Environmental and Economic Impacts:

Ancient Monuments

 

 

 

 

Acid deposition has been slowly eating away at Egypt’s monuments which are significant not only culturally, but also economically since they are an

important component of Cairo’s tourism industry.

 

 

The exteriors of the ancient monuments are made mostly of limestone which is particularly susceptible to damage from acid deposition.  Limestone consists of calcium carbonates (CaCO3) that, when exposed to sulfuric acid, dissolve into aqueous ions (7) and wash away with the rain. The chemical reaction is as follows(8):

 

 

 

 

 

 Erosion of the exterior surface thus ensues, and results in the destruction of

 important architectural details of the monuments while usually keeping the structural integrity of the monuments intact.

 

 

 Additional damage continues to occur when the calcium and sulfate ions that are left behind crystallize in the form of gypsum (9). When gypsum is not washed away by subsequent rainfall, which is not likely to occur in Cairo’s

desert climate, it will attract various pollutants such as carbonic aerosols, dust, and ash resulting in the blackening of the stone’s surface. When the gypsum eventually falls off, it removes yet even more of the underlying surface.  In fact, the gypsum crystals can sometimes grow into the vesicles of the porous limestone where the slow process of erosion can continue for up to 50 years. This is known as the Memory Effect (10).

 

 

 Pollutants that are left on the surface, either through this process or through dry deposition, maintain harmful potentials that are dependent upon the amount of moisture present in the environment.  The ancient monuments are particularly   prone to such damage since humidity levels of the tombs are often raised by several percentage points due to the large number of visiting tourists (11).