When fuels containing sulfur are burned, the sulfur atoms are oxidised. They react with oxygen in the air to form sulfur dioxide gas:
Sulfur + Oxygen → Sulfur dioxide
S + O2 → SO2
In the atmosphere, sulfur dioxide can undergo further oxidation to form sulfur trioxide gas. This gas dissolves in rainwater to form acid rain, producing sulfuric acid (H2SO4). The process involves two reactions:
1. Sulfur dioxide + Oxygen → Sulfur trioxide
2SO2 + O2 → 2SO3
2. Sulfur trioxide + Water → Sulfuric acid
SO3 + H2O → H2SO4
Acid rain is a type of rain that has a high level of dissolved acidic compounds in it. There are many problems associated with acid rain, including:
Oxides of nitrogen are pollutants typically produced inside vehicle engines and then released. For example, the high temperatures in cars cause nitrogen to react with oxygen in the air to produce a range of molecules. We call these molecules oxides of nitrogen or NOx.
Nitrogen + Oxygen → Oxides of Nitrogen
N2 + O2 → NOx
NOx gases react with other pollutants in the atmosphere to form photochemical smog, which can affect the health of individuals, especially those suffering from asthma.
Both sulfur dioxide and oxides of nitrogen contribute to acid rain.