Atmospheric corrosion is an important impact of air pollution damaging cultural heritage and other man-made materials and resulting in large economic losses. The corrosion is due to a combination of the action of a number of pollutants interacting with meteorological parameters. The damage can be caused by wet deposition of acidic rain, dry deposition of gases such as sulphur dioxide and particulate deposition. The impacts of corrosion are felt mainly in urban and marine settings and in urban areas are particularly related to the concentrations of pollutants such as sulphur dioxide.

These impacts have occurred widely in Europe and this has been particularly clear on cultural monuments where many have been destroyed over the last one hundred years, even if they survived the previous three hundred. Pollution damage to cultural monuments is of concern in developing countries where impacts are now being felt, especially as there is evidence that corrosion at a given level of pollution proceeds more rapidly under warm humid conditions. In Europe high costs of pollution related corrosion have been calculated for the maintenance of deteriorating buildings and cars in the urban environment.

Against this background the Malé Declaration set out to establish dose-response relationships for the tropical and sub-tropical regions of South Asia, working in collaboration with the RAPIDC Corrosion Network (CORNET) with site across the whole of Asia and in Southern Africa. CORNET put the information together to derive dose-response relationships for various materials under Asian and African conditions, which are a pre-requisite for economic loss assessments.

Malé Declaration achievements and results

  • The capacity to understand the air pollution impacts of corrosion on materials and cultural heritage has been significantly increased in South Asia, as well as the capacity to undertake stock at risk and economic loss assessments.
  • The most important pollution parameters have been shown to be the same in subtropical/ tropical climates as in temperate climates, but the relative importance of the effects as well as the influence of climate can still be different.
  • New dose-response functions have been developed for carbon steel, zinc, copper and limestone for South Asian conditions.
  • In South Asia, dry deposition of sulphur dioxide (SO2) is the most important parameter for corrosion impacts but acid rain is also important for all materials while nitric acid (HNO3) is important for the corrosion of zinc and limestone.
  • Using results from the Malé Declaration a tolerable SO2 level for materials including cultural heritage in the Kathmandu Valley of 6 μg m-3 has been proposed.
  •  A Regional Centre of Corrosion Impact Assessment is currently being established in India to oversee coordination, harmonization, quality control and reporting of the Malé Declaration corrosion impact activities.

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