Write down the chemical equations of reaction involved during the formation of photochemical smog?How can it be controlled?

Control: (i) Efficient catalytic converters are being developed for fitting in the automobiles so that the emission of nitrogen oxides and hydrocarbons can be prevented.
(ii) Certain chemical compounds are sprayed into
atmopshere, which generate free radicals. These free radicals readily react with the free radicals responsible for the formation of photochemical smog and nullify their effect.
(iii) Toxic nature causes coughing, wheezing, bronchial constrictions and irritation to respiratory mucous system.