The Earth’s atmosphere is made up of different layers. The layer closest to the surface is called the troposphere which extends from the Earth’s surface up to about 10 km. The ozone layer is located above the troposphere in the stratosphere (10 km to about 50 km high). Stratospheric ozone is Earth’s natural protection for all life forms, shielding our planet from harmful ultraviolet-B (UV-B) radiation. UV-B radiation is harmful to humans, animals, and plant life. The ozone layer is being destroyed by certain industrial chemicals including ozone depleting refrigerants, halons, and methyl bromide, a deadly pesticide used on crops.

Ozone depletion damage gets much worse, when the stratosphere is very cold. This has been the case the past two years, causing extensive ozone depletion. This past winter, ozone depletion reached the most severe levels ever recorded over the Northern Hemisphere. Western United States ozone levels also continue to drop 3-4 % per decade. Even, if all of our efforts to stop harmful emissions are successful, the ozone layer is not expected to begin recovery until around 2020 at the earliest.

Ozone depletion occurs in many places in the Earth’s ozone layer, most severely in the Polar Regions. NOAA scientists have travelled to Antarctica to study the ozone hole that has been occurring there since the late 1970. In 1986, soon after the reported discovery of the ozone hole, Aeronomy Lab (now ESRL) scientist Dr Susan Solomon led a team of 16 scientists, reached to the conclusion that human produced trace gases containing chlorine and bromine were causing the ozone hole.

This unique record from the South Pole station clearly shows the annual development of the springtime Antarctic ozone hole over the past two decades. Ozone depletion at the South Pole can also be viewed from another perspective through the images created from data collected by the NASA TOMS satellite, and the NOAA SBUV-2 instruments aboard NOAA satellites. Continued surveillance is necessary in order to verify the expected recovery of the ozone layer.

Recent Phenomenon

A huge hole, that appeared in the Earth’s protective ozone layer above the Arctic in 2011, was the largest recorded in the Northern Hemisphere, though the sudden appearance of the hole was not due to man made causes, scientists said in a report on Monday. For some years, the holes have been so large that they covered the entire continent and stretched to parts of South America.

During extreme events, up to 70% of the ozone layer can be destroyed before it recovers months later. The hole above the Arctic was always much smaller – until March, 2011, when a combination of powerful wind patterns and intense cold temperatures high up in the atmosphere created the right conditions for already present, ozone-eating chlorine chemicals to damage the layer.

The findings show that the hole had opened over Northern Russia, parts of Greenland, and Norway, meaning people in these areas were likely to have been exposed to high levels of UV radiation.

“The chemical ozone destruction over the Arctic in early 2011 was, for the first time in the observational record, comparable to that in the Antarctic ozone hole,” say the scientists, led by Gloria Manney of the Jet Propulsion Laboratory in Pasadena, California.

The scientists say manmade chemicals such as chlorofluorocarbons(CFCs) destroy ozone in the stratosphere, after sunlight breaks up the complex chemicals into simpler forms that react with ozone. While some of the chemicals are covered by a UN treaty that aims to stop their use, it will be  decades before, they are fully phased out of production.

Normally, atmospheric conditions high above the Arctic do not trigger a large scale plunge in ozone levels. But, during the 2010/11 winter, a high-altitude wind pattern called the polar vortex was unusually strong, leading to very cold conditions in the stratosphere that also lasted for several months. This created the right conditions for the ozone-destroying forms of chlorine to slash ozone levels over a long period.

The United Nation’s Environment Programme initiated work in 1981, aimed at the elaboration of a global framework for the protection of the ozone layer. After several years of negotiations, the Vienna Convention for the protection of the Ozone Layer was adopted in March 1985. The convention provides for international co-operation in research, monitoring, and exchange of data. This was the first time, that the international community had recognized a need for action on an environmental problem before actual damages were recorded. Agreement was not reached at that time, however, on concrete measures to control ozone depleting chemicals. Instead, a process was launched to improve understanding of the nature and impacts of ozone depiction and to narrow differences in various countries approaches to the problem. This process included: two UNEP workshops, in Rome in May 1986, and in Leesburg, Virginia in September 1986, on key economic and conceptual issues related to the control of ozone depleting chemicals; an International Conference in June 1986, cosponsored by the US Government and the UNEP, on the effects of ozone depletion and climate change; and detailed assessments by the international scientific community of atmospheric science and the effects of ozone depletion. A highlight was the publication of a document on atmospheric ozone, prepared by 150 scientists co-ordinate by Dr Robert Watson of NASA, under the sponsorship of NASA, the UNEP, the World Meteorological Organization, the European Commission, NOAA (National Oceanic   and   Atmospheric   Administration),   FAA   (Federal   Aviation Administration)  and  the  German  Federal  Ministry  for  Research and Technology.

The Latest Report: Depletion Stabilized

“The depletion of ozone layer (a thin shield that envelopes the Earth and filters and screens all harmful ultraviolet rays) has now stabilized, according to experts. In the path of recovery, it will take around fifty years for the ozone layer to go back to the stage it was in 1970’s,” said Atul Bagai, Senior Regional Co-coordinator, United Nations Environment Programme (UNEP).

Bagai was speaking at a workshop on ‘media towards environment’ organized by the department of Journalism, Marathwada Mitra Mandal’s College of Commerce and TERRE Policy Centre, on Thursday.

He said the Chlorofluorocarbons (CFCs) and other halogenated Ozone Depleting Substances (ODSs), mainly responsible for manmade chemical ozone depletion, were phased out in 2010. CFC was used in air conditioning, refrigeration, solvents, aerosol sprays, among others. The production and its use have stopped.

Bagai pointed out, that at present we can prevent further deterioration of the ozone layer. But, the already released CFC is causing the damage. “And now, the international committee wants to phase out Hydro fluorocarbon (HCFC) by 2030, that cause ozone destruction and are potent greenhouse gases. Foam blowing is one on the main uses of HCFCs, other-than refrigeration, chillers, among others. The air conditioning market has grown 20-25% annually in the last ten years, and so the use of HFC has also gone up,” he said.

On the occasion, Rajendra Shende, Head of the Ozon Action Programme, UNEP, said the Montreal Protocol has been effective at protecting the ozone layer.