MP Board · Class 10 · Science · Our EnvironmentWhat is ozone? Where is it located in the atmosphere, and why is its depletion a cause for concern? Explain the role of CFCs in ozone depletion and mention preventive measures taken globally.

Introduction to Ozone\nOzone ($O_3$) is a molecule formed by three atoms of oxygen. Unlike normal oxygen molecule ($O_2$) which is essential for aerobic respiration, ozone is a deadly poison at the ground level. However, at higher levels of the atmosphere, it plays a vital protective role for life on Earth.

Location in the Atmosphere\nOzone is found naturally in the stratosphere, which lies at an altitude of about 15 km to 50 km above the Earth's surface. This region is commonly known as the ozone layer or ozonosphere.

Protective Role and Concern over Depletion

• Filtering UV Rays: The ozone layer absorbs harmful ultraviolet (UV) radiations coming from the Sun, preventing them from reaching the Earth's surface.
• Harmful Effects of UV Radiation: If UV rays reach the Earth, they can cause severe health hazards such as skin cancer, cataracts in human eyes, suppression of the human immune system, and severe damage to agricultural crops and marine phytoplankton.

Role of Chlorofluorocarbons (CFCs) in Ozone Depletion\nThe primary cause of ozone layer depletion is the excessive release of synthetic chemical compounds known as Chlorofluorocarbons (CFCs) into the atmosphere.

• CFCs are widely used as refrigerants, in aerosol spray propellants, and in fire extinguishers.
• When CFCs reach the stratosphere, ultraviolet rays break them down, releasing reactive chlorine atoms ($Cl$).
• A single chlorine atom acts as a catalyst and can react with and break down thousands of ozone molecules into oxygen, thereby thinning the ozone layer significantly, famously referred to as the 'ozone hole'.

Global Preventive Measures\nRecognizing the severe danger of ozone depletion, the United Nations Environment Programme (UNEP) successfully forged an agreement in 1987 known as the Montreal Protocol. Under this international treaty, all signatory countries agreed to freeze and phase out the global production and consumption of ozone-depleting substances, particularly Chlorofluorocarbons (CFCs), replacing them with safer environmental alternatives like Hydrofluorocarbons (HFCs).