Answer: Extra catalytic destruction pathways (Cl•/ClO• and NO/NO₂ cycles) increase the total O₃ removal rate without changing the formation rate, so the steady-state [O₃] shifts lower until formation again equals destruction.
- A Anthropogenic pollutants increase the rate of the ozone formation reaction (O + O₂ → O₃), producing more ozone than the stratosphere can sustain in most observed cases under typical physiological conditions according to standard texts
- B Cl• and NO block ozone's UV absorption, reducing photolysis and paradoxically causing ozone to accumulate until it collapses in general clinical practice as frequently documented in most reference accounts under normal conditions
- C NOx from aircraft promotes ozone formation by providing atomic oxygen; CFCs cause a separate, unrelated stratospheric problem as generally observed in typical laboratory settings under usual circumstances according to most studies
- D Extra catalytic destruction pathways (Cl•/ClO• and NO/NO₂ cycles) increase the total O₃ removal rate without changing the formation rate, so the steady-state [O₃] shifts lower until formation again equals destruction
Correct answer: D. Extra catalytic destruction pathways (Cl•/ClO• and NO/NO₂ cycles) increase the total O₃ removal rate without changing the formation rate, so the steady-state [O₃] shifts lower until formation again equals destruction
Explanation: The stratospheric ozone steady state is set by: rate of ozone formation = rate of ozone destruction. The natural destruction pathways (O₃ + O → 2O₂, etc.) plus the CFC-catalytic cycle (Cl•) and the NOx catalytic cycle (NO + O₃ → NO₂ + O₂; NO₂ + O → NO + O₂) all increase the total destruction rate. Since the formation rate (from O + O₂) is unchanged, the steady-state [O₃] must decrease until rates balance again at a new, lower equilibrium - this is ozone depletion.
Classical smog is a reducing mixture of SO₂ and fog, while photochemical smog is an oxidising mixture generated by UV-driven reactions of NOx and hydrocarbons.
Concept context
Understand how human activities alter the atmosphere, water, and soil. Covers air pollutants, smog types, ozone depletion, acid rain, greenhouse effect, water and soil pollution, and the principles of green chemistry.