Fill in the blanks in the equations and statements below.

Sulphur dioxide (a pollutant) is oxidised in the atmosphere to sulphur trioxide (a pollutant) which then reacts with water to form sulphuric acid.

The oxidation of sulphur dioxide can occur in various ways

1. Reaction in water droplets

SO₂(g) + (l)  -->  HSO₃^-(aq) + H⁺(aq)

HSO₃^-(aq) + ¹/₂(aq) -->  HSO₄^-(aq)

This process is slow but is catalysed by ions, such as manganese(II) found in atmospheric aerosols.

2. Photochemical reaction

SO₂ +  -->  SO₂*   where * denotes an electronically excited species

SO₂* +  -->  SO₃ + O

3. Gas phase reaction with ozone

SO₂ + O₃  --> + O₂