Atmospheric corrosion effects of air pollution on materials and cultural property in Kathmandu, Nepal

摘要

Ten racks with materials (carbon steel, zinc and limestone) and passive samplers for pollutants (gaseous SO_2, NO_2, O_3 and HNO3 as well as particulate matter, total mass and ions), were exposed in the Kathmandu area for one year. The results show that the rates of corrosion for iron, zinc and limestone vary considerably across the Kathmandu valley and are correlated mainly with the SO_2 concentration. The data range from 2 - 20 μg m~(-3) (SO_2), with 5 - 13 μm year~(-1) (limestone recession), 5 – 60 μm year-1 (carbon steel corrosion) and 0,4 – 1,1 μm year~(-1) (zinc corrosion). It was possible to obtain a tolerable SO_2 concentration for protection of cultural heritage of 5-6 μg m~(-3) (for carbon steel, Figure 1, below) and 6-7 μg m~(-3) (for limestone) for the Kathmandu valley based on this these data.rnThe paper also presents an overview of corrosion results from exposures of carbon steel, zinc, copper, limestone and paint coated steel where corrosion attack after one, two and four years of exposure was obtained from more than twenty test sites in Asia and Africa. These results obtained within the Swedish Sida funded Programme on Regional Air Pollution in Developing Countries (RAPIDC) also identify SO_2 as the main pollutant but HNO3 is also important for zinc and limestone as is also the case for samples exposed in Europe. Absolute corrosion rates are also similar in magnitude compared to Europe with the exception of some individual sites in Asia/Africa with very high pollution levels. For some materials, especially for limestone, there is also generally higher degradation levels in Asia/Africa compared to Europe.