Antarctic ozone hole

Antarctic ozone hole

Recently Antarctic ozone hole was in the news. According to World Meteorological Organization (WMO), Antarctic ozone hole is one of the deepest, largest in the last 40 years, has closed.

 The formation of ozone hole in the Antarctic has been an annual thing and has been recorded for the last 40 years. This year, ozone hole over Antarctic had rapidly grown from mid-August and reach at peak in early October 2020. This time around, expansion of the hole was drive by a strong, stable and a cold polar vortex. which make the temperature of the ozone layer over Antarctica consistently cold. This prevents the mixing of ozone depleted air above Antarctica with ozone rich air from higher latitude.  

 Ozone layer is the common term for the high concentration of ozone that is found in the stratosphere which is a layer of atmosphere between around 10- 50 km altitude. Atmospheric ozone absorbs ultraviolet (UV) radiation from the sun. It absorbs particularly harmful UV B-type rays. 

Ozone hole

About ozone hole

Ozone hole refers to a region in stratosphere where concentration of ozone gas becomes extremely low. These holes are spotted over both the Poles. Ozone depletions at North pole are much smaller in size, because of the warmer temperatures in North Pole than the South Pole.
Ozone depletion is directly related to the formation of Polar vortex in stratosphere. During winter, temperatures in the vortex usually drop drastically below 195 K (-78°C), and polar stratospheric clouds (PSCs) form. Polar stratospheric clouds provide  surface for ozone depleting substances such as chlorine containing CFCs, HCFCs, bromine containing halons etc. to reach stratosphere.

At the poles, OZone depletion substance attach to ice particles in PSCs. And When the sun rise again in the polar spring, the ice particles melt, releasing the ozone-depleting molecules from the ice particle surfaces. Once released, these ozone destroying molecules harm and breaking apart the molecular bonds in UV radiation absorbing ozone. During the Southern Hemisphere spring season (August to October) the ozone hole over the Antarctic increases in size. It reachs at maximum between mid-September and mid-October.

Ozone depletion slow down when temperature in stratosphere start to rise, in late Southern Hemisphere spring. And the polar vortex weakens and breaks down. This is because in warmer temperatures fewer PSCs form and they don’t survive as long, limiting the ozone-depletion process. By the end of December ozone levels return to normal.

Ozone gas is measure as the total amount that is present in a column of overlying atmosphere in Dobson units. One Dobson unit can be thought of as the amount of ozone that would be present if it formed a layer 0.01mm thick at average sea-level pressure and temperature.

What is polar vortex? 

A polar vortex is a low pressure area of wide expanse of spiral cold air in polar regions. It always exists near the poles. It weakens in summer and strengthens in winter. The term “vortex” refers to the counter clockwise flow of air that helps in keeping the colder air near the Poles. A stronger polar vortex tends to enclose in the cold (by bottling up all the cold air at poles), while a weaker one allows cold blaze to visit the mid-latitudes. On occasions, this vortex can become disturbed, mainly in the Northern Hemisphere. It is because of the different arrangement of land and sea in the two hemispheres. In the northern hemisphere, there are many regions of land-sea temperature contrast, which can create atmospheric waves that can disturb the vortex. In the southern hemisphere, there is sea almost everywhere, which is continuous around Antarctica. 

Polar vortex

Effects of ozone depletion on humans and the environment 

Ozone layer depletion causes increased Ultraviolet radiation levels at the Earth’s surface, which is damaging to human health. 

Negative effects include  increases in different types of skin cancers, eye cataracts and immune deficiency disorders. Ultraviolet radiation also affects terrestrial and aquatic ecosystems. It alters the growth, food chains and biochemical cycles. Aquatic life just below water’s surface have particularly adverse affect by high UV levels. UV rays also affect plant growth, and reducing agricultural productivity. 

International Treaties and Cooperation about the Protection of the Stratospheric Ozone Layer

 The Vienna Convention (1985) for the Protection of the Ozone Layer is the precursor to the Montreal Protocol. It is often called a framework convention, because it served as a framework for efforts to protect the ozone layer. 

Montreal Protocol (adopted in 1987) on Substances that Deplete the Ozone Layer regulates production and consumption of nearly 100 ozone depleting substances (ODS). 

The Kigali Amendment (adopted in 2016) to Montreal Protocol extended controls to phase down the production and consumption of hydrofluorocarbons (HFCs) because these substances are powerful greenhouse gases. 

United Nations Environment Programme (UNEP) Ozone Secretariat to implement the Montreal protocol.

International treaties on ozone depletion
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