Ozone Hole — Prelims Strategy

Prelims Strategy

Memorise the causal sequence with its conditions: persistent source gases reach the stratosphere; reactive halogen chemistry becomes possible; polar cold and clouds prepare the setting; returning sunlight enables rapid loss. Reject explanations based on a physical gap, simple displacement by carbon dioxide or lower-atmosphere rain washout. Keep reservoir forms distinct from the active species involved in catalytic cycles.

Separate Montreal and Kigali functions. Montreal began in 1987 with ozone-depleting-substance controls; Kigali in 2016 concerns HFC phasedown for climate reasons. Do not confuse HFCs with HCFCs, or infer that a climate benefit makes Kigali part of the Paris commitment mechanism.

For data statements, identify the metric and domain. Below 220 DU defines the monitored area threshold, while the minimum column measures a different aspect. The 2022 recovery projections refer to 1980 values and differ across near-global, Arctic and Antarctic domains. An annual change cannot alone prove a complete long-term recovery or its failure. Read conditional language and geographical limits as part of the fact.