For those born before the year 2k, you would have heard of the constant cry about how the ozone layer is depleting. The Earth’s atmosphere has 5 main layers, namely the Troposphere, Stratosphere, Mesosphere, Thermosphere and the Exosphere. The Troposphere is the layer supporting life and constitutes the layer for the first 12 km above the surface of the Earth. Since the direct contact of the sun’s rays have harmful UV rays that can cause skin cancer, destroy water ecosystems, damage eyes and even suppress the immune system. The ozone layer in the Earth’s Stratosphere, filters out most of the harmful UV radiation before it can reach the Troposphere. Thus the ozone layer is also called the ozone shield, because of its ability to absorb 7-99% of the harmful UV rays.1
The ozone formation cycle:
Ozone is produced in the atmosphere in a two-step process.
- The ultraviolet rays from the sun collide with oxygen molecules (O2), breaking them down into separate oxygen atoms
- These oxygen atoms then bind with other oxygen molecules to form ozone (O3)
Most of the ozone is produced in the higher end of the stratosphere and each day 400 million metric tons of ozone is produced. 2 The total ozone estimated is 3 billion metric tons, thus 12% of the ozone is produced by the sun every day.
Another third step to the ozone cycle is its removal. The ozone molecule might re-join with another oxygen atom to form 2 oxygen molecules.
Why the Ozone is depleting:
The major reason for the depletion of the ozone layer is Chlorofluorocarbons (CFC). It is an organic compound that contains chlorine, fluorine and carbon. In the early 1900s, coolants used in refrigeration appliances were extremely poisonous. A small leak from a refrigerator could potentially kill a person. CFC was developed in the 1930’s as a substitute to ammonia and was used in applications of refrigeration, spray cans, health care products and fire extinguishers. During the initial phases of its discovery, it was tagged as safe and non-toxic. In 1970s, scientists reported a steady decline in the ozone layer. It wasn’t until 1864 that the hole in the ozone layer was discovered.
While CFCs are safe to life forms in the troposphere, over time they rise up to the stratosphere where 90% of the ozone layer resides. The CFC’s then react with the UV rays of the sun, causes the carbon-chlorine bond to break, forming chlorine atoms.
This chlorine atom now collides with the ozone molecule pulling out an oxygen atom forming ClO and converts ozone to an oxygen molecule (O2).
Again the ClO atom reacts with an oxygen atom forming a Cl and oxygen molecule. Hence the cycle continues and Cl acts as a catalyst to the removal process of ozone. CFCs could stay in the atmosphere for years; thus even one stray chlorine atom can cause a lot of damage to the ozone layer.
5 Severe consequences of Ozone depletion
- Skin diseases – Since the sun’s rays reaching the Earth have unfiltered UV radiation, it is harmful to living organisms. People living in areas of thin ozone shields, have a slightly increased risk of skin cancer and burns due to prolonged exposure of sunlight. Vaguely put, the UV rays interfere with the replication of the DNA, leading to skin cancer. This kind of cancer is said to be treatable and is rarely fatal.
- Cataracts – It is a condition wherein a hazy layer is formed on the cortex or the eye lens. UVB rays are said to have a direct connection with cataracts resulting in blurry vision.
- Increase in Vitamin D production – Our skin synthesizes vitamin-d when it is exposed to sunlight. Exposure to unfiltered sunlight can cause over production of Vitamin-D thus increasing calcium levels in the blood. This further increases mortality rate. A normal human body however, has a mechanism to deal with over production of Vitamin-D
- Plant Growth – Crops rice that constitute a lot of the staple diet in many Asian countries depends on bacteria called Cyanobacteria for the retention of nitrogen. This bacterium survives through photosynthesis and UV rays tend to destroy such bacteria. Plants are also not quite adaptable to the increase in UV.
- Effects on Marine ecosystems – Even a small amount of exposure to UVB rays hamper the development of aquatic life. These organisms have a much lower reproductive capabilities thus leading to a sharp decrease in marine life.
Effect of the Montreal Protocol
In 1973, chemists Frank Rowland and Mario Milano of the University of California, Irvine researched and documented the damage done by CFCs on the ozone layer. The duo made a strong case and received a strong funding from the U.S. government. By 1976, the U.S. National Academy of Science backed the credibility of their report. Citing all the above dangers of a thin ozone layer, on 26 August 1987 more than 30 countries signed the Montreal Protocol. This protocol weeded out the use of most substances that were potentially harmful to the ozone layer. Majorly the banned substances were the ones containing chlorine and bromine. One substance that has not yet been added to this list is nitrous oxide. Later in 1995, Frank Rowland and Mario Milano received the Nobel prize for their work in chemistry.
With the Ban of CFCs, the ozone layer is finally repairing itself. Scientists suggest that the ozone layer will be like the 1980s level by 2040. This is one of the few times the international community has joined hands and achieved something so significant. We are still yet to deal with the greenhouse effect, but this has been a good step forward into saving the world (not that we had a choice).
You can see how the ozone layer is doing on the NASA website.