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Each day, thermal power generation, factories and other sources discharge thousands of tones of oxides including sulphur into the atmosphere. Rain is the purest source of water. Acid rain means any precipitation-rain, snow or dew, which is more acidic than normal. Acidity of water is measured on a pH-scale, ranging from 0-14 pH. Neutral solutions and freshly prepared distilled water have a pH of 7.0. Normal rain is slightly acidic (Ph<7) because of the presence of carbon dioxide in the atmosphere. In the absence of pollution the typical pH of rain would be approximately 5.6 (Baukal, 2004). Acid solutions have a pH<7 and alkaline solutions have a pH >7. If pH of rain is less than 5.6, it is termed as acid rain. Now a day, acid rains with pH < 4.5 are common in a lot of developed countries (Bhatia, 2002). Acid rain was initially linked with burning coal in power plants but has since been expanded to include all types of fossil-fuel burning processes, which encompasses all of those considered here.


Sulphur entering the atmosphere are converted to sulphuric and acids, respectively. These acids cause acidic precipitation (acid rain) that is now a major pollution problem in some areas. Headwater streams and high-altitude lakes are especially susceptible to the effects of acid rain and may sustain loss of fish and other aquatic life. Other effects include reductions in forest and crop productivity; leaching of nutrient cations and heavy metals from soils, rocks, and the sediments of lakes and streams; dissolution of metals such as lead and copper from water distribution pipes; corrosion of exposed metal and dissolution of the surfaces of limestone buildings and monuments. As a result of its widespread distribution and effects, acid rain is an air pollutant that may pose a threat to the global atmosphere.

Air pollution has both acute and chronic effects on human health, affecting a number of different systems and organs. Sulfur dioxide primary effect is upon the respiratory tract, producing irritation and increasing airway resistance, mainly to people with respiratory weakness and sensitized asthmatics. Therefore, exposure to the gas may increase the effort required to breathe. Mucus secretion is also stimulated by exposure to air contaminated by sulfur dioxide. Although SO2 causes death in human at 500ppm, it has not been found to harm laboratory animals at 5ppm.