Ozone Depletion in the Stratosphere Questions in English

(B) The given figure is a satellite image showing the depletion of the ozone layer over the Antarctic region,commonly referred to as the 'Ozone hole'.
This phenomenon is characterized by a significant reduction in the concentration of ozone $(O_3)$ in the stratosphere over Antarctica,which is clearly visible in such satellite imagery as a dark central region.

(C) Chlorofluorocarbons $(CFCs)$ are human-made chemicals that were widely used as refrigerants in refrigerators and air conditioners.
They are stable compounds that reach the stratosphere,where they are broken down by ultraviolet radiation to release chlorine atoms.
These chlorine atoms cause the degradation of ozone $(O_3)$ molecules,leading to the depletion of the ozone layer.

(D) The ozone layer in the stratosphere acts as a shield by absorbing harmful ultraviolet $(UV)$ radiation from the sun.
Ozone depletion (often referred to as the ozone hole) allows more $UV$ radiation to reach the Earth's surface.
Increased exposure to $UV$ radiation is known to cause several health issues in humans,including skin cancer and cataracts (clouding of the eye lens).
Therefore,all the listed options are consequences of the ozone hole.

(C) The ozone hole is a region of exceptionally depleted ozone in the stratosphere over the Antarctic.
This phenomenon occurs primarily due to the presence of chlorofluorocarbons $(CFCs)$ and other ozone-depleting substances that react with ozone molecules in the presence of sunlight.
Due to specific atmospheric conditions and polar stratospheric clouds over Antarctica,the depletion is most severe in this region,making the ozone hole largest there.

(B) The thickness of the ozone layer in a column of air from the top of the atmosphere to the ground is measured in terms of Dobson units $(DU)$.
One Dobson unit is equivalent to a $0.01 \ mm$ thickness of pure ozone at a temperature of $0^{\circ}C$ and $1 \ atm$ pressure.
Therefore,the correct option is $B$.

(B) The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of numerous substances that are responsible for ozone depletion.
It was signed in $1987$ in Montreal,Canada,and came into force in $1989$.
This agreement is considered one of the most successful environmental treaties globally.

(B) World Ozone Day is celebrated annually on $16^{th}$ September.
This date was designated by the United Nations General Assembly to commemorate the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in $1987$.
The primary objective of this day is to raise awareness about the depletion of the ozone layer and to find solutions to preserve it.

(B) The thickness of the ozone layer in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units $(DU)$.
One Dobson unit is the thickness of $0.01 \ mm$ of ozone at standard temperature and pressure $(STP)$.
Decibels $(dB)$ are used to measure the intensity of sound,not the thickness of ozone.

(B) The Dobson unit $(DU)$ is the standard unit used to measure the total amount of ozone in a vertical column of air above the Earth's surface.
$1 \ DU$ is defined as $0.01 \ mm$ thickness of ozone at standard temperature and pressure $(STP)$.
Therefore,it measures the thickness of the ozone layer.

(C) The depletion of the ozone layer in the stratosphere allows harmful ultraviolet $(UV)$ radiation to reach the Earth's surface. Prolonged exposure to these $UV$ rays damages the $DNA$ in skin cells,which leads to an increased risk of skin cancer.

(C) Statement $I$ is correct because the absorption of $UV$ radiation by the ozone layer is directly proportional to the concentration or thickness of the ozone layer (measured in Dobson units).
Statement $II$ is incorrect because ozone is generated in the stratosphere by the action of $UV$ radiation (specifically shorter wavelengths) on molecular oxygen $(O_2)$,not by infrared radiation.

(D) The ozone layer in the stratosphere is primarily depleted by Chlorofluorocarbons $(CFCs)$.
$CFCs$ are released into the atmosphere from refrigerators,air conditioners,and aerosol sprays.
In the stratosphere,these compounds are broken down by ultraviolet $(UV)$ radiation,releasing chlorine atoms.
These chlorine atoms act as catalysts in the breakdown of ozone $(O_3)$ into oxygen $(O_2)$,leading to the thinning of the ozone layer.

(C) The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production and consumption of numerous substances that are responsible for ozone depletion.
These substances are primarily Chlorofluorocarbons $(CFCs)$.
It was signed in $1987$ and is considered one of the most successful environmental agreements.