Question

Ozone hole is maximum over (a) Europe (b) Antarctica (c) India (d) Africa.

Short answer

The ozone hole is maximum over Antarctica.

Step-by-step solution

Understanding the Ozone Hole

The ozone hole refers to the region of significantly reduced ozone layer in Earth's stratosphere. It is a result of chemical reactions involving chlorine and bromine, primarily from man-made compounds. Understanding where the ozone hole is predominant helps identify the correct option.

Identifying the location with maximum Ozone Depletion

Various scientific studies and observations have concluded that the ozone hole is most prominent over Antarctica. This is due to the unique meteorological and chemical conditions present in the polar stratosphere of Antarctica which favor the formation of the ozone hole, particularly during the Southern Hemisphere's spring.

Key concepts

Stratosphere Ozone Depletion

The stratosphere is a layer of Earth's atmosphere located approximately 10 to 50 kilometers above the planet's surface, home to the ozone layer. This layer contains a high concentration of ozone (O3) molecules, which are vital in absorbing the majority of the sun's harmful ultraviolet (UV) radiation.

Ozone depletion in the stratosphere is a concerning environmental issue, predominantly caused by human-made chemicals such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons. These substances release chlorine and bromine atoms upon exposure to UV radiation, which then catalyze the breakdown of ozone molecules into oxygen (O2). This reaction is represented by the equation: \[\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2\].

Sustainable practices and international policies such as the Montreal Protocol aim to reduce the release of these ozone-depleting substances. Since its implementation, there's been a slow but positive progress in the recovery of the stratosphere's ozone layer.

Chemical Reactions in Ozone Layer

Understanding the chemical reactions within the ozone layer is central to comprehending why ozone depletion occurs. The primary destructive cycle involves chlorine or bromine atoms, which come from halogen source gases (e.g., CFCs and halons). These atoms act as catalysts, which means they are not consumed in the reaction and can continuously destroy ozone molecules.

The basic set of reactions involving chlorine is shown below: \[\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2\]\[\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2\].
The net result of these reactions is the conversion of one ozone molecule and one oxygen atom into two oxygen molecules, significantly reducing the ozone concentration. Similar reactions occur with bromine atoms, which can be even more destructive to ozone on a per-atom basis.

Antarctica Ozone Depletion

The ozone hole over Antarctica is a dramatic demonstration of large-scale atmospheric ozone depletion. The phenomenon is most pronounced during the austral spring (September to November) when the conditions for ozone destruction are optimum. This is due to several factors unique to the region, including the presence of polar stratospheric clouds (PSCs) and the isolation caused by the polar vortex – a large area of low pressure and cold temperatures encircling the South Pole.

PSCs provide surfaces for complex chlorine-bearing compounds to convert into reactive chlorine and bromine gases, which then participate in ozone-depleting reactions when sunlight returns to Antarctica in the spring.

Why is it More Pronounced in Antarctica?

Compared to other regions, Antarctica's extreme cold enables the formation of the aforementioned PSCs, and the strong polar vortex traps the substances involved in ozone depletion over the continent. As a result, when the Antarctic spring arrives, there is a rapid and large-scale depletion of ozone, leading to the creation of what is colloquially known as the 'ozone hole'.

Efforts like the Montreal Protocol have helped phase out the production of many substances that lead to ozone depletion, but the complete healing of the ozone layer, especially over Antarctica, is expected to take several decades.