About Acid Rain
The chemical properties of water are uniquely neutral.
A water molecule is made up of three atoms. One oxygen
atom and two hydrogen atoms, which bond together like
magnets. The oxygen bonds with one hydrogen creating
a negative (OH-) and the second hydrogen (H+) provides
the balance of negative and positive charge in water.
In pure water a small number of the H2O molecules split
to form equal numbers of hydrogen (H+) and hydroxide
pH is a scale that is used to measure the concentration
of H+ ions. When the number of H+ and OH- ions in the
water are equal, we say that pH is neutral and assign
it the number 7 on the pH scale. When the concentration
of hydrogen (H+) ions increases, the number on the scale
goes down and we say that something is an acid. When
the concentration of hydrogen (H+) ions decreases, the
pH goes up and we say that something is more basic or
The term or symbol pH is derived from the French words
'pouvoir' meaning power and 'Hydrogéne'. The
measurement numbers on the pH scale range from 1 to
14; the lower the number the harsher the acid; the higher
the number the more basic or alkaline.
Extreme pH levels on both sides of the scale raise concern.
When pH is greater than 9.5 or lower than 4.5 it becomes
unhealthy for organisms that live in the water. young
fish and aquatic insects in early stages of development
are very sensitive to levels below 5 and may die at
the low (highly acidic) levels.
Changes in pH can also affect organisms indirectly.
Low pH levels increase the release of metals from rocks
in a stream or river. These metals can make it more
difficult for the fish to take in water through their
gills which may result in their death.
Pure clean water has a neutral pH of 7, which means
that H+ and OH- are equal. This perfect neutrality is
attainable in a laboratory, but does not exist in nature.
If there was no pollution at all, normal rainwater would
fall slightly on the acidic side of the scale because
it absorbs CO2 as it falls through the air. Pollution
causes the acid level of rain to increase. In some areas
of the world, the rainwater is as acidic as vinegar
or lemon juice.
Where do these acidic gases come from?
* 40% comes from everyday transportation (cars, trucks,
buses, and trains)
* 35% comes from industrial, commercial, and residential
* 25% comes from thermoelectric generating stations
These gases that are floating in the atmosphere dissolve
into the rainwater. When acid rain enters rivers, streams
and lakes it lowers the pH which makes it very difficult
for fish and other forms of life to exist.