Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 34

Acid rain is formed when sulfur dioxide (SO₂) and the nitrogen oxides (NO_x) react with water vapor and oxidants in the presence of sunlight to produce various acidic compounds, such as sulfuric acid and nitric acid.

Acid rain has a pH less than 5.0 and predominantly consists of sulfuric acid (H₂SO₄) and nitric acid (HNO₃). As a point of reference, in the absence of anthropogenic pollution sources the average pH of rain is approximately 6.0 (slightly acidic; neutral pH = 7.0). In summary, the sulfur dioxide that is produced during a variety of processes will react with oxygen and water in the atmosphere to yield environmentally detrimental sulfuric acid. Similarly, nitrogen oxides will also react to produce nitric acid.

Precipitation in the form of rain, snow, ice, and fog causes approximately 50% of these atmospheric acids to fall to the ground as acid rain, while approximately 50% fall as dry particles (particulate matter, such as soot or aerosol particles) and gases. Winds can blow the particles and compounds hundreds of miles from their source before they are deposited, and they and their sulfate and nitrate derivatives contribute to atmospheric haze prior to eventual deposition as acid rain. The dry particles that land on surfaces are also washed off by rain, increasing the acidity of runoff.

The principle source of acid rain causing pollutants, sulfur dioxide and nitrogen oxides, are coal-fired power plants. Since natural gas emits virtually no sulfur dioxide, and up to 80% less nitrogen oxides than the combustion of coal, increased use of natural gas could provide for fewer acid rain–causing emissions.