Question

How is the ‘ozone oxygen cycle’ maintained in the stratosphere and state what disturbs the balance, resulting in ozone depletion or destruction, Give balanced equation for the same.

Answer 1

Ozone-oxygen cycle: “Breaking of ozone into O₂ in the stratosphere and making of ozone from oxygen in stratosphere and to maintain total concentration of ozone almost the same is called ozone-oxygen cycle.” Breaking of O₂ to form O_3.

\[\ce{->[U.V][light] O2 ->\underset{\text{oxygen atoms}}{[O] + [O]}}\]

\[\ce{O2 + [O] -> O3}\]

Photolysis : 0₂ [molecule] in presence of U.V. from sunlight in stratosphere breaks into [0] atom [very reactive].
0₃ is broken down [with the help of U.V. rays] into O₂ + [O]
U.V. rays → O3 → O₂ + O
O + [O] → O₂molecules and O3 + [O] → 2O₂
Very reactive oxygen atoms

\[\ce{[O2] + [O] ->[U.V. rays] O3 [ozone]}\]

Combine to produce in stratosphere

Depletion or destruction of ozone is due to increased level of [Cl], [Br], [NO], [OH] free radicals
These free radicals are highly reactive and attack 03 and deplete 03
Cl[g] + O₃[g] → C10[g] + O₂
C10[g] + O[g] →4 Cl[g] + 0,[g]
NO + O₃→4 NO₂ + O₃
NO₂+ O₃ → NO₃ + O₂
In this way cause depletion of ozone.