Understanding the Montreal Protocol

The question asks about the primary purpose behind the signing of the Montreal Protocol. This international treaty is a landmark agreement aimed at protecting the Earth's ozone layer.

Purpose of the Montreal Protocol

The Montreal Protocol, signed in 1987, is an international treaty designed to phase out the production and consumption of numerous substances that are responsible for depleting the ozone layer. The main culprits targeted by this protocol were:

• Chlorofluorocarbons (CFCs): These were widely used in refrigeration, air conditioning, aerosol propellants, and solvents.
• Other ozone-depleting substances (ODS) like halons, carbon tetrachloride, and methyl chloroform.

By controlling the emission of these harmful substances, the protocol aims to reduce the thinning of the ozone layer, which protects us from harmful ultraviolet (UV) radiation from the sun.

Why Other Options Are Incorrect

• Carbon Dioxide (CO₂): While a major greenhouse gas contributing to climate change, the Montreal Protocol's primary focus was not CO₂ emissions. Different international agreements, like the Kyoto Protocol and the Paris Agreement, address CO₂.
• Methane (CH₄): Methane is another significant greenhouse gas, but like CO₂, its control is addressed by climate change agreements, not primarily the Montreal Protocol.
• Sulphur Dioxide (SO₂): SO₂ is a major air pollutant associated with acid rain and respiratory problems. Its emission control is typically handled through national air quality regulations and specific protocols targeting air pollution, not the Montreal Protocol's ozone layer protection mandate.

Therefore, the substance the Montreal Protocol was specifically signed to control the emission of, among the options provided, is chlorofluorocarbons.