Acid rain is created by air pollutants. Sulphur dioxide, a byproduct of industrial development and burning fossil fuels, combines with nitrogen oxide, an air pollutant created by car exhaust, furnaces, boilers and engines. The chemicals fall to earth as acid rain. Of all the building stones, granite is the least susceptible to acid rain because its composition is of feldspar and quartz, both of which resist attacks of acid. However the acid found in rain, snow, fog and dust is beginning to affect some granite buildings and statues, granite lake beds and the wildlife they contain.
Most buildings in the city of Oporto, Portugal, are built of Oporto granite, found in veins throughout the nearby Duoro Valley. The city is known for its high pollution levels, the salt air blowing in from the Atlantic Ocean and its acid rain. Oporto granite is beginning to show effects from acid rain, as many historical buildings and statues in the city are beginning to deteriorate. Some of the destruction is also caused by Portland cement, used for repairs to the granite buildings and monuments. The acid rain deteriorates the cement and adjacent seams become pooling areas. Adjacent granite is also affected.
Rio de Janeiro
Granite is the stone most prominently used in the construction of buildings in Rio de Janeiro. Intense pollution creates a thin black crust on the facades of stone buildings, including those made of granite. The highly trafficked area and canyon-like placement of buildings, plus the salty winds coming in from the sea and the acid rain combine to intensify the weathering of some of the most prominent buildings in the city.
Granite is often used for tombstones in the United States. The position of the stone within the graveyard directly affects its deterioration. Heat from the sun, biological growth around the tombstone, high winds, the tombstone's design and acid rain factor in the deterioration process. Deterioration is more prevalent in coarse-grained granites that are roughly polished. The dips and crevasses harbor trapped pollutants. The longer the acid rain sits on the granite, the more quickly it deteriorates the stone.
Granite in the Earth’s Structure
When beds of freshwater lakes are made of soils and rocks containing calcium and magnesium, the acid rain is neutralized and a healthy alkaline level is maintained. The water and its inhabitants are untouched by the effects of the acid rain. Granite, with its quartz and feldspar composition, forms much of the Earth's structure in the northeast United States and Canada. Many lakes surrounded by granite rock maintain a high acidic level because the granite does not neutralize the acid, and the low alkaline levels contribute to the killing of fish and living organisms.
- Internet Archive; Granite Deterioration in the Graveyard of Saint James the Less, Philadelphia; Kathryn Marit Sather; 1990
- Elmhurst College; Acid Lakes; Charles Ophardt; 2003
- Environment Canada: Acid Rain and the Facts
- United States Geological Survey; Weather Science for Schools; Acid Rain
- Annals of the Brazilian Academy of Sciences; Surface Modification of a Granite Building Stone in Central Rio de Janeiro; Batisto-Neto, Smith et al; July 22, 2004
- University of Minho; Granite Weathering and Stone Deterioration in Monuments and Buildings in Oporto; Arlindo Begonha; 1997
- National Atmospheric Deposition Program: Acid Rain
Jann Seal is published in magazines throughout the country and is noted for her design and decor articles and celebrity *in-home* interviews. An English degree from the University of Maryland and extensive travels and relocations to other countries have added to her decorating insight.