air pollution on buildings

Air pollutants are of major importance for the deterioration of many materials used in cultural monuments. Environmental destructive factors such as severe fluctuations in temperature and moisture and the seasonal changes in these two factors, fire… are not new; they have always existed and have had their destructive effect on the cultural heritage over the years. Relative humidity and air temperature have definite effects on the stability and strength of monuments. Relative humidity of a specific amount of air is defined as the ratio between the amount of moisture in a specific amount of air and the moisture required for saturation of the same amount at the same temperature. Though there are many reasons for degradation the principal reason may be attributed to air pollution. The air pollution in the form of acid rain may be chiefly responsible. The pollutants that are principally responsible for acid rain are sulphur dioxide and nitrogen dioxides. These two are emitted from the combustion of fossils fuels like coal and oil. The rapid industrialization has encouraged the quantity of these emissions. The information on materials damage due to air pollution is very scanty. However, the information on corrosive effects of acid precipitation on metals is available for a few cities.

In fact, all most all materials are affected by the deposition of acid, but the degree of damage or intensity may be varied. Some of them are more susceptible to the affect such are Carbon, Steel, Zinc, Nickel, Limestone, Marble, Paints and some plastics. Basically metallic materials are spoiled due to corrosion. Oxygen and moisture are the chief agents responsible for corrosion. Submerged structures like foundations and pipes will also be affected by acidified waters due to corrosion caused by acid attack.

The damage due to air pollution on materials is really a serious concern since the service life of buildings is remarkably reduced. It is true that the intensity of manmade pollutants on building degradation is more than the impact of natural pollutants. Most importantly the affects of soiling, degradation, corrosion and erosion caused by So2 are very much serious. The effect of air pollution on materials may be seen in terms of discoloration, material loss, structural failing and soiling. Both discoloration and structural failure due to air pollution on buildings may be insignificant and that may not involve huge coasts. But the effect of corrosion due to acidic deposition costs a lot. Especially the effect of sulphur dioxide and nitrogen dioxide emissions is very much significant. The effect of calcium sulphate has been very significant and may be continued for fairly long time. When calcium carbonate dissolves in sulphuric acid leads to the formation of calcium sulphate. The calcium sulphate when it falls on stone breaks the surface of the building blocks.

All most all heritage structures are built up with lime stone and calcareous stones which are most vulnerable to corrosion. Hence continuous renovation and retrofitting is a must to protect our heritage. The historic structures all around the world are affected by acid rain. Most of the studies for the long time focused on the effect of sulphur pollutants, later the interest was diverted to the effect of nitrogen residues on the structures.in fact the effect of acid deposition on material can be studies under two important heads The Taj Mahal, one of the Seven Wonders of the World, and India’s pride, greatest land mark is also being threatened from air and water pollution. Charminar, one of the greatest monuments in India, is being threatened by air pollution.The present contribution showed a general description on the current state of some of the historical structures. In fact the present situation of historical structures is at critical junction. It is necessary that the appropriate governments should initiate substantial measures to control the damage of structures. The awareness among the public is also important to stimulate the concerned authorities to initiate control and remedial measures.