Corrosion of materials

The effects of wind and weather naturally mean that all materials will decay sooner or later, but air pollution speeds up this process.

Corrosion means damage of buildings, vehicles, metal structures, statues, rock carvings, museum artefacts, water pipes, electrical cables etc., caused by acidifying substances. Objects made of limestone and some types of sandstone are especially vulnerable to acid substances, but not even the hardest granite can resist entirely.  

The greatest damage is caused by sulphur dioxide, which is corrosive in both gaseous form and when converted into sulphuric acid. Nitrogen oxides also contribute to the damage, partly through the formation of corrosive nitric acid, and partly by reinforcing the damaging effects of sulphur dioxide. Ozone and other oxidants react readily with organic substances. They contribute mainly to the breakdown of textiles, leather and rubber. As a result of its oxidizing ability ozone can also increase the corrosiveness of compounds of sulphur and nitrogen oxides.

Dry fallout is considered to do more damage than wet, since it can dissolve in the film of condensation on various surfaces and remain there for a long time. This can lead to
high concentrations that are highly corrosive, since the pollutant is dissolved in such a small quantity of water. It also means that the pollutant can be “reused" as long as it remains there. It may dry out in the meantime, but can go back into solution whenever the surface becomes moist, with dew for example. Rain on the other hand, even if it is acidic, washes the pollutants away.

Source: Air and the environmentexternal link, opens in new window by P.Elvingson and C.Ågren

Updated: 2012-10-16
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