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Which group of chemicals was primarily responsible for the depletion of the ozone layer?
Chlorofluorocarbons (CFCs)
Carbon dioxide
Methane
Nitrogen oxides
Chlorofluorocarbons (CFCs)
Chlorofluorocarbons (CFCs) are anthropogenic organic compounds containing chlorine, fluorine, and carbon that were widely used in refrigeration and aerosol propellants. When released, they migrate to the stratosphere, where solar ultraviolet radiation breaks them down to release chlorine atoms, which catalytically destroy ozone molecules.
Chlorofluorocarbons (CFCs) are anthropogenic organic compounds containing chlorine, fluorine, and carbon that were widely used in refrigeration and aerosol propellants. When released, they migrate to the stratosphere, where solar ultraviolet radiation breaks them down to release chlorine atoms, which catalytically destroy ozone molecules.
Think of the chlorine radical like a 'wrecking ball' that keeps bouncing off buildings (ozone molecules), breaking them down one by one, while the ball itself remains intact to continue the destruction.
CFC = Chlorine Frees Chlorine (causing chaos)
CF2тАЛCl2тАЛ+h╬╜тЖТClтИЩ+CF2тАЛClтИЩ тАФ Photolytic decomposition of CFCs
ClтИЩ+O3тАЛтЖТClO+O2тАЛ тАФ Propagation step 1
ClO+OтЖТClтИЩ+O2тАЛ тАФ Propagation step 2
In the stratosphere, UV radiation breaks the CтИТCl bond in CFCs (e.g., CF2тАЛCl2тАЛ), releasing a highly reactive chlorine radical (ClтИЩ). This radical reacts with ozone (O3тАЛ) to form chlorine monoxide (ClO) and oxygen (O2тАЛ). Subsequently, the ClO reacts with free oxygen atoms to release the ClтИЩ radical again, allowing a single chlorine atom to destroy thousands of ozone molecules in a continuous catalytic cycle.
CFCs have a long atmospheric lifetime, allowing them to reach the stratosphere.
Ozone layer depletion leads to increased UV radiation reaching Earth's surface.
The Montreal Protocol is the international treaty aimed at phasing out CFC production.
Ozone depletion is most severe over Antarctica, famously known as the 'Ozone Hole'.
CFCs were non-toxic, non-flammable, and chemically stable, making them ideal for early industrial use.
High global warming potential (GWP).
Severe depletion of the stratospheric ozone layer.
Refrigerants in air conditioning and refrigerators
Propellants in aerosol spray cans
The ozone layer protects Earth by absorbing approximately 97-99% of harmful high-frequency UV radiation.
Option B (Carbon dioxide) is a greenhouse gas causing global warming but does not directly deplete ozone.
Option C (Methane) is a greenhouse gas that can actually participate in stratospheric chemistry but is not the primary cause of ozone destruction.
Option D (Nitrogen oxides) can contribute to ozone destruction but are naturally occurring and their anthropogenic emission is secondary to CFCs.
A is correct тАФ Chlorofluorocarbons (CFCs) act as catalytic agents that break down stratospheric ozone.
Always link ozone depletion to UV-B radiation; increased UV-B is known to cause skin cancer and cataracts in humans, which is a common focus in exam questions.