Q6(b). What do you understand by ozone hole, How is it formed and where has it been detected?

“The ozone layer is Earth’s natural sunscreen.” – UNEP

The ozone layer is a dense concentration of ozone gas located in the stratosphere, roughly between ten to fifty kilometres above the earth’s surface. It absorbs harmful ultraviolet radiation coming from the sun, especially ultraviolet B radiation, which can cause skin cancer, cataracts, immune system damage and ecological imbalance. When a significant thinning occurs in this protective layer, it is commonly referred to as an ozone hole.

How is the Ozone Hole Formed

Release of Ozone Depleting Substances

Human-made chemicals known as ozone depleting substances such as chlorofluorocarbons, halons, carbon tetrachloride and methyl bromide are the primary cause. These chemicals were widely used in refrigeration, air conditioning, aerosol sprays, fire extinguishers and industrial cleaning.

Transport to the Upper Atmosphere

After being released at the ground level, these chemicals slowly rise into the stratosphere because they are extremely stable and do not break down in the lower atmosphere.

Breakdown by Solar Radiation

When they reach the stratosphere, strong ultraviolet radiation breaks down these chemicals and releases highly reactive chlorine and bromine atoms.

Rapid Destruction of Ozone

These reactive atoms destroy ozone molecules through repeated chemical reactions. One chlorine atom released from a chlorofluorocarbon can destroy thousands of ozone molecules.

This chain reaction results in large scale thinning of the ozone layer.

Role of Polar Stratospheric Clouds

In winters, extremely low temperatures in the polar regions lead to the formation of polar stratospheric clouds. Chemical reactions on the surface of these clouds convert chlorine into its most destructive form. When sunlight returns in early spring, these chlorine compounds rapidly break down large quantities of ozone, producing what is known as the ozone hole.

Where Has the Ozone Hole Been Detected

Antarctica

The most severe ozone hole has been detected over Antarctica. It was first observed in nineteen eighty five by the British Antarctic Survey. During the months of September and October it can span an area as large as twenty to twenty five million square kilometres.

Arctic Region

A milder and more variable ozone thinning appears over the Arctic because temperatures are not as low as in Antarctica. However, unusually cold winters have occasionally created significant ozone loss.

Mid-Latitudes Including India

Moderate and gradual thinning of ozone has been detected across mid-latitude regions, including parts of Asia, Europe and North America. Though not as dramatic as the polar ozone hole, this thinning exposes populations to increased ultraviolet radiation.

The Montreal Protocol of nineteen eighty seven, one of the most successful environmental treaties, mandated a global phase-out of ozone depleting substances. According to the United Nations Environment Programme, the ozone layer is steadily recovering and is expected to return to its pre nineteen eighty levels between twenty forty and twenty sixty, depending on the region.