Question

Name the gases that are harmful to the Ozone layer.

Answer 1

Hint: The ozone layer has high concentration of $O_3$ (ozone) as compared to other parts of the atmosphere and it is that region of Earth's stratosphere which absorbs most of the Sun's ultraviolet (UV) radiations. The quantity of ozone $O_3$ is still small in comparison to other gases in the stratosphere. The absorption of ultraviolet light of Sun ( which has a wavelength of about 200nm to 315 nm) by the ozone layer is around 97 to 99 percent, if this uv light did not absorb by ozone then it has the potential to damage exposed life forms near the surface of earth.

Complete answer:
The ozone layer thickness varies from place to place, as it is generally thinner near the equator and thicker near the poles. The thickness of the layer tells us how much ozone is in a column over a given area and this thickness varies from season to season. The reasons for variations in thickness is due to solar intensity and atmospheric circulation patterns.
Majority of the ozone $O_3$ is produced over the tropics and is transported towards the poles with the help of stratospheric wind patterns.
The depletion of the ozone layer can be caused by free radical catalysts, including nitrous oxide ($N_2O$), nitric oxide (NO), hydroxyl (OH), atomic bromine (Br), and atomic chlorine (Cl). While there are natural sources for all of these gases but the concentrations of chlorine and bromine increased markedly in recent decades because of the release of large quantities of chlorofluorocarbons (CFCs) and bromofluorocarbons (BFCs), these are man-made organohalogen compounds.
The CFCs and BFCs compounds are highly stable in the environment and are capable of surviving the rise to the stratosphere, where Cl and Br radicals are liberated by the action of ultraviolet (UV) light. Each free radical is able to initiate and catalyze a chain of reactions and is capable of breaking down over 100,000 ozone molecules. In the year 2009, it was found that nitrous oxide was the largest ozone-depleting substance (ODS) emitted by human activities into the atmosphere.
The breakdown of ozone in the stratosphere results in reduced absorption of ultraviolet radiation which causes unabsorbed and dangerous ultraviolet radiation to reach the Earth's surface at a higher intensity.

Note:
There are various concerns of increased UV radiation due to ozone depletion which threatens life on Earth, this includes various diseases such as increased cases of skin cancer in humans and other ecological problems. If the ban has been imposed on the chemicals, the latest evidence shows that ozone depletion has slowed or stopped.