Source

Sulfur compounds present in some fossil fuels burn to form sulfur dioxide. Coal and heavy fuel oils can be important sources if sulfur is not removed.

Acid rain

Sulfur dioxide dissolves and is oxidised in atmospheric water, forming acidic solutions. Acid rain damages vegetation, aquatic systems and carbonate stone and can accelerate metal corrosion.

Low-sulfur fuels

Using fuels with less sulfur reduces SO2 at source. Shifting away from sulfur-containing fossil fuels has broader air-quality benefits.

Flue-gas desulfurisation

Basic calcium oxide reacts with acidic sulfur dioxide in exhaust gases, forming a calcium sulfur compound that can be removed as a solid. This prevents much SO2 reaching the atmosphere.

High-value recall and connections

Essential recall: What is the main source of SO2? Combustion of fossil fuels containing sulfur compounds. What environmental problem does it cause? Acid rain. How can flue gases be treated? React them with calcium oxide to remove SO2. Practical connection: Given SO2 emission data before and after treatment, calculate percentage removal and evaluate whether a legal target is met. Examination connection: Calcium oxide is used because it is a basic oxide that reacts with acidic sulfur dioxide.

Review questions and suggested answers