Which substance is most closely associated with ozone destruction in the stratosphere as a catalyst, not consumed in the reaction?

Which substance is most closely associated with ozone destruction in the stratosphere as a catalyst, not consumed in the reaction?

• A. Oxygen
• B. Chlorine
• C. Nitrogen oxides
• D. Carbon dioxide

Answer: (B)

Ozone destruction in the stratosphere often happens through catalytic cycles, where a species helps break ozone apart but is itself regenerated to continue destroying more ozone molecules. That makes the substance a true catalyst: it participates, is not consumed, and can keep acting again and again. Chlorine from human-made chlorofluorocarbons enters the stratosphere and starts a classic two-step cycle. First, a chlorine atom reacts with ozone to form chlorine monoxide and oxygen. Then chlorine monoxide reacts with a free oxygen atom to release another oxygen molecule and regenerate the chlorine atom. Net effect: ozone plus a free oxygen atom becomes two oxygen molecules, and the chlorine atom is left ready to repeat the process. Because the chlorine atom is regenerated, it can destroy many ozone molecules before it’s removed from the cycle, which is why chlorine is so closely associated with ozone depletion. While oxygen is involved in these reactions and nitrogen oxides can also catalytically destroy ozone, chlorine is the most prominent catalyst linked to stratospheric ozone loss, especially in the context of human-caused depletion. Carbon dioxide doesn’t serve as a catalyst in this ozone-destroying cycle.

Ozone destruction in the stratosphere often happens through catalytic cycles, where a species helps break ozone apart but is itself regenerated to continue destroying more ozone molecules. That makes the substance a true catalyst: it participates, is not consumed, and can keep acting again and again.

Chlorine from human-made chlorofluorocarbons enters the stratosphere and starts a classic two-step cycle. First, a chlorine atom reacts with ozone to form chlorine monoxide and oxygen. Then chlorine monoxide reacts with a free oxygen atom to release another oxygen molecule and regenerate the chlorine atom. Net effect: ozone plus a free oxygen atom becomes two oxygen molecules, and the chlorine atom is left ready to repeat the process. Because the chlorine atom is regenerated, it can destroy many ozone molecules before it’s removed from the cycle, which is why chlorine is so closely associated with ozone depletion.

While oxygen is involved in these reactions and nitrogen oxides can also catalytically destroy ozone, chlorine is the most prominent catalyst linked to stratospheric ozone loss, especially in the context of human-caused depletion. Carbon dioxide doesn’t serve as a catalyst in this ozone-destroying cycle.