Ozone: The shield of the Earth
Weakening of the shield, more intense UV-b and UV-a radiation exposure at the surface would lead to quicker sunburn, skin cancer, cataracts in the eye and even reduce crop yield in plants.

BySanjenbam Jugeshwor Singh

Updated on 4 Oct 2021, 2:55 am

Representational Image (Photo: Pixabay)

Representational Image (Photo: Pixabay)


Ever wondered why cancer rates have tripled in the last 20 years across the world, eye cataracts are increasing and crop yields are falling? Well, life on Earth would not be possible without sunlight. But the Energy emanating from the sun would be too much for life on Earth to thrive, were it not for the Ozone layer.

Ozone (O3) is a molecule made up of oxygen (O) and it is mostly found in the stratosphere, which protects us from the sun’s harmful Ultraviolet (UV) radiation. Although it represents only a tiny fraction of the atmosphere, Ozone is crucial to life on Earth. Ozone in the stratosphere –a layer of atmosphere between 15 to 50 kms ( 10 and 31 miles) above us – acts as a shield to protect Earth’s surface from the harmful Ultraviolet radiation. Without ozone, the Sun's intense UV radiation would sterilize the Earth’s surface.

Ozone is lethal to almost all viruses, bacteria, fungus and cancer cells. So weakening of the shield, more intense UV-b and UV-a radiation exposure at the surface would lead to quicker sunburn, skin cancer, cataracts in the eye and even reduce crop yield in plants.

However, near the surface where we live and breathe, Ozone is a harmful pollutants that causes damage to lung tissues and plants particularly a family of gases called nitrogen oxide (released from vehicle and industry during the combustion process) and with volatile organic compounds (Carbon-containing chemicals that evaporates easily into the air, such as petroleum products).

The poisonous ozone levels reported affecting our cities differs dramatically in that it represents the combining of the extensive overwhelming pollution with ozone insufficient to do the job. If you wonder why cancer rates have tripled in the last 20 years, consider this starling fact. The oxygen level of the air we breathed 200 years ago is much higher than it is today.

The discovery and naming of Ozone is attributed to Christian Friedrian Schonbeing in 1840. Ozone is created primarily by sunlight or a strong electrical field on oxygen. When high energy ultraviolet rays (UV-c) strike on oxygen molecules (O2) they split the molecules into two single oxygen atoms, known as atomic oxygen. A freed oxygen atom then combines with another oxygen molecule to form a molecule of Ozone (O3). Because there is so much oxygen in our atmosphere this "Ozone-Oxygen cycle" is continuously absorbing high energy ultraviolet radiation (UV-c) and completely blocking it from reaching the Earth’s surface. This process creates heat which warms the upper part of the stratosphere.

Ozone is also formed in our atmosphere naturally by the effect of lightning on oxygen. It is that wonderful sweet smell that you can detect after a summer storm. It is nature’s method of cleansing our atmosphere of contamination. Ozone is very reactive and attacks other molecules in the air, often regenerating oxygen in the process. Also- and this is why ozone is important to us. Ozone in the stratosphere absorbs much of the sun’s UV-b rays, splitting back into molecules and atomic oxygen. No matter how the oxygen atoms are produced, they almost always quickly react with oxygen molecules reforming ozone. So while ozone is continuously being replenished, it is also continually being destroyed. Sometimes ozone molecules react with an oxygen atom, creating two oxygen molecules, thus ending the cycle.

Scientists have found that ozone levels change periodically with regular natural cycles such as the changing seasons, winds and long time scale sun variations. Ozone also responds to some sporadic solar events such as flares, moreover volcanic eruptions may injects materials into the stratosphere that can lead  to increased destruction of ozone. In the 1970s, scientists suspected that reactions involving man-made chlorine containing compounds upset this balance leading to lower levels of ozone in the stratosphere. The ozone destroyed by man-made emissions is comparable or more than the amount destroyed by natural processes. Human production of chlorine-containing chemicals such as Chlorofluorocarbon (CFCs) has added an additional factor that destroys ozone.

CFCs are molecules made up of chlorine, fluorine and carbon.  Because they are extremely stable molecules, CFCs do not react with other chemicals in the lower atmosphere, but exposure to ultraviolet radiation in the atmosphere breaks them apart, releasing chlorine atoms. Free chlorine atoms then react with ozone molecules, taking one oxygen atom to form chlorine monoxide (ClO) and leaving an oxygen molecule (O2 ). If each chlorine atom released from CFC molecule destroyed one ozone molecule, CFCs would pose very little threat to the ozone layer.

However when a chlorine monoxide molecule encounters a free atom of oxygen atom, the oxygen atom breaks up the chlorine monoxide stealing the oxygen atom and releasing the chlorine atom back into the stratosphere to destroy another ozone molecule. These two reactions happen over and over again so that the single atom of chlorine acting as a catalyst, destroys many molecules (about 1000,000) of ozone. Fortunately, chlorine atoms do not remain in the stratosphere forever. Free chlorine atoms react with gases such as methane (CH4) and get built up into hydrogen chloride (HCl) molecules. These molecules eventually end up back in the troposphere where they are washed away by rain. Therefore if humans stop putting CFCs and other ozone destroying chemicals into the atmosphere, stratospheric ozone will eventually return to its earlier higher value.

Ozone in the stratosphere absorbs most of the ultraviolet radiation from the Sun thus ozone screens all of the most energetic UV-c radiation and most of the UV-b radiation. Although ozone high up in the stratosphere provides a shield to protect life on Earth, direct contact with ozone is harmful to both plants and animals including humans. Every year, since at least 1978, there has been a sudden rapid decrease in the stratosphere ozone levels at the end of the Arctic winter. Scientists have found an ozone hole in the stratosphere.

Ozone hole is not really a hole but a thinning of the ozone layer over the South Polar Region. To address this problem on December 19, 1994, U.N General Assembly declared September 16 as the International Day for the preservation of Ozone layer since then, September 16 is observed as World Ozone day with a specific theme every year. The theme of this year’s Ozone Day is keeping us, our Food and Vaccine Cool.

The significance of ozone layer preservation Day is way more than many other smaller issues around the world. The layer protects harmful UV rays and indirectly prohibits global warming. This can be a huge problem and difficult to tackle. Hence the ozone layer is highly significant in the well-being of the planet Earth.

First published:3 Oct 2021, 7:50 pm


Sanjenbam Jugeshwor Singh

Sanjenbam Jugeshwor Singh

Faculty, JCRE Global College, Imphal, Manipur. The writer can be reached at sjugeshwor7@gmail.com

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