Question

From where does ozone come in the photochemical smog?

Answer 1

Photochemical smog is a brownish-grey haze. It is caused by the action of solar ultraviolet radiation on an atmosphere polluted with hydrocarbons and oxide of nitrogen.

Sunlight causes the decomposition of $N{O}_2$ into 𝑁𝑂 and nascent oxygen.

$N{O}_2\stackrel{hv}{\to }NO+\left[O\right]$

𝐴𝑡𝑜𝑚𝑖𝑐 𝑜𝑥𝑦𝑔𝑒𝑛 (𝐻𝑖𝑔ℎ𝑙𝑦 𝑟𝑒𝑎𝑐𝑡𝑖𝑣𝑒 𝑠𝑝𝑒𝑐𝑖𝑒𝑠)

When atomic oxygen combines with an oxygen molecule, it forms ozone.

$O_2+\left[O\right]\to O_3$

Hence, this ozone $\left(O_3\right)$ is formed during the formation of smog.