In industrial cities with heavy flue gas emissions, the atmosphere contains significant concentrations of sulfur dioxide (SO₂) and solid particulates. These particulates consist of 30% insoluble residue, 33% combustion residue from burned fuels, 20% iron oxides, and 8% water-soluble sulfates. When sulfur dioxide dissolves in rainwater, it forms strongly acidic solutions that aggressively corrode zinc coatings. Even if a protective layer of zinc oxide, zinc hydroxide, and zinc carbonate has formed on the zinc surface, this layer can dissolve into soluble zinc sulfate under the acidic aqueous conditions, leading to accelerated corrosion. Consequently, the corrosion rate of zinc coatings exhibits a nearly direct proportionality to the SO₂ concentration in the atmosphere.
Solid particulates also contribute to localized corrosion of zinc surfaces. Some particulates exhibit hygroscopic properties, absorbing moisture and dissolving sulfur compounds to form acidic solutions. These localized acidic environments induce selective corrosion at the contact points. The typical corrosion rate of zinc coatings in sulfur-containing industrial atmospheres ranges from 420 to 770 mg/dm²·year.
