Oxidation of sulphur dioxide into sulphur trioxide in the absence of a catalyst is a slow process but this oxidation occurs easily in the atmosphere. Explain how does this happen? Give chemical reactions for the conversion of `SO_(2)` into `SO_(3)`.

Explanation

The oxidation of sulphur dioxide into sulphur trioxide can occur both photochemcally or non-photochemially. In the near ultraviolet region, the `SO_(2)` molecules react with ozone photochemically.
`SO_(2) + O_(3) overset(hv) rarr SO_(3) + O_(2)`
`2SO_(2) + O_(2) overset(hv)rarr 2SO_(3)`
Non-photochemically, `SO_(2)` may be oxidised by molecular oxygen in presence of dust and soot particles.
`2SO_(2) + O_(2) overset("Pariculates")rarr 2SO_(3)`