Ozone Depletion
An image of total ozone column profile around the North Pole on March 30, 2011 developed by Finnish Meteorological Institute using satellite and ground based data is seen in this April 5, 2011 handout. Record loss of the ozone, the atmosphere layer that shields life from the sun's harmful rays, has been observed over the Arctic in recent months. the World Meteorological Organization said on Tuesday. Satellite measurement of total ozone from OMI (Ozone Monitoring Instrument) shows a region of low ozone (blue region) above the Arctic regions. As of late March the ozone poor region is shifted away from the pole and covers Greenland and Scandinavia. Reuters/World Meteorological Organization/Handout

In 1989, the United Nations enforced a treaty to regulate the use and production of chemicals that cause ozone depletion. Since then, the Montreal Protocol has had six amendments to include scientific update on substances that damage Earth’s atmosphere. A recent report by scientists from the School of Earth and Environment at the University of Leeds states that some chemicals not included in the treaty have been damaging the ozone layer. These very short-lived substances (VSLS) are increasing in the atmosphere.

VSLS production is not regulated by the Montreal Protocol because these substances had negligible effect on the ozone layer in the past decades. However, concentrations have been increasing rapidly and scientists found that their abundance in the lower stratosphere greatly contributes to ozone loss and climate change. Unlike longer-lived chemicals such as chlorofluorocarbons (CFCs) that damage the uppermost layer of the atmosphere, VSLS tend to cause ozone depletion at the lower layers because they break down easily.

The scientists analysed concentrations of VSLS in the atmosphere for the past 20 years using data prepared by the National Oceanic and Atmospheric Administration (NOAA). The team found that dichloromethane, a short-lived substance produced for industrial use, has higher levels. VSLS are emitted naturally or man-made, so the scientists had to distinguish the sources and the effects of each in the atmosphere. Short-term substances produced by natural sources like seaweed are responsible for 90 percent of ozone damage in the lower stratosphere. VSLS emitted by human activities have been increasing significantly and amounts are expected to amplify further.

Martyn Chipperfield, co-author of the study emphasises the importance of continuous monitoring of gases that threaten the recovery of the ozone layer. Controlling fluorocarbon emissions and use of other ozone-depleting substances will be pointless if other chemicals that have not been identified in the UN treaty constantly abound in the atmosphere. Also, although ozone loss brought about by VSLS is not as expansive compared to the damage caused by other gases, the impact on climate change is 4 times greater.

Dichloromethane (DCM) is used in some industrial processes. The reason for noticeable growth in DCM concentrations is not yet verified, but the researchers partially attribute it to its use in manufacturing ozone-friendly chemicals to substitute CFCs. This research was published in the Feb 16 issue of Nature Geoscience.

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