ozone layer depletion

[Dr. DIPTI MATHUR]

OZONE LAYER DEPLETION

 

What is Ozone Layer?

Ozone Layer is a deep layer in earth’s atmosphere that contains ozone which is a naturally occurring, highly reactive molecule that contains three oxygen atoms. It is constantly being formed and broken down in the high atmosphere, 6.2 to 31 miles (10 to 50 kilometers) above Earth, in the region called the stratosphere. This lower region of stratosphere containing relatively higher concentration of ozone is called Ozonosphere. The average concentration of ozone in the atmosphere is around 0.6 parts per million. The thickness of the ozone layer differs as per season and geography. The highest concentrations of ozone occur at altitudes from 26 to 28 km (16 to 17 miles) in the tropics and from 12 to 20 km (7 to 12 miles) towards the poles.

Why Ozone Layer is necessary?

The ozone layer forms a thick layer in stratosphere surrounding the earth, containing large amount of ozone. The ozone layer was discovered in 1913 by the French phycists Charles Fabry and Henry Buisson. It has a property to block solar radiations of wavelength less than 290 nm from reaching Earth’s surface. Thus, it can absorb about 98% of UV radiations which can produce long term harmful effects on human beings as well as plants and animals.

 

Causes of Ozone Layer Depletion

During the last several decades, human activities have resulted considerable reduction of ozone layer in the atmosphere. It occurs when destruction of the stratospheric ozone is more than the production of the molecule. It was first observed in early1970s and was found to be more prominent in Polar Regions.

Ozone hole refers to the regions of severely reduced ozone layers. The two regions where the ozone layer has depleted is the middle latitude and atmospheric regions over Antarctica

Natural causes of depletion of ozone layer

Ozone layer has been found to be affected by certain natural phenomenon such as sun spots and stratospheric winds. But it causes only 1-2% depletion and that is also temporarily.

Manmade causes of depletion of ozone layer

The main cause of depletion of ozone layer is CFCs (Chlorofluorocarbons),halons(methyl chloroform),carbon tetrachloride, methyl bromide, etc. These are categorized as ozone depleting substance (ODS). CFCs are used in freezers, air cooling component, dry-cleaning, etc. methyl chloroform in adhesives and chemical processing, carbon tetrachloride in fire extinguishers.

These substances remain in the atmosphere for quite a long time and is not recycled in the form of rain on the earth and thus transported into the stratosphere.

 The emission of ODS account for roughly 90% of total depletion of ozone layer . These gases are carried to the stratosphere where UV radiations from the sun break them to release chlorine (from CFCs) and bromine (from methyl bromide and halons). The chlorine and bromine free radicals react with ozone molecule and destroy their molecular structure, thus depleting the ozone layer. One chlorine atom can break more than one lac molecule of ozone, while bromine is 40 times more destructive than chlorine molecule.

Effects of the Ozone Hole

 Depletion of ozone layer and increase in UV rays can also cause DNA damage which can also be catastrophic. Thinning of ozone layer means getting direct in touch with ultra violet rays which can cause skin cancer or skin irritation which can lead to death. A decrease in 1% of ozone layer can cause 5% increase in cases of skin cancer.

Exposure to UV rays has also increased the cases of cataracts which in turn affects people’s vision and could also cause an increase in people becoming blind.

Aquatic plants and animals are also not safe. UV rays can penetrate through water and can kill small plants and animals. If ozone hole keep on expanding, there would be very few plants which means less food in the whole world.

The effect of the ozone hole and the damage done to the layer is still not very well understood. Apart from the gradual decrease of the ozone layer all over the world, there is little quantifiable evidence of new holes appearing any time soon. Even so, a number of countries have been working towards mitigating the damage.

CFC’s have been banned, especially in aerosol cans and various electrical appliances. There have been many conventions held to discuss the methods that will slowly phase out the use of the gases. However, this has been met with a great deal of resistance from industries that are based on the production and use of the gases.

One of widespread and long lasting effects has been the public awareness towards the environmental issues facing the planet. As one of the first major man-made problems to be discussed on a public forum, it set the ground for public opinion and action on issues such as pollution, greenhouse gases, global warming and the climate crisis.

It also sparked off renewed research about how weather patterns and natural phenomenon may be disturbed small changes in the atmosphere. Ozone depletion is not as serious as it once was, but nonetheless it has had an impact on the planet.

The ozone layer does not face rampant ozone depletion anymore, as most governments and environmental agencies have worked hard to reduce the emission of CFCs. This has proven to be a success and is the base for further work in reducing dangerous emissions.

 

 

  

Given that these risks exist even when the ozone layer absorbs about 98 percent of UV light, a future with an even thinner ozone layer is scary indeed. In the 1980s, this frightening prospect motivated the scientific community and policy makers of the world to address the issue of CFC production, which resulted in the 1987 Montreal Protocol. Policy makers from different industrialized countries signed this treaty as a pledge to reduce their CFC outputs. International Day for the Preservation of the Ozone Layer is celebrated each year on the anniversary date of the treaty, September 16th.

The efforts seem to be working. Reports show that by 2049, the ozone will recover to 1979 thickness, which is when scientists believe the hole began to form . Many scientists believe the Montreal Protocol is responsible for this joyous recovery.

 

 

 

 

[Swati Nagar]

This is good information about the ozone layer. I would be glad if you share the status of ozone layer and its monitoring in Indian context.