How is acid rain made

Exhausts from cars cause the formation of nitrogen oxides in the air. From these gases, airborne sulfuric acid H 2 SO 4 and nitric acid HNO 3 can be formed and be dissolved in the water vapor in the air.

Although acid-rain gases may originate in urban areas, they are often carried for hundreds of miles in the atmosphere by winds into rural areas. That is why forests and lakes in the countryside can be harmed by acid rain that originates in cities.

The environment can generally adapt to a certain amount of acid rain. Often soil is slightly basic due to naturally occurring limestone, which has a pH of greater than 7. Because bases counteract acids, these soils tend to balance out some of the acid rain's acidity. But in areas, such as some of the Rocky Mountains and parts of the northwestern and southeastern United States, where limestone does not naturally occur in the soil, acid rain can harm the environment.

Some fish and animals, such as frogs, have a hard time adapting to and reproducing in an acidic environment. Many plants, such as evergreen trees, are damaged by acid rain and acid fog.

I've seen some of the acid-rain damage to the evergreen forests in the Black Forest of Germany. Much of the Black Forest was indeed black because so much of the green pine needles had been destroyed, leaving only the black trunks and limbs!

You also might notice how acid rain has eaten away the stone in some cities' buildings and stone artwork. Acidity in rain is measured by collecting samples of rain and measuring its pH.

To find the distribution of rain acidity, weather conditions are monitored and rain samples are collected at sites all over the country. The areas of greatest acidity lowest pH values are located in the Northeastern United States.

This pattern of high acidity is caused by the large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast.

In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain. When you hear or read in the media about the effects of acid rain, you are usually told about the lakes, fish, and trees in New England and Canada. However, we are becoming aware of an additional concern: many of our historic buildings and monuments are located in the areas of highest acidity.

In Europe, where buildings are much older and pollution levels have been ten times greater than in the United States, there is a growing awareness that pollution and acid rain are accelerating the deterioration of buildings and monuments. Stone weathers deteriorates as part of the normal geologic cycle through natural chemical, physical, and biological processes when it is exposed to the environment. This weathering process, over hundreds of millions of years, turned the Appalachian Mountains from towering peaks as high as the Rockies to the rounded knobs we see today.

Our concern is that air pollution, particularly in urban areas, may be accelerating the normal, natural rate of stone deterioration, so that we may prematurely lose buildings and sculptures of historic or cultural value. This religious medieval sculpture, made of sandstone, has been degraded by the acidification of air and rains. Many buildings and monuments are made of stone, and many buildings use stone for decorative trim.

Granite is now the most widely used stone for buildings, monuments, and bridges. Limestone is the second most used building stone. It was widely used before Portland cement became available in the early 19th century because of its uniform color and texture and because it could be easily carved. Sandstone from local sources was commonly used in the Northeastern United States, especially before Nationwide, marble is used much less often than the other stone types, but it has been used for many buildings and monuments of historical significance.

Because of their composition, some stones are more likely to be damaged by acidic deposition than others. Granite is primarily composed of silicate minerals, like feldspar and quartz, which are resistant to acid attack. Sandstone is also primarily composed of silica and is thus resistant. A few sandstones are less resistant because they contain a carbonate cement that dissolves readily in weak acid. Limestone and marble are primarily composed of the mineral calcite calcium carbonate , which dissolves readily in weak acid; in fact, this characteristic is often used to identify the mineral calcite.

Acid precipitation affects stone primarily in two ways: dissolution and alteration. The sulfuric and nitric acids formed in the atmosphere fall to the ground mixed with rain, snow, fog, or hail. Acidic particles and gases can also deposit from the atmosphere in the absence of moisture as dry deposition. The acidic particles and gases may deposit to surfaces water bodies, vegetation, buildings quickly or may react during atmospheric transport to form larger particles that can be harmful to human health.

When the accumulated acids are washed off a surface by the next rain, this acidic water flows over and through the ground, and can harm plants and wildlife, such as insects and fish. The amount of acidity in the atmosphere that deposits to earth through dry deposition depends on the amount of rainfall an area receives. For example, in desert areas the ratio of dry to wet deposition is higher than an area that receives several inches of rain each year.

Unlike wet deposition, dry deposition is difficult and expensive to measure. When acid deposition is washed into lakes and streams, it can cause some to turn acidic. The Long-Term Monitoring LTM Network measures and monitors surface water chemistry at over sites to provide valuable information on aquatic ecosystem health and how water bodies respond to changes in acid-causing emissions and acid deposition.

Air-quality standards have also driven U. These trends have helped red spruce forests in New England and some fish populations , for example, recover from acid rain damage. But recovery takes time, and soils in the northeastern U. Acid rain problems will persist as long as fossil fuel use does, and countries such as China that have relied heavily on coal for electricity and steel production are grappling with those effects.

One study found that acid rain in China may have even contributed to a deadly landslide. China is implementing controls for sulfur dioxide emissions, which have fallen 75 percent since —but India's have increased by half.

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