What type of air pollution causes corrosion of iron / steel?
Unprotected iron and steel will corrode in a pollution-free humid atmosphere. The man-made pollutant that contributes the most to corrosion of iron and steel is sulfur dioxide, which combines with water in the atmosphere to form weak sulfuric acid, or “acid rain”. Salt will accelerate corrosion, so any atmmospheric source of chlorides, natural or man-made, will contribute. In general, any pollutant that lowers the pH of rainwater will accelerate corrosion.
