write:pollutant effects on building surfaces are very evident. Soiling and staining of buildings in urban areas that have or have had high atmospheric aerosol levels is a particularly st

pollutant effects on building surfaces are very evident. Soiling and staining of buildings in urban areas that have or have had high atmospheric aerosol levels is a particularly striking example. The “dirtiness” associated with many cities is due to the dark coating of particulate dusts deposited by the smoke of industries and coal-fired space heating over many years. In addition to soiling
building materials such as marble
limestone
and carbonate cement are chemically eroded by SO2 and acid aerosols. The reaction of SO2 with carbonate building stones results in the formation of hydrated Ca salts
CaSO3·2 H2O and CaSO4·2 H2O (gypsum)
both of which are H2O soluble. The soluble salts produced may precipitate from solution and form encrustations; as they are washed away
the stone surface becomes more susceptible to pollutant effects. Stone damage is further accelerated by sulfur (S)-oxidizing bacteria and fungi. Deterioration rates are affected by pollutant concentration
moisture content and permeability of stone
and deposition rates. Dry deposition of SO2 between rain events has been reported as the major causal factor in carbonate building stone deterioration. Pollutant-induced erosion on a carbonate stone street monument can be seen in Figure 6.6. Chemical erosion of priceless
irreplaceable historical monuments and works of art in western and southern Europe can be described as no less than catastrophic. Although primarily a European problem
similar destruction is occurring on monuments in the U.S. In the late 19th century
the obelisk
Cleopatra’s Needle
was moved from Egypt to a park in New York City. The monument
which had withstood the ravages of desert heat and sands for thousands of years without significant deterioration
has had hieroglyphics obliterated on two of its faces in the past half century. The other two faces have eroded less
as they were away from the direction of prevailing winds. A significant concern is the Acropolis
located downwind of Athens
Greece. Although chemical erosion of marble structures in the Acropolis has been occurring for more than 100 years
rapid population growth and use of high-S heating oils since World War II have greatly accelerated their destruction. In addition to the Acropolis
the Colosseum in Rome and Taj Mahal in India are in various stages of dissolution. In many European cities
marble statues have had to be moved indoors. Cities such as Venice have enacted legislation to preserve and restore hundreds of damaged piazzi
churches
and historical buildings. The grand cathedrals of Europe (e.g.
Notre Dame
Chartes
and Cologne) are constantly Welfare effects 221