effects on stone monuments - University of the Western Cape
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---4 .*..* Pollutant effects on stone monuments The outcome can be predicted with reasonable certainty K. La1 Cauri C. C. Holdren, Jr. University of Louisoille Louisville, Ky. 40292 An oil refinery is being built nearly 30 km upwind from the Taj Mahal in Agra, India. This refinery is expected to emit 25-30 tons of sulfur dioxide daily, which is likely to travel towards the Taj Mahal from October to March due to the prevailing northwesterly winds (I). Such SO2 emissions are expected to corrode the marble at the Taj Mahal in the same fashion that air pollution has contributed to the cor- rosion of marble at the nearly 70- year-old Field Museum of Natural History in Chicago. Fcorrrrc arrirlu.7 in ES&T hoc< hy-linrr. wp rcvm rhr ciuw offhe ovrhorr. ond ore vdirrd h? rhu Worhinpron .sra// If?.ou ore iiirmwed in wnrrihurin~ m arricle. omrocI rhr nmnopinx rdin,,. In December 1978, the senior (first) author of this paper collected a few marble samples at the Taj Mahal to compare their condition with the marbles exposed at the Field Museum of Natural History in Chicagoand the Erechtheion at the Acropolis in Ath- ens. Knowledge of the mechanisms of marble decay enables the conclusion that the marble at the Taj Mahal-in the wake of the effluents of industrial combustion expected to pervade the environment of Agra-shall meet the same fate as the monuments of antiq- uity in industrial Europe and North America. Of constituents produced by the combustion of fossil fuels, NO, and SO2 are the most potent for stone decay. During periods of dryness, they accumulate as particulate matter on stone surfaces and are activated by subsequent wetness. Dissolved in pre- cipitation. they descend as acid solu- tions. In the eastern US.. the acidity of precipitation has achieved a regional pH value below four (2). In the Los Angeles Basin, similar pH values exist due to acid nitrates (3). Emissions rising from stationary sources are commonly deposited at considerable distances from their sources. The pollutants generated in the Ohio Valley (4), for instance. have significantly contributed to the acidity of precipitation in the northeastern US., just as Scandanavian precipita- tion has become contaminated with the emission effluents of Western Europe in the wake of prevailing westerly winds (5). Precipitation in equilibrium with atmospheric COz, the natural cause of acidity, has a pH of 5.65. The weak carbonic acid (H2CO3) that forms by the dissolution of C02 in water has been, until recently, the major cause of marble decay. NO, and SO2 emis- sions, however, have increased the acidity of precipitation. The black crusts and crumbling stone on marble structures in industrialized regions are composed of calcium sulfate, nitrates, and organic particles. Some repre- sentative reactions of these emissions with the marble’s calcite (CaCO3) 380 Environmental Science 8 Technology 0013-936X/81/0915-0386$01.25/0 @ 1981 American Chemical Society
Transcript of effects on stone monuments - University of the Western Cape
---4 .*..*
Pollutant effects on stone monuments The outcome can be predicted with reasonable certainty
K. La1 Cauri C. C . Holdren, Jr.
University of Louisoille Louisville, Ky. 40292
An oil refinery is being built nearly 30 km upwind from the Taj Mahal in Agra, India. This refinery is expected to emit 25-30 tons of sulfur dioxide daily, which is likely to travel towards the Taj Mahal from October to March due to the prevailing northwesterly winds ( I ) . Such SO2 emissions are expected to corrode the marble a t the Taj Mahal in the same fashion that air pollution has contributed to the cor- rosion of marble at the nearly 70- year-old Field Museum of Natural History in Chicago.
Fcorrrrc arrirlu.7 in ES&T hoc< hy-linrr. w p r c v m rhr c i u w offhe ovrhorr. ond ore vdirrd h? rhu Worhinpron .sra// If?.ou ore iiirmwed in w n r r i h u r i n ~ m arricle. omrocI rhr nmnopinx rdin,,.
In December 1978, the senior (first) author of this paper collected a few marble samples a t the Taj Mahal to compare their condition with the marbles exposed at the Field Museum of Natural History in Chicagoand the Erechtheion at the Acropolis in Ath- ens. Knowledge of the mechanisms of marble decay enables the conclusion that the marble a t the Taj Mahal-in the wake of the effluents of industrial combustion expected to pervade the environment of Agra-shall meet the same fate as the monuments of antiq- uity in industrial Europe and North America.
Of constituents produced by the combustion of fossil fuels, NO, and SO2 are the most potent for stone decay. During periods of dryness, they accumulate as particulate matter on stone surfaces and are activated by subsequent wetness. Dissolved in pre- cipitation. they descend as acid solu- tions. In the eastern US.. the acidity of precipitation has achieved a regional pH value below four ( 2 ) . In the Los Angeles Basin, similar pH values exist
due to acid nitrates (3). Emissions rising from stationary
sources are commonly deposited at considerable distances from their sources. The pollutants generated in the Ohio Valley ( 4 ) , for instance. have significantly contributed to the acidity of precipitation in the northeastern US., just as Scandanavian precipita- tion has become contaminated with the emission effluents of Western Europe in the wake of prevailing westerly winds ( 5 ) .
Precipitation in equilibrium with atmospheric COz, the natural cause of acidity, has a pH of 5.65. The weak carbonic acid (H2CO3) that forms by the dissolution of C 0 2 in water has been, until recently, the major cause of marble decay. NO, and SO2 emis- sions, however, have increased the acidity of precipitation. The black crusts and crumbling stone on marble structures in industrialized regions are composed of calcium sulfate, nitrates, and organic particles. Some repre- sentative reactions of these emissions with the marble’s calcite (CaCO3)
380 Environmental Science 8 Technology 0013-936X/81/0915-0386$01.25/0 @ 1981 American Chemical Society
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