Acid Rain

11 Pages 2864 Words

omes from power plants, especially those that burn coal. In Canada, industrial activities, including oil refining and metal smelting, account for 61 percent of sulfur dioxide pollution. Nitrogen oxides enter the atmosphere from many sources, with motor vehicles emitting the largest share?43 percent in the United States and 60 percent in Canada.

Once in the atmosphere, sulfur dioxide and nitrogen oxides undergo complex reactions with water vapor and other chemicals to yield sulfuric acid, nitric acid, and other pollutants called nitrates and sulfates. The acid compounds are carried by air currents and the wind, sometimes over long distances. When clouds or fog form in acid-laden air, they too are acidic, and so is the rain or snow that falls from them.

Acid pollutions also occur as dry particles and as gases, which may reach the ground without the help of water. When these dry acids are washed from ground surfaces by rain, they add to the acids in the rain itself to produce a still more corrosive solution. The combination of acid rain and dry acids is known as acid deposition.

The acids in acid rain react chemically with any object they contact. Acids are corrosive chemicals that react with other chemicals by giving up hydrogen atoms. The acidity of a substance comes from the abundance of free hydrogen atoms when the substance is dissolved in water. Acidity is measured using a pH scale with units from 0 to 14. Acidic substances have pH numbers from 1 to 6 the lower the pH number, the stronger, or more corrosive, the substance. Some non-acidic substances, called bases or alkalis, are like acids in reverse - they readily accept the hydrogen atoms that the acids offer. Bases have pH numbers from 8 to 14, with the higher values indicating increased alkalinity. Pure water has a neutral pH of 7?it is not acidic or basic. Rain, snow, or fog with a pH below 5.6 is considered acid rain.

When bases react with acids, the bases less...