One molecule of chlorine can destroy 100,000 ozone molecules.

• A. True
• B. False
• C. Not sure
• D. It depends

Answer: (D)

Chlorine acts as a catalyst in ozone destruction, so one chlorine atom can attack many ozone molecules through catalytic cycles. The basic cycle is Cl + O3 -> ClO + O2, followed by ClO reacting with another species (often an oxygen atom) to regenerate Cl and produce more O2. Because the chlorine atom is regenerated, it can destroy additional ozone molecules repeatedly. This means a single chlorine atom has the potential to remove a large number of O3 molecules.

But the exact number isn’t fixed. chlorine can become locked up in reservoir forms like ClONO2 or HCl, which removes it from the catalytic cycle until those reservoirs are broken apart. How much chlorine remains in the active form depends on atmospheric conditions such as NOx and HOx levels, temperature, sunlight availability, and the presence of other halogens. Under different conditions, the same chlorine atom might destroy many thousands of ozone molecules or far fewer, so the answer is that it depends.