Choose the correct statement(s) about O₃ in atmosphere.
(A) O₃ steady state in troposphere depends on NO/NO₂ ratio. (B) A one percent decrease in overhead O₃ is expected to result in increase of 2 percent UV-C at ground level. (C) Ozone depleting potential is calculated with reference to CFC-111. (D) Halons do not cause catalytic destruction of O₃ in stratosphere. (E) HCl and ClONO₂ are catalytically active forms of chlorine in stratosphere.
Choose the correct answer from the options given below:

Correct option is C

Explanation:
· Statement A is correct: In the troposphere, ozone formation and destruction are primarily governed by the balance of nitrogen oxides (NO and NO₂), which participate in photochemical reactions controlling the O₃ steady state.
· Statement B is incorrect: A 1% decrease in stratospheric ozone typically results in a 2% increase in UV-B, not UV-C. UV-C is mostly absorbed before reaching the stratosphere.
· Statement C is incorrect: Ozone depleting potential (ODP) is calculated relative to CFC-11, not CFC-111.
· Statement D is incorrect: Halons do cause catalytic destruction of ozone in the stratosphere and have high ozone-depleting potential.
· Statement E is incorrect: HCl and ClONO₂ are reservoir species, not catalytically active forms. The active forms are Cl and ClO radicals.
Information Booster:
· The ozone layer protects life on Earth by absorbing harmful ultraviolet (UV) radiation. In the troposphere, ozone is a pollutant, while in the stratosphere, it acts as a protective shield. The O₃ balance is influenced by chemical species such as NOₓ, VOCs, and halogens. Chlorine and bromine radicals, mainly released from CFCs and halons, cause stratospheric ozone depletion through catalytic cycles.