Ozone Depletion Causes

Ozone layer depletion is one of the most important and widely discussed environmental issues. Ozone is basically a gas that forms a protective covering in the Earth's upper atmosphere, which is known as stratosphere. The depletion of this protective layer was first noticed in the year, 1970. Ozone is formed when three oxygen atoms combine together. The process begins when an oxygen molecule absorbs ultraviolet photons and breaks down into two oxygen atoms. This process is known as photolysis or photo dissociation. The free oxygen atom then combines with one oxygen molecule to form a molecule of ozone (O3).

The importance of the ozone layer lies in the fact that it prevents the ultraviolet radiation of the sun between 310 to 200 nm wavelength from reaching the Earth by absorbing these harmful radiations. While doing so, an ozone molecule breaks down into a molecule of oxygen and an oxygen atom. But, the free oxygen atom again combines with an oxygen molecule to form one ozone molecule. Thus, its formation and destruction is a continuous process, which helps to keep its total amount at a balanced level. But, certain substances can disrupt this process and cause its layer to deplete. Ozone depletion and ozone hole are two related, but distinct condition. The exact mechanisms of ozone depletion and the formation of hole in the ozone layer in the polar regions are different, but both involves the destruction of ozone layer by substances like, atomic chlorine and bromine.

Reasons Behind Ozone Depletion

The depletion is due to the increase in the level of atomic chlorine and bromine, as well as the rising levels of free radicals like, hydroxyl radicals and nitric oxide radicals. The most important ozone depleting substances are, chlorofluorocarbon or CFC, bromofluorocarbon or halons, methyl chloroform, methyl bromide and hydrofluorocarbons. Out of these, chlorofluorocarbons are the most important substances responsible for depleting this layer. In Earth's atmosphere, i.e. in lower atmosphere chlorofluorocarbons are very stable and hence do not break down easily. But, when these CFC are transported to the stratosphere, they are broken down by the actions of the ultraviolet radiation of the sun.

When CFCs are broken down, they release free chlorine atoms. A free chlorine atom released thus, reacts with an ozone molecule to form chlorine monoxide. In the process, an oxygen molecule is also released. Now, the chlorine monoxide reacts with ozone to form a free chlorine atom, along with two oxygen molecules. The free chlorine atom again reacts with ozone and repeats the series of chemical reactions, which leads to the depletion of the ozone layer. Similarly, the other halogen atoms, like free bromine atoms, released due to the breakdown of methyl bromide and halons also deplete the ozone layer.

Chlorofluorocarbons are mainly found in industrial solvents and spray aerosols, perfumes, deodorants, insecticides, and they are also used in foam products, refrigerators, air conditioners and freezers. The use of CFC has been however, cut down significantly after the Montreal Protocol.

Halons are primarily used in fire extinguishers, while methyl bromide is a pesticide. Methyl chloroform on the other hand, is used as a solvent in various industrial processes. Other ozone depleting substances like, carbon tetrachloride is used as a solvent and in fire extinguishers. Hydrofluorocarbons are nowadays used to substitute CFCs due to the fact that, they are less harmful to the ozone layer than CFC. But, hydrofluorocarbons are green house gases that again causes global warming.

Ozone Layer Depletion Effects

Ozone when present in the lower atmosphere is considered as a pollutant and green house gas. Green house gases are known to contribute to climate change and global warming. But, in the stratosphere, ozone serves a very special purpose by absorbing the harmful ultraviolet radiation of the sun. These radiations can significantly increase the risk for certain types of skin cancer like, malignant melanoma, basal and squamous cell carcinoma. Even the incidence of cortical cataracts and blindness can increase with the increased exposure to ultraviolet rays. If excess of ultraviolet B radiation reach the Earth, it can adversely affect reproduction, mobility and orientation of the microscopic living organisms, known as phytoplankton. Phytoplanktons are found at the bottom of the aquatic food chain and hence, reduction in their population can create imbalance in the entire food chain, and affect the population of other organisms too. This depletion can also affect cyanobacteria, which help food crops like, rice to utilize atmospheric nitrogen.

It is true that a lot of damage has already been caused to the ozone layer. But, it is still possible to reverse this process, if all the nations cooperate and come together to reduce the level of industrial emission of CFCs and other ozone depleting substances.

In this regard, Montreal Protocol has been adopted in the year 1987, and with proper implementation of the provisions of the Montreal protocol, recovery is expected by 2050. The emission of CFC has already been reduced significantly since the adoption of Montreal protocol. The need of the hour is to create greater awareness about the causes of ozone depletion, as well as take urgent steps for mitigating this problem.