Effects of air pollutants on buildings and materials

Abstract

SynopsisThe main pollutants affecting materials are sulphur dioxide and sulphates, nitrogen oxides and nitrates, chlorides, carbon dioxide and ozone. In marine environments it is important to separate the effects of anthropogenic pollutants from marine sources of the same substances. The effects of paniculate matter, especially from diesel vehicle emissions is of increasing significance.In buildings containing books, historical artefacts or other works of art indoor pollutants may cause significant degradation. These pollutants may either be lower concentrations of pollutants originating outdoors or other substances generated from synthetic materials, paints, varnishes and display cases as well as from combustion for heating.The materials most sensitive to pollutants are calcareous building stones and ferrous metals. Manifestations of damage include losses of mass, changes in porosity, discoloration and embrittlement. In the case of stone it is difficult to (1) dissociate the effects of historical concentrations of pollution from current ones and (2) to establish background rates of erosion or decay in the absence of pollutants.Damage to materials in polluted atmospheres can be attributed to dry or wet deposition of pollutants, or dissolution in rainfall in the case of stone. Estimates of the contributions of the different mechanisms of decay have been made in programmes in the U.S.A. and the U.K.To obtain estimates of the economic cost of damage from acid deposition it is necessary to know how decay rates are related quantitatively to pollutants and meteorological parameters (damage functions), and the distribution of materials exposed in buildings and in geographical areas. There are few damage functions available and those in existence lack general applicability. There is. therefore, much importance attached to national and international exposure programmes that have been established to assess the responses of a range of materials to different environments. Such work is also of interest in predicting the potential effects of climatic changes on materials.Methodologies have been developed to enable estimates of economic costs of damage to be made. These are being refined with better data on rates of decay obtained from mathematical models and from exposure programmes. The concept of target loads for damage, originally devised for the natural environment, is being introduced to help assess the action needed to reduce degradation of sensitive materials and buildings.