Impact of air pollutants on some building materials in Cairo atmosphere

Gaseous and particulate air pollutants are significantly affect non-biological materials. Of particular importance are effects on building stones, historic and cultural monuments, which create an important part of our cultural heritage.1–3 The effect of the deposition of atmospheric gases and aerosols on building materials constitutes one of the main damage mechanisms threatening the cultural heritage. Physical changes and chemical interaction occur at the building surface when exposed to outdoor atmosphere. The action of chemicals usually results in irreversible changes. Consequently, chemical damage to materials is of more serious problem.3,4 Dry deposition of gases plays an important role for the deterioration of stone materials. The dry deposition of gaseous air pollutants on stone and other materials is influenced by atmospheric processes and the chemical characteristics of the deposited gas species and of the specific receptor materials.5–7 The absorbed gases may act directly on the material, or first be converted to new substances that are responsible for observed effects. Gaseous pollutants such as sulfur dioxide and nitrogen oxides can react directly with the stone surface by forming acids in the presence of water (or moisture) and oxidizing agents. The formed acids react with the stone to form salts which either crystallize out within the stonework resulting in physical damage or they are washed away resulting in a loss of material.8–10 Sulfurous or sulfuric acids are capable of attacking a wide variety of building materials, including limestone, sandstone, concrete, marble, roofing slate, mortar, etc. Fairly soluble sulfates are formed, which are then leached away by rain.11,12 In Egypt, which is a repository for many buildings of history, museums and monuments, no previously serious study on air pollutants-induced damage on building materials could be traced. The cultural treasures are irreplaceable, so their preservation from the destructive effects of airborne contaminants poses a significant challenge to their present conservators. The aim of this work is to identify the environmental damage caused to some building materials by air pollutants in Cairo atmosphere and to assess to which extent urban and industrial atmosphere affect and accelerate the “natural” corrosion of materials. The study of environmental damage on stones and building materials is of fundamental importance in both the preservation of modern buildings and corrects planning of conservation works on historical monuments, in which such materials are commonly used.