Why is marble susceptible to acid rain

When rainwater is too acidic, it can cause problems ranging from killing freshwater fish and damaging crops, to eroding buildings and monuments. Write a balanced chemical equation for the dissociation of nitric acid in water. The gaseous oxides found in the atmosphere, including CO 2 and NO are nonmetal oxides. What would happen to the pH of rainwater if the atmosphere contained metal oxides instead?

Briefly, explain your answer. What causes such a dramatic increase in the acidity of rain relative to pure water? The answer lies within the concentrations of nitric oxide and sulfur dioxide in polluted air. As shown in Table II and Figure 1, the concentrations of these oxides are much higher than in clean air. Humans cause many combustion processes that dramatically increase the concentrations of acid-producing oxides in the atmosphere.

Thus, a large increase in the concentration of NO and SO 2 significantly affects the pH of rainwater, even though both gases are present at much lower concentration than CO 2. About one-fourth of the acidity of rain is accounted for by nitric acid HNO 3.

In addition to the natural processes that form small amounts of nitric acid in rainwater, high-temperature air combustion, such as occurs in car engines and power plants, produces large amounts of NO gas. This gas then forms nitric acid via Equations 4 and 5. Thus, a process that occurs naturally at levels tolerable by the environment can harm the environment when human activity causes the process e.

Most is accounted for by the presence of sulfuric acid H 2 SO 4 in rainwater. Although sulfuric acid may be produced naturally in small quantities from biological decay and volcanic activity Figure 1 , it is produced almost entirely by human activity, especially the combustion of sulfur-containing fossil fuels in power plants.

When these fossil fuels are burned, the sulfur contained in them reacts with oxygen from the air to form sulfur dioxide SO 2. The effects of burning fossil fuels can be dramatic: in contrast to the unpolluted atmospheric SO 2 concentration of 0 to 0.

Sulfur dioxide, like the oxides of carbon and nitrogen, reacts with water to form sulfuric acid Equation 6. At sea level and 25 o C, one mole of air fills a volume of Compute the mole fraction i.

Science Explorer. Multimedia Gallery. Park Passes. Technical Announcements. Employees in the News. Emergency Management. Survey Manual. When sulfurous, sulfuric, and nitric acids in polluted air and rain react with the calcite in marble and limestone, the calcite dissolves. In exposed areas of buildings and statues, we see roughened surfaces, removal of material, and loss of carved details.

Stone surface material may be lost all over or only in spots that are more reactive. You might expect that sheltered areas of stone buildings and monuments would not be affected by acid precipitation. However, sheltered areas on limestone and marble buildings and monuments show blackened crusts that have peeled off in some places, revealing crumbling stone beneath. This black crust is primarily composed of gypsum, a mineral that forms from the reaction between calcite, water, and sulfuric acid.

Gypsum is soluble in water; although it can form anywhere on carbonate stone surfaces that are exposed to sulfur dioxide gas SO2 , it is usually washed away. It remains only on protected surfaces that are not directly washed by the rain. The buildings of our Nation's Capital are constructed with rocks from quarries located throughout the United States and many distant lands.

The earliest Government buildings, however, were constructed with stones from nearby sources because it was too difficult and expensive to move heavy materials such as stone any great distance without the aid Acid deposition, more commonly known as acid rain, occurs when emissions of sulfur dioxide SO2 and nitrogen oxides NOx react in the atmosphere with water, oxygen, and oxidants to form various acidic compounds. Prevailing winds transport the acidic compounds hundreds of miles, often across state and national borders.

These acidic compounds then The U. When scientists learned that acid rain could harm fish, fear of damage to our natural environment from acid rain concerned the American public. They may be found in relatively dry places.

Once established algal growth is able to trap water and establish an environment conducive to the growth of other organisms such as bacteria, lichens, mosses and ferns. Damage to the stone is both chemical and physical. The growth process releases chemicals such as acids and chelating substances which attack the stone.

Penetration of the stone surface by the organism exerts pressure which may lead to fracturing of the stone surface Figure 3. Figure 3: Limestone headstone showing erosion and discolouration from lichen.

Even then factors such as heat, humidity, acidity, salt and dust can continue to cause problems. Heat from spotlights and fireplaces for example, can cause irreversible damage to marble.

The calcite crystals of marble have different directional coefficients of thermal expansion. Acidic vapours can build up in timber showcases or storage areas, especially at high temperatures and relative humidity and damage calcareous stones such as limestone and marble.

Stone analyses are important so that deterioration mechanisms and rates can be determined. Analyses range from the simplest visual inspections and photographic documentation to more high powered techniques like 3-D laser scanning, fluorescence light detection and radar LIDAR , ultrasonic scans, magnetic resonance imaging, thermography and even ground penetrating radar.

While the former techniques to LIDAR are well suited to surface characterisations, the latter techniques are capable of providing information about the interiors of stones.

For many situations however, the outer appearances provide enough information about stone deterioration to guide conservation treatments and the implementation of preventive conservation strategies. The sulfuric acid then further reacts with the limestone in a neutralization reaction. The calcium sulfate is soluble in water and hence the limestone dissolves and crumbles. Effects on Sculptures:. There are many examples in both the U.

Many sculptures have been destroyed, a few have been preserved by bringing them inside.