From information gathered in the
1930's and 1950's, it appears that the acidity of
rainfall in the eastern United States has increased
significantly (in Great Smoky Mountains National Park:
1956 - 5.6; 1980 - 4.27). Some scientists dispute
this theory, however.
The gases sulfur dioxide (SO2) and
various nitrogen oxides (NOx) are mainly responsible
for the increase in acidity.
These gases are primarily created
by industrial factories, coal-fired power plants,
and car emissions.
It has been estimated that approximately
26 million tons of SO2 and 22 million tons of NOx
were put into the atmosphere in the United States
in 1980. (If 1 ton = 20 students each weighing 100
lbs., how many students = 48 million tons of polluntants?
Answer: 960 million or approximately 1 billion students).
Some scientists believe that natural
sources of SO2 and NOx (forest fires, lightning, volcanoes,
etc.) have an equally important effect on acid rain
(pH levels) as manmade sources.
Areas where the soil has been disturbed
(mines, forest fires, landslides, construction sites)
may be making water in streams and lakes more acidic.
Many soils are already acidic or contain minerals
which react with rainwater, snowmelt, etc., to form
acids. These acidic waters are carried into stream
The gases SO2 and NOx are thought
to be carried long distances by air currents. Storm
systems also move long distances, carrying with them
any pollutants they may pick up. The interaction of
airborne pollutants and clouds is not well understood.
Understanding the movement of prevailing
air currents and storm systems can greatly aid scientists
in discovering where acid rain is coming from and,
just as importantly, where the rain is returning to
Scientists hope to learn more about
the movements of acid rain by studying storm events,
high and low pressure movements (high pressure usually
is an indication of good, clear weather, whereas low
pressure fronts are associated with storms), and occluded
fronts. Occluded fronts normally precede storm events,
thus making them a good indicator for tracking storm
Researchers are attempting to track
where the pollution (gases, fly-ash, soot, and dust particles)
goes when it leaves the heavy industrial and populated
areas by making projections of storm event and air