Which of the following is not responsible for the destruction of the ozone…

Concept

Stratospheric ozone is depleted when long-lived halogen-containing compounds reach the stratosphere and ultraviolet light releases chlorine or bromine radicals. Those radicals participate in catalytic cycles, so one radical can transform many ozone molecules before it is removed.

A substance can still be a serious pollutant without belonging to this ozone-depletion pathway. The relevant test is whether its established atmospheric chemistry supplies reactive halogen radicals in the stratosphere.

Application

Apply that mechanism to each offered substance:

• CFCs are sufficiently stable to reach the stratosphere; ultraviolet radiation breaks them down and releases chlorine radicals.

• Halons can reach the stratosphere and release bromine radicals, which are highly effective in catalytic ozone reactions.

• HCFCs break down more readily than CFCs in the lower atmosphere, but the fraction that reaches the stratosphere can still release chlorine radicals.

• Dioxins are persistent chlorinated organic pollutants associated mainly with incomplete combustion and certain industrial processes; their established hazards are toxicity, persistence, and bioaccumulation in food chains.

Cross-check

The Montreal Protocol controls CFCs, halons, and HCFCs as ozone-depleting substances. Dioxins are instead addressed internationally as persistent organic pollutants under the Stockholm Convention.

Therefore, among the offered choices, Dioxins are not responsible for destruction of the ozone layer.