Acid Rain

Fossil fuels are mixtures of various chemicals, including small amounts of

sulfur. The sulfur in the fuel reacts with oxygen to form sulfur dioxide

(SO

power plants that burn high-sulfur coal. The Clean Air Act of 1970 has limited

the SO

2), which is an air pollutant. The main source of SO2 is the electric2 emissions severely, which forced the plants to install SO2

scrubbers, to switch to low-sulfur coal, or to gasify the coal and recover the

sulfur. Motor vehicles also contribute to SO

diesel fuel also contain small amounts of sulfur. Volcanic eruptions and hot

springs also release sulfur oxides (the cause of the rotten egg smell).

The sulfur oxides and nitric oxides react with water vapor and other

chemicals high in the atmosphere in the presence of sunlight to form sulfuric

and nitric acids (Fig. 2–65). The acids formed usually dissolve in the

suspended water droplets in clouds or fog. These acid-laden droplets, which

can be as acidic as lemon juice, are washed from the air on to the soil by

rain or snow. This is known as

a certain amount of acid, but the amounts produced by the power plants

using inexpensive high-sulfur coal has exceeded this capability, and as a

result many lakes and rivers in industrial areas such as New York, Pennsylvania,

and Michigan have become too acidic for fish to grow. Forests in

those areas also experience a slow death due to absorbing the acids through

their leaves, needles, and roots. Even marble structures deteriorate due to

acid rain. The magnitude of the problem was not recognized until the early

1970s, and serious measures have been taken since then to reduce the sulfur

dioxide emissions drastically by installing scrubbers in plants and by desulfurizing

coal before combustion.

2 emissions since gasoline andacid rain. The soil is capable of neutralizing