Question

What emissions from human activities lead to ozone depletion? And what are the principle steps in stratospheric ozone depletion caused by human activities?

Answer 1

Human activities cause the emission of halogen source gases that contain chlorine and bromine atoms. These emissions into the atmosphere ultimately lead to depletion of the ozone layer. The source gases that contain only carbon, chlorine, and fluorine are called chlorofluorocarbons.

Complete step by step answer:
Certain industrial processes and consumer products result in the atmospheric emission of “Halogen source gases”. These gases contain chlorine and bromine atoms, which are known to be harmful to the ozone layer. For example, the chlorofluorocarbons $\left( {CFCs} \right)$ and Hydrochlorofluorocarbons $\left( {HCFCs} \right)$,once used in almost all refrigeration and air condition systems, eventually reach the stratosphere where they are broken apart to release ozone-depleting chlorine atoms.
Other examples of human-produced ozone-depleting gases include the “Halons”, which are used in fire extinguishers and which contain ozone-depleting bromine atoms.
The production and consumption of all principal halogen source gases by human activities are regulated worldwide under the Montreal protocol.
The principle steps in stratospheric ozone depletion caused by human activities include:-
-Emissions – Halogen source and other ozone depleting gases are emitted at earth’s surface by human activities and natural processes.
-Accumulation – This gases which do not react gets accumulated in the lower atmosphere.
-Transport – Through air movements these gases are then transported to the stratosphere.
-Conversion – In the stratosphere the gases then react and convert into more reactive harmful ultraviolet radiations.
-Chemical reactions – The reactive halogen gases cause chemical depletion of the ozone layer.

Additional Information: A variety of gases transport chlorine and bromine into the stratosphere. These gases, called halogen source gases, are emitted from natural sources and human activities for chlorine, human activities account for most of the percentage that reaches the stratosphere.
The $CFCs$ are the most abundant of the chlorine-containing gases released by human activities. Eg, Methyl chlorine. For bromine that reaches the stratosphere halons and methyl bromide are the largest sources. Both gases are released by human activities.

Note: Other gases that influence stratosphere ozone abundance also have increased in the stratosphere as a result of human activities. Important examples are methane $\left( {C{H_4}} \right)$ and nitrous oxide $N_{2}O$ which react to form water vapours and reactive hydrogen and nitrogen oxides, respectively, in the stratosphere.