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 (OH-) ions.

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 alkaline.


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 combustion processes
* 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.