• # question_answer 7) Write down the reactions involved during the formation of photochemical smog.

Sunlight causes photochemical decomposition of$N{{O}_{3}}$. $N{{O}_{2}}+hv\to NO+O$ Atomic oxygen combines with molecular oxygen to form ozone. ${{O}_{2}}+O+M\to {{O}_{3}}+M$ M is an inert gas such as nitrogen. It takes up the excess energy. Ozone attacks the unsaturated hydrocarbon. A second process involving hydrocarbons may be depicted as: $N{{O}_{2}}+hv\to NO+O$ $O+RH\to \overset{\centerdot }{\mathop{R}}\,+RC\overset{\centerdot }{\mathop{O}}\,$ $RC\overset{\centerdot }{\mathop{O}}\,+{{O}_{2}}\to RC{{\overset{\centerdot }{\mathop{O}}\,}_{3}}$ $RC\overset{\centerdot }{\mathop{{{O}_{3}}}}\,+N{{O}_{2}}\to RC{{O}_{3}}N{{O}_{2}}$ (Peroxyacetyl nitrate, PAN) The oxidation of hydrocarbons produces various organic intermediates which are less volatile. These substances condense into small droplets of liquid. The aspersion of these droplets in air forms smog. This reduces visibility and looks hazy.