone remains even in the most extreme depletions observed in the mid 1990s (when October ozone minima were near 100 Dobson Units over the South Pole, or depletion of about two-thirds of the historical levels, see Hofmann et al, 1997), the descriptor captures the fact that the peak depletion is sharply limited to Antarctic latitudes. Dobson (1968 and references therein) noted that there is less ozone naturally present over Antarctica than over the Arctic in winter and much of the spring, but this climatological difference between the natural ozone levels over the poles of the two hemispheres should not be confused with the abrupt decline that began near the mid-1970s as depicted in Figure 6.9. Newman (1994) discusses these and other historical measurements of total ozone and shows that the Antarctic ozone hole began only in the last few decades. 

Plate 9. Interannual variability in the Antarctic ozone hole. The figures compare the ozone column abundance observed on September 24 in 2001 and in 2002. In 2001 as in most previous years of the last 2 decades, the hole was centered approximately over the South Pole with low ozone values over the Antarctic continent. In 2002, a strong wave-2 planetary wave disturbed the polar vortex and produced a very peculiar distribution of the ozone column. The warming associated with this event led to limited ozone depletion and a disappearance of the ozone hole at the end of September. From NASA. 

In recent years the amount of O3 in the stratosphere over the South Pole has decreased periodically, resulting in an ozone hole in the atmosphere. The decrease is most pronounced during the summer months of the Southern Hemisphere. If the amount of ozone continues to decrease, more UV hght will reach the surface of Earth, probably causing some skin damage and increasing the incidence of cancer. Chlorine atoms react with and destroy ozone ... 

Explain why the ozone hole has occurred over the South Pole even though the molecules that triggered the hole formation were not released at the Pole. 

The ozone hole has developed primarily over the South Pole because ... 

The phrase ozone hole, however, means something different. Interestingly, the loss of ozone in Earth s atmosphere is much larger above the poles than anywhere else, and even in those areas, it mainly occurs in early spring (March-April above the North Pole, September-October above the South Pole). To make matters more complicated, the two poles are quite different as far as ozone goes the largest drop in ozone concentration was about 30 % at the North Pole, whereas at the South Pole, a drop of up to 70 % is not unheard of. So the ozone hole is not an actual hole in a solid shield, it is more like a large decrease in the texture of an already sparsely woven net (Fig. 1.7). 

This chain process is so destructive that it has created a huge hole above Antarctica and the South Pole, estimated to have a radius of 1,000 km or more. Figure 10.2 shows schematically the ozone hole generation. The CFC (1) rises to the stratosphere, and its C—Cl bond is broken by sunlight, releasing atomic chlorine (2), which destroys the ozone layer and creates a hole (3). Through this hole, intense UV radiation reaches the Earth s surface and leads to dire consequences. 

Surface ozone measurements at the South pole at 2835 m amsl. show a significant decrease of 0.70 0.2% per year in the period of 1975 to 1995. This was attributed to the effect of the ozone hole, which leads to the deereasing supply of ozone from the stratosphere. 

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. 

FIGURE 3-16 The Antarctic ozone hole. The purple and pink colored section in the middle shows the depletion of ozone over the Earth s South Pole. This image is from September 2007. 

This computer image shows the total quantity of ozone over the region near the South Pole, with various colors corresponding to Dobson units (equivalent to the thickness, in units of 10 mm, of total ozone in the atmosphere,assuming it to be compressed to 1 atm at 0°Q.The ozone hole is shown in dark blue,equal to 200 to 225 Dobson units. In September 2002,the ozone hole split into two parts. Data were obtained by theTotal Ozone Mapping Spectrometer (TOMS) aboard the Earth Probe satellite. 

The situation is not as severe in the warmer Arctic region, where the vortex does not persist quite as long. Studies have shown that ozone levels in this region have declined between 4 and 8 percent in the past decade. Volcanic eruptions, such as that of Mount Pinatubo in the Philippines in 1991, inject large quantities of dust-sized particles and sulfuric acid aerosols into the atmosphere. These particles can perform the same catalytic function as the ice crystals at the South Pole. As a result, the Arctic hole is expected to grow larger for several years following an eruption. 

Active chlorine originally from chlorofluorocarbons (CFCs) is sequestered in stratospheric clouds during the dark winter above the South Pole and then released during the Antarctic spring (September and October), destroying protective stratospheric ozone and resulting in the Antarctic ozone hole. 

---