The term "ozone hole" refers to a large and rapid decrease in the concentration of ozone molecules in the ozone layer. "When the concentration of ozone over any area falls below 220 DU, it is called ozone hole".
The Antarctic "Ozone Hole" occurs during the southern spring between September and November each year. The British Antarctic survey team first reported the hole in May 1985. The team found that for the period between September and mid November, ozone concentration over Halley Bay, Antarctic, had declined by 40% from levels during the 1960s. Severe depletion has been occurring since late 1970s.
The problem is worst in this part of the globe due to extremely cold atmosphere and the presence of polar stratospheric clouds. The land under the ozone depleted atmosphere increased steadily to more than 20 million sq km in the early 1990s and in the Antarctic spring of 1998, the area of the ozone hole exceeded 26 million sq km and also covered some populated areas of the southern hemisphere. The total ozone dropped to about 97 DU on 1 October, 1998.
The Antarctic ozone hole grew to 28.4 million sq. km in 2000. In the year 2002, a peculiar effect was seen, the ozone hole split into two but the total coverage was only 15 million sq. km. In the year 2005, the size of ozone hole again increased to 27.0 million sq. km. The ozone hole further grew to an extraordinary size, 29.3 million sq. km in 2006. The size of ozone hole slightly started declining and in 2008 became equivalent to the size of North America and NOAA reported that ozone hole reached to 26.5 million sq. km. in September, 2008. It was also observed that the total column of ozone dropped to its lowest count of 100 DU in September, 2008. The size of Antarctic ozone hole in September, 2009, September, 2010, September, 2011, September, 2012, September, 2013 and September, 2014 were reported to be 24 million sq. km., 22.2 million sq. km., 25 million sq. km., 18.5 million sq. km., 21 million sq. km. and 24.3 million sq. km. respectively.
The latest false-color view of total ozone over the Antarctic pole. The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone.
This indicates that the Montreal Protocol is working effectively and there is a gradual recovery of ozone layer.
The decline of ozone layer over North Pole has also been reported. The effect has been ascribed to solar flares and record frigid temperatures working with manmade chemicals.
In addition, research has shown that ozone depletion occurs over the latitudes that include North America, Europe, Asia, and much of Africa, Australia and South America. Thus, ozone depletion is a global issue and not just a problem at the South Pole. It was also reported that some ozone depletion also occurs in the Arctic during the Northern Hemisphere spring (March-May). Wintertime temperatures in the Arctic stratosphere are not persistently low for many weeks and these results in less ozone depletion.
Recent observations and several studies have shown that the size of annual ozone hole has stabilized and the level of ODSs has decreased by 4 percent since 2001. But chlorine and bromine compounds have long atmospheric life. Recovery of stratospheric ozone is not likely to be noticeable until 2020 or little later.
As explained earlier, ozone acts as a shield to protect the Earth's surface by absorbing harmful UV-B and UV-C radiation. If this ozone is depleted, then more UV rays will reach the earth surface. Exposure to higher doses of UVB radiations will have effects on human health and impact on flora and fauna of terrestrial as well as aquatic eco-systems.
Human health effects:
Adverse impact on agriculture, forestry and natural ecosystems:
Damage to marine life:
Materials:
Last Modified : 5/9/2024
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