Acid Rain and Gray Snow 
In many parts of the world, rain is no 
longer gentle and snow no longer white 
by George R. Hendrey 
Mountain lakes and streams, long 
regarded as symbols of purity, are be- 
coming increasingly contaminated by 
atmospheric pollution. Rain and snow 
that have become loaded with toxic 
chemicals, mainly acids, have been 
falling over nearly all of the eastern 
United States, southeastern Canada, 
northern Europe, and southern Scan- 
dinavia. More recently, California, 
Colorado, and Washington State have 
been added to the list of regions known 
to be receiving acidic precipitation. 
In many places, the rain is so polluted 
that numerous species of freshwater 
animals would be killed if they were 
exposed directly to water having its 
average chemistry. 
The pollution is caused primarily 
by the combustion of large amounts 
of fossil fuels — coal, oil, and gas. Ox- 
ides of sulfur and nitrogen created 
in the combustion process are released 
into the atmosphere, where they react 
with oxygen, water, and other sub- 
stances in the air to form sulfuric acid 
and nitric acid. These two pollutants 
are what cause the rain to be so acidic. 
In 1940, about 22 million tons of 
sulfur oxides and about 6.7 million 
tons of nitrogen oxides were spewed 
into the atmosphere from American 
homes, factories, and power plants. 
By 1976 these emissions had risen to 
32 million tons of sulfur oxides, a 45 
percent increase, and 25 million tons 
of nitrogen oxides, a 273 percent in- 
crease. Large increases in power plant 
emissions of sulfur oxides during this 
period were partly offset by decreased 
Streams in certain mountainous 
areas, including the Adirondacks, 
are particularly sensitive to 
acidification. The drainage 
basins of such streams typically 
have relatively little soil cover 
and a minimum of minerals 
capable of neutralizing 
the acidity of precipitation. 
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