Ozone layer is a layer in the Earth's atmosphere which is responsible for absorbing about

97-99% of the sun's UVB rays, which are the primary constituents of the sun's high

frequency ultraviolet rays and are potentially most damaging to terrestrial life forms! This

atmospheric layer is made up of a relatively high concentration of Ozone (O3) and is

located in the lower portion of the Stratosphere, marginally occupying the upper portion

of the Troposphere, and contains 90% of the Ozone in Earth's atmosphere! Ozone

layer depletion is a major cause for Global concern as this implies greater exposure to the

sun's damaging rays, which could be detrimental to all life forms on Earth! So, what is

Ozone layer depletion all about? Read on to know about Ozone layer facts and the causes

and effects of its depletion to get wiser!

Ozone Layer Depletion Facts

The Observations: The term "Ozone layer Depletion" is used in describing two

separate but related observations. The first observation is that there has been a slow but

steady decline, of about 4% every ten years, in the volume of Ozone in the Stratosphere

since the latter part of the 1970s. The second observation is that there has been a greater,

seasonal decline in the Stratospheric Ozone over the polar regions of the Earth during the

same time period. The second observation is what we generally refer to the Ozone Hole

(read Ozone layer: hole in the Ozone layer). Besides, Stratospheric Ozone depletion,

there are events of Tropospheric Ozone depletion as well which take place near the

surface during spring in polar regions.

Depletion Mechanism: The mechanism by which Ozone layer depletes over the

Polar Regions and over mid-latitude regions differ. However, one common process is

responsible for both kinds of depletion – the Ozone layer over both types of regions is

destroyed by catalytic actions of the halogen atoms, chlorine and bromine. Chlorine and

bromine are constantly released in the atmosphere in the guise of air pollutants and,

according to the US. Environmental Protection Agency, one atom of chlorine is capable

of destroying more than a hundred thousand Ozone molecules! Find out about these

two chemical elements in bromine vs chlorine.

Source of Halogen Atoms: The main reason behind the release of the above

mentioned halogen atoms in the atmosphere is

the photodissociation of freons and halons. Freons are Chlorofluorocarbon compounds, also

known as CFC, and halons are Bromofluorocarbon compounds. After being emitted on the

surface, these compounds rise and reach the Stratosphere, where they get down to destroying

the Ozone molecules, which are highly reactive themselves and pose an easy target to the

CFC and BFC compounds! Aerosols are primarily responsible for releasing CFC into the

atmosphere – so the next time you go shopping for deodorant, act responsibly and pick the

roll-on over the spray can.

Recognizing the Crisis: In the early part of the 1980s, Ozone layer depletion rate

was predicted to be 7% over a period of 60 years. The Ozone Hole was recognized and

widely reported by the print media in 1985. Prior to that, the detection of Ozone depletion

over Antarctica was dismissed as an error in measurement. Apart from the Antarctic

depletion, the only other considerably prominent Ozone layer depletion is observed as an

Ozone "dimple" over the North Pole during Arctic spring. Rate of decline of Ozone

volume over mid-latitude areas lesser that that over the Polar Regions.

Ozone Layer Depletion Causes

The chief cause behind Ozone layer depletion is CFC and halocarbon pollution.

The ultraviolet rays cause these gases to dissociate and release chlorine atoms which

destroy Ozone molecules in large quantities.

These CFCs and halocarbons are released in large quantities by aerosolized

products such as perfumes, deodorants, insecticides, fire extinguishers, etc. Moreover,

large fires and certain kinds of marine life forms are responsible for constantly releasing

chlorine which reaches the Stratosphere.

Polar Stratospheric Clouds (PSCs) also have a role to play in accentuating

chlorine's caliber to destroy ozone. The PSCs form during the winter months in the

extremely cold Polar Regions, which means 3 months of darkness with no instance of

solar radiation taking place during this time! This lack of sunlight leads to dipping

mercuric readings, allowing the polar vortex to trap and chill the air. The PSCs form

during this time and are of three types – nitric acid trihydrate cloud, gradually cooling

water-based-ice clouds and rapidly cooling water-based-ice clouds. All three types of

PSCs set the stage for chemical reactions which can lead to the destruction of the Ozone

layer!

The reason behind Ozone layer depletion being the fastest and most abundant

during polar spring is very interesting. During winter, the undisturbed PSC formation

ensures that sufficient chemical reservoirs are formed which contain compounds such as

Hydrochloric Acid and Chlorine Nitrate. During winter and spring, the surface reaction

on the PSCs transforms these compounds into reactive free radicals. With the advent of

spring, the sunlight powers these stored compounds towards photochemical reactions to

release the trapped compounds.

Ozone Layer Depletion Effects

Ozone layer and global warming share a closer relation that we can imagine.

Depletion of the Ozone layer straightaway means more exposure to the sun's harmful

UVB rays! The increased instances of skin cancer and cataracts these days are being

attributed major to higher exposure to UVB rays.

Increased ultraviolet radiation has shown detrimental results in the growth and

yield of crops. Certain food crops like rice are dependent upon cyanobacteria that live in

the roots, for retaining nitrogen, which is crucial for plant nutrition. These bacteria are

sensitive to UV radiation and high exposure adversely affects their growth and life cycle.

Serious negative developments have been observed in the reproductive rates of

various fish, crabs, shrimps and amphibians due to UV exposure. Reproduction cycle of

phytoplankton is also adversely affected by exposure to UVB rays. These unicellular

organisms make up the ocean bed and are a source of food and camouflage to many

marine life forms. A decline in their growth rate may compromise many dependent life

forms!

National Geographic states that 90% of the CFCs, the chief chlorine pollutant and culprit

responsible for Ozone layer depletion, that are present in the atmosphere till date, were

emitted by industrialized countries in the Northern hemisphere. These countries banned

CFC in 1996 and the result of this joint effort can already be seen in the form of a

decrease in atmospheric chlorine. The damage may have been considerable but it is not

too late. We, as individuals, can do our part by increasing our awareness on ozone layer

depletion: effects and causes of ozone depletion and avoiding the use of products which

are potential chlorine-based atmospheric pollutants. Be aware, act responsibly and

breathe easy!