SO2 also reacts with water to form acid rain, so the lower the SO2 the less acid rain which is good for building, limestones, rocks etc.
The sulfur in petrol and diesel is oxidised during combustion to sulfur dioxide.
S
8 + 8 O
2 --> 8 SO
2
The sulfur dioxide enters the atmosphere where it is oxidised by the hydroxyl radical and then by oxygen to sulfur trioxide.
SO
2 + OH
. --> HOSO
2.
HOSO
2. + O
2 --> HO
2. + SO
3
The sulfur trioxide reacts with water vapour forming sulfuric acid.
SO
3 + H
2O --> H
2SO
4
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Dilute sulfuric acid attacks iron, aluminium, zinc, manganese and nickel metals to release metal ions. Aluminium has no known biological role and considered a neurotoxin.
The acid reduces the pH of surface water. At a pH less than 5 most fish eggs do not hatch and fish and other animals are killed.
Acid leaches essential nutrients out of soil. For example magnesium ions locked in clay are leached and washed away.
Acid reacts with calcium carbonate in limestone, sandstone, marble and granite to produce calcium sulfate which gets washed away.
CaCO
3 + H
2SO
4 --> CaSO
4 + CO
2 + H
2O
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Sulfate aerosols contribute to reduced visibility in cities due to the presence of smog, and in volcanic regions due to vog.