Question

What is denitrification in the context of ozone depletion, and why is it important?

Group of answer choices

a) Denitrification is the significant lowering of the concentration of N₂ (g) in the stratosphere. This process is crucial to ozone formation, as it creates space in the stratosphere for formed ozone to reside.

b) Denitrification is the removal of NO₂ (g) from the stratosphere. This process increases ozone depletion, since it prevents ClO (g) from being stored as catalytically inactive ClONO₂ (g)

c) Denitrification is removal of NO (g) from the stratosphere. This is important because NO can act as a significant X catalyst and drive ozone depletion.

Answer 1

Answer :

Ozone (O₃) is molecule formed by three atoms of oxygen. It is found in the upper part of the atmosphere called stratosphere. It acts as a shield absorbing ultraviolet radiation from the Sun. UV rays are highly injurious to living organisms since DNA and proteins of living organisms preferentially absorb UV rays, and its high energy breaks the chemical bonds within these molecules.

Ozone gas is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere. There should be a balance between production and degradation of ozone in the stratosphere. The balance has been disrupted due to enhancement of ozone degradation by chlorofluorocarbons (CFCs). CFCs find wide use as refrigerants. CFCs discharged in the lower part of atmosphere move upward and reach stratosphere. In stratosphere, UV rays act on them releasing Cl atoms. Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts; Cl atoms are not consumed in the reaction. Hence, whatever CFCs are added to the stratosphere, they have permanent and continuing effects on Ozone levels. Although ozone depletion is occurring widely in the stratosphere, the depletion is particularly marked over the Antarctic region. This has resulted in formation of a large area of thinned ozone layer, commonly called as the ozone hole.

Denitrification in ozone depletion :

Denitrification may be defined as the permanent removal of N0y from an air by the gravitational sedimentation of NOy-containing particles. Denitrification reduces the formation rate of NOx and slows the rate of ClO_X deactivation to ClONO₂, extending the O₃ loss period. That means, Denitrification is the removal of NO₂ (g) from the stratosphere. This process increases ozone depletion, since it prevents ClO (g) from being stored as catalytically inactive ClONO₂ (g).

Denitrification may reduce halogen activation as an airmass depleted in HNO₃ has a reduced potential for forming the Polar stratospheric clouds (PSCs) which catalyse the heterogeneous activation reactions.

The PSC formation threshold is sensitive to gas-phase HNO₃ and H₂O concentrations and early denitrification may reduce the formation of PSCs and suppress the heterogeneous activation of halogens. Therefore, denitrification is important in the ozone depletion.