- Ozone is a molecular form of oxygen with 3 oxygen atoms.
- In the stratosphere, ozone is being created by the absorption of short wavelength ultraviolet radiations which decomposes molecular oxygen into atomic oxygen.
- The atomic oxygen then reacts with molecular oxygen to form ozone.
- Ozone thus formed distributes itself in the stratosphere and absorbs harmful ultraviolet radiations and is continuously being converted back to molecular oxygen.
- The Ozone concentration in stratosphere is about 10 parts per million compared to 0.05 ppm concentration of tropospheric ozone.
- The stratospheric Ozone concentration is disturbed by reactive atoms of chlorine, bromine etc., which destroy ozone molecules and result in thinning of ozone layer generally called ozone hole.
Thinning of Ozone Layer
- Generally Ozone depletion is observed during spring season of South Pole.
- Since mid-1970s there is a steep decline in the concentration of ozone.
- CFCs are released in the troposphere and reach the stratosphere and remain there for 65 to 110 years destroying ozone molecules.
- In 1985 scientists for the first time discovered that 50% (98% in some areas) of upper stratospheric ozone over Antarctica had got destroyed during Antarctic spring and early summer.
- A similar scenario of destruction of ozone is seen on the North Pole during the Arctic spring and early summer.
- However, the depletion here is 10-25%.
What causes Ozone Depletion?
- Chlorofluorocarbons (CFCs) are mainly responsible for ozone depletion in the stratosphere.
- CFCs are used as coolants in refrigerators and air conditioners, as propellants, cleaning solvents, sterilisers and in styrofoam etc.
- Nitrous oxide released during denitrification of nitrates also destroys stratospheric ozone.
- Further bromine atoms also destroy hundred times of more ozone molecules than chlorine atoms.
- Bromine in the form of hydro-bromic fluorocarbons (HBFCs) are used in fire extinguishers and methyl bromide is used as a pesticides.
Steps to contain Ozone Depletion
- The Vienna Convention for the Protection of the Ozone Layer was agreed upon at the Vienna Conference of 1985.
- It acts as a framework for the international efforts to protect the ozone layer.
- However it does not include legally binding reduction goals for the use of CFCs.
- The Montreal Protocol is a protocol to the Vienna Convention for the Protection of the Ozone Layer.
- Adopted in 1987 it is a legally binding treaty designed to protect the ozone layer by phasing out the production of numerous substances mainly CFCs that are responsible for ozone depletion.
- Since 2010, the agenda of the Protocol has focused on the phase-out of hydrochloroflurocarbons.
About Kigali Agreement
- A historic global climate deal was reached in Kigali, Rwanda in 2016.
- Kigali Agreement amended the1987 Montreal Protocol to phase out Hydrofluorocarbons (HFCs) by the late 2040s.
- Set to enter in to force on 1 January 2019, the Kigali Amendment calls for slashing the future use of HCFC gases in refrigerators, air conditioners and related products.
- Nations that ratify the Kigali Amendment are committing to cutting the projected production and consumption of hydrofluorocarbons (HFCs), by more than 80 percent by 2045.
- Now according to the report by implementing Kigali agreement global warming can reduce up to 0.5°C of global warming this century.
- HCFCs are potent greenhouse gas mainly used in cooling and refrigeration applications and in the manufacture of foam products.
Section : Environment & Ecology