Ozone hole Arctic

Du Pont, the largest producer of CFCs, called for a total CFC production phaseout. A possible arctic ozone hole was studied. The EPA called for a total ban of CFCs. 

Austin, J., N. Butchart, and K. P. Shine, Possibility of an Arctic Ozone Hole in a Doubled-C02 Climate, Nature, 360, 221-225 (1992). 

A third issue is the estimates of ozone loss associated with the polar vortex. Will the Antarctic ozone hole expand and will the Arctic ozone hole begin Can the loss of ozone be better quantified, and what are the zonal asymmetries in the CIO and BrO fields How much additional ozone is lost when the polar vortex breaks up ... 

Austin J, Butchart N, Shine KP (1992) Possibility of an Arctic ozone hole in a doubled-C02 climate. Nature 360 221-225... 

More recent observations have detected a similar ozone hole in the Artie, but it is smaller and much more variable, largely because the temperatures vary more there. Volcanic activity that injects sulfur dioxide into the atmosphere also has an effect that depends on temperature and on the height of the SOs injection. The SO2 reacts with air to form SO3, which then reacts with water to form sulfuric acid aerosols. These volcanic aerosols, particularly at cold polar temperatures, reduce the nitrogen oxide concentration of the air and activate chlorine species that destroy ozone, as do the polar stratospheric clouds described earlier. Because these aerosols are stable at warmer temperatures ( 200 K) than the natural stratospheric clouds, and because they can exist at lower altitudes, they can have significant effects. Until the level of chlorine is reduced to preindustrial levels, low temperatures and volcanic activity are likely to create Arctic ozone holes each spring as a result of reactions during the winter. 

Thus, the mean temperature of the atmosphere, which is about 20°C at sea level, falls steadily to about —55° at an altitude of 10 km and then rises to almost 0°C at 50 km before dropping steadily again to about —90° at 90 km. Concern was expressed in 1974 that interaction of ozone with man-made chlorofluorocarbons would deplete the equilibrium concentration of ozone with potentially disastrous consequences, and this was dramatically confirmed by the discovery of a seasonally recurring ozone hole above Antarctica in 1985. A less prominent ozone hole was subsequently detected above the Arctic Ocean. The detailed physical and chemical conditions required to generate these large seasonal depletions of ozone are extremely complex but the main features have now been elucidated (see p. 848). Several accounts of various aspects of the emerging story, and of the consequent international governmental actions to... 

Ozone depletion is by no means restricted to the Southern Hemisphere. In the extremely cold winter of 1994-1995, a similar "ozone hole" was found in the Arctic. Beyond that, the concentration of ozone in the atmosphere over parts of Siberia dropped by 40%. 

Events that take place on a grand scale often can be traced to the molecular level. An excellent example is the depletion of the ozone layer in the Earth s stratosphere. The so-called ozone hole was first observed above the Antarctic in the 1980s and is now being observed above both the Arctic and Antarctic poles. The destruction of ozone in the stratosphere is caused primarily by reactions between chlorine atoms and ozone molecules, as depicted in our molecular inset view. 

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. 

Arctic stratosphere due to chemistry that is qualitatively similar to that in the Antarctic, an analogous ozone hole is not formed. The major reason for this difference is the different meteorology and dynamics (Schoeberl et al., 1992 Manney and Zurek, 1993 Man-ney et al., 1996). 

There is already one excellent example of our failure to make such a predictive leap—the Antarctic ozone hole. The reason for the failure to anticipate the rapid loss of ozone in the lower stratosphere was a failure to appreciate the potential role of the subtle photochemistry, in particular, the heterogeneous chemistry. Nor did researchers have a full appreciation for the consequences of the air parcels inside the polar vortices being relatively isolated from midlatitude air. Some of these same issues are important in the Arctic region in wintertime, but researchers lack the predictive capability to determine how ozone will ultimately be affected. 

Figure 2 Ozone hole observed in March above the Arctic in March from 1996 to 2000 by GOME compared to the average TOMS March values for 1979 to 1983. Mean polar vortex position is indicated by the 38PVU isoline at the 47SK potential temperature surface...

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). 

This cycle was proposed by Barrie et al. (1988) for the Arctic. Earlier it had been proposed by Wofsy et al. (1975) for the stratosphere, but shown to be unimportant there. Note that in the troposphere only the BrO self-reaction is of importance, whereas in the stratospheric ozone hole the CIO self-reaction (forming the CI2O2 dimer) dominates O3 destruction. Halogen oxide cross-reactions are... 

Based on measurements of the total column ozone content of the atmosphere from the ground as well as from satellites, a consistent picture of the current loss of stratospheric ozone can be derived. The most recent results are discussed in ref. [3]. Relative to the values in the 1970 s, the ozone loss at the end of the 1990 s is estimated to be about 50% in the Antarctic spring, where the ozone hole appears every year, and about 15% in the Arctic spring. In the mid-latitudes of the Southern hemisphere the loss is about 5% all the year round, while in the Northern hemisphere it is about 6% in winter/spring and about 3% in sum-mer/fall. No significant trend in ozone has been found in the Equatorial regions. In the second half of the 1990 s relatively little change in ozone has been observed in the mid-latitudes of both hemispheres. 

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. 

Halogen Chemistry on PSCs. The cold temperatures that occur in polar winter can lead to formation of clouds within the stratosphere, and there are visual sightings of such Arctic clouds dating back hundreds of years. In the unpopulated Antarctic, the earliest explorers noted unusually colorful high clouds in winter. The term polar stratospheric clouds (or PSCs) was coined by McCormick et al. (1982), who first presented satellite observations of high-altitude clouds in the Antarctic and Arctic stratospheres, but the clouds were considered little more than a scientific curiosity until the ozone hole was discovered. 

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