Q.How is SO2 an air pollutant?

Step 1: Source of atmospheric $SO_2$.

Combustion of sulphur-containing fossil fuels (coal, petroleum) in power plants, vehicles and industries, as well as smelting of sulphide ores, releases large quantities of $SO_2$ into the atmosphere.

Step 2: Direct toxic/irritant effect.

$SO_2$ is a toxic gas that irritates the respiratory tract (eyes, nose, throat, lungs) even at fairly low concentrations, aggravating asthma and other respiratory conditions in humans, and damaging plant tissue directly.

Step 3: Acid rain formation.

In the presence of moisture and atmospheric oxidants, $SO_2$ is oxidised and hydrated to sulphurous and sulphuric acid:

$SO_2 + H_2O \rightarrow H_2SO_3$ …

State SO2's main emission source (burning fossil fuels/smelting), its direct toxic/irritant effect on health, and its indirect role via atmosph …

• Do not describe only the acid-rain angle and omit SO₂'s direct respiratory toxicity, or vice versa — both aspects together answer "how is SO₂ an air pollutant."
• Acid rain is caused by conversion of SO₂ to H₂SO₄/H₂SO₃ in the atmosphere, not by SO₂ gas itself falling as rain — the oxidation/hydration step must be shown. …