The Antarctic Ozone Hole

Ozone Hole

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.

Environmental Effects of Ozone Depletion

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:

• Sunburns, premature ageing of the skin.
• UV radiation can damage several parts of the eye, including the lens, cornea, retina and conjunctiva.
• As per World Health Organization (WHO), 2002 report, a 10% decrease in stratospher ic ozone could cause an additional 300,000 non-melanoma and 4500 melanoma skin cancers in the world.
• More cataracts leading to damage to the eye vision resulting in blindness. Cataracts (a clouding of the lens) are the major cause of blindness in the world. Ten percent thinning of the ozone layer could cause 1.6 to 1.75 million more cases of cataracts worldwide every year (WHO, 2002).
• Early findings suggest that exposure to UV radiation results in suppression of the human immune system, which may cause non-melanoma and skin cancer.

Adverse impact on agriculture, forestry and natural ecosystems:

• Several of the world's major crop species are particularly vulnerable to increased UV radiation, resulting in reduced growth, photosynthesis and flower ing. Food production may reduce by about 1% for every 1% increase of UV-B radiation.
• The effect of ozone depletion on the agricultural sector could be significant. Many agricultural crops sensitive to the UV-B radiation of the Sun are rice, wheat, soybean, corn, sweet corn, barley, oats, cowpeas, peas, carrots, cauliflower, tomato, cucumber, broccoli etc.
• A few commercially important trees have been tested for UV-B radiation sensitivity. Results indicate that plant growth, especially in seedlings, is more vulnerable to intense UV radiation.

Damage to marine life:

• Planktons are the first vital step in aquatic food chains. In particular, plankton (tiny organisms on the surface layer of oceans) is threatened by increased UV-B radiation.
• Decreases in plankton could disrupt the fresh and saltwater food chains, and lead to species shift.
• Marine fauna like fish lings, juvenile stages of shrimp and crab have been threatened in recent years by increasing UV-B radiation under the Antarctic region. Loss of biodiversity in oceans, rivers and lakes could impact on aquaculture prospects.

Materials:

• Wood, plastic, rubber, fabrics and many construction materials are degraded by UV-B radiation.

Source : The Montreal Protocol India's Success Story