How does sulfur dioxide cause air pollution?

Sulfur dioxide (SO2) results from the combustion of fuels containing sulfur or sulfurous chemicals, the combustion of H2S in flares, paper production, and the smelting of ores containing sulfides.

SO2 exhausted to the atmosphere may cause respiratory problems in sensitive individuals such as asthmatics. It can also cause damage to plants and trees, such as the reddening of pine needles. It can hasten the corrosion of iron and other metals.

If the SO2 combines with water vapour, it can cause acid precipitation which can erode metal and limestone, impact the ionic balance of clay soils, fade paints and change the pH of river and lake water to the detriment of fish and other aquatic organisms.

In all of these cased the impact of atmospheric SO2 is to combine with water in plant ot animal cells, atmospheric water, or standing water to make sulfurous acid (H2SO3). If the SO2 oxidizes in the atmosphere to sulfur trioxide (SO3) it can combine with water to form sulfuric acid (H2SO4) with stronger environmental chemical reactions.