What is acid rain? Explain the formation of acid rain by atmospheric pollutants.

(N/A) Normally,rain water has a $pH$ of $5.6$ due to the presence of $H^{+}$ ions formed by the reaction of rain water with atmospheric $CO_{2}$:
$H_{2}O_{(l)} + CO_{2_{(g)}} \rightleftharpoons H_{2}CO_{3_{(aq)}}$
$H_{2}CO_{3_{(aq)}} \rightleftharpoons H^{+}_{(aq)} + HCO_{3_{(aq)}}^{-}$
When the $pH$ of rain water drops below $5.6$,it is called acid rain. Acid rain refers to the process by which acidic components from the atmosphere are deposited on the earth's surface.
Acid rain is primarily caused by the emission of sulphur dioxide $(SO_{2})$ and nitrogen oxides $(NO_{x})$ from the burning of fossil fuels (coal,oil,petrol,diesel) in power stations,furnaces,and motor engines.
These oxides react with water in the atmosphere in the presence of particulate matter (which acts as a catalyst) to form strong acids:
$2SO_{2_{(g)}} + O_{2_{(g)}} + 2H_{2}O_{(l)} \rightarrow 2H_{2}SO_{4_{(aq)}}$
$4NO_{2_{(g)}} + O_{2_{(g)}} + 2H_{2}O_{(l)} \rightarrow 4HNO_{3_{(aq)}}$
These acids are deposited on the earth's surface as wet deposition (rain,fog,snow) or dry deposition (solid particles/gases).