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.
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