Final answer:
Halogens, particularly chlorine and bromine, are destructive to ozone and their presence in the stratosphere is due to human-made chemicals called ozone-depleting substances. A single chlorine atom can destroy ozone molecules for an extended period, leading to increased UV radiation reaching Earth.
Step-by-step explanation:
True, halogens, particularly chlorine and bromine gases, are highly reactive with ozone and can cause its destruction in the stratosphere. This process involves the release of chlorine and bromine from substances like CFCs, leading to a reaction with ozone molecules resulting in their depletion. The presence of chlorine and bromine in the upper atmosphere is largely due to anthropogenic activities, primarily the release of substances known as ozone-depleting substances (ODS), which include chlorofluorocarbons (CFCs) used in refrigerants, air conditioning systems, foams, and aerosols.
Molina and Rowland demonstrated that chlorine atoms from CFCs catalyze a cycle of reactions that break down ozone molecules. When CFCs are exposed to UV light or react with hydroxyl radicals, chlorine atoms are released. These chlorine atoms participate in a catalytic cycle that repeatedly destroys ozone without being consumed, with one chlorine atom capable of destroying ozone molecules for up to two years before it is removed from the stratosphere. This disruption to the ozone layer allows higher levels of UV radiation to penetrate to Earth's surface, which can have harmful effects on human health and ecosystems.
The Montreal Protocol has been an effective international agreement in reducing the production and release of ODS, which has positively impacted the rate of ozone depletion. However, the ozone layer continues to be at risk, and continued vigilance and international cooperation are necessary to minimize further damage.