Explanation

Acid rain and smog are example of regional pollution. Acid rain is caused mainly by oxides of sulphur and nitrogen and has a pH of 4 or 4.5. once in the air these oxides may react with moisture to form $H_{2}SO_{4}$ and $HNO_{3}$. $SO_{2}\ \$(oxidized) $\longrightarrow SO_{3} + H_{2}O$ $\longrightarrow$ $H_{2}SO_{4}$ $NO$(oxidized) $\longrightarrow$ $NO_{2} + H_{2}O\ \longrightarrow$ $HNO_{3}$ Smog is harmful mixture of smoke and fog. It consists of mixture of primary and secondary pollutants ($eg.$ Hydrocarbons, $NO_{2},$ PAN,$HCHO$).