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

Sulphur dioxide `(SO_(2))` is normally oxidised to sulphur trioxide `(SO_(3))` in the presence of a catalyst. However, particulate matter present in the atmosphere promotes the oxidation of sulphur dioxide. Even ozone layer in the atmosphere causes the oxidation.
`SO_(2)(g)+O_(3)(g)rightarrowSO_(3)(g)+O_(2)(g)`