Acid Rains : An Invisible Threat

Oxides of sulphur and nitrogen are important gaseous pollutants of air. These oxides are produced mainly by combustion of fossil fuels, smelters, power plants, automobile exhaust, domestic fires etc. These oxides are swept up into the atmosphere and can travel a distance of thousands of kilometres. The longer they stay in the atmosphere, the more likely they are to be oxidized into acids. Sulphuric acid and nitric acid are the two main acids, which then dissolve in the water in the atmosphere and fall to the ground as acid rain or may remain in atmosphere in clouds and fogs.
Acidification of environment is man made phenomenon. The acid rain is in fact a Cocktail of sulfuric acid and nitric acid and the ratio of the two may vary depending on the relative quantities of oxides of sulphur and nitrogen emitted. On an average 60 to 70% of the acidity is ascribed to sulfuric acid and 30 to 40% to nitric acid. The acid rain problem has dramatically increased due to industrialisation. Burning of fossil fuels for power generation contributes to almost 60 to 70% of total sulphur dioxide emitted globally. Emission of nitrogen dioxide from anthropogenic sources ranges between 20 to 90 million tonnes annually over the globe. Acid rains have a global ecological problem because oxides travel a long distance and during their journey in atmosphere they may undergo physical and chemical transformations to produce more hazardous products.

Acid rains create complex problems and their impacts are far reaching. They increase soil acidity, thus affecting land flora and fauna;  causes acidification of lakes and streams does affecting aquatic life, affects crop productivity and human health. Besides these they are also corrodes buildings, monuments, statues, bridges, fences, railings etc. British Parliament building also suffered damage due to sulfuric acid rains. Due to acidity, levels of heavy metals like aluminium, manganese, cadmium, lead and copper in water increases beyond the safe limits. Over 10,000 lakes in Sweden have become acidified. Thousands of lakes in USA, Canada, Norway have become unproductive due to acidity. Fish population has decreased tremendously, and there are deaths of Salman trout etc. The fishless areas are now fish graveyards.
Many bacteria and blue green algae are killed due to acidification, the judge disrupting the ecological balance. In West Germany nearly 8% of the forests died and nearly 18 million acres of forest are critically affected by acid rains. Forests in Switzerland, Netherlands and Czechoslovakia have also been damaged by acid rains. Nutrients as calcium, magnesium, potassium have been leached away from the soil by acids.

Acid rains are great threat to  British environment as to  Central Europe and southern Scandinavia. in 1974 acid rains over Scotland were found to be more sour than vinegar.
Acid rains are carried away by 
prevailing winds to elsewhere where precipitation takes place. The oxides may be produced at one place, and these effect elsewhere by turning into acids. The two such victims are Canada and Sweden. Canada gets acid rains from petrochemical units in North America. Heavy winds pickup acid rain from factories in Britain and France to Sweden. Equally grim are the acid rain in Norway, Denmark and West Germany. It is said that 90% of the acid rain of Norway and 75% of Sweden are due to drifted acid rain oxides.

Though acidity of rainwater is yet to be adequately monitored, developing country like ours may soon have to face the acid rain problem. The acid rain is fast spreading to developing world where tropical soils are even more vulnerable than those of Europe. It appears that acid rain problem is on The avil in India. Industrial areas with the pH value of rainwater below or close to the critical value have been recorded in Delhi, Nagpur, Pune, Mumbai and Kolkata. this is due to sulphur dioxide from coal based power plants and petroleum refinery. According to a study made by BARC monitoring section; the average PH value of acid rain in Kolkata is 5.80, Hyderabad 5.73, Chennai 5.85, Delhi 6.21 and Mumbai 4.80. The situation may even worse and in future due to increased installation of thermal power plants by NTPC and consequent increase in coal consumption. According to one estimate total emission of sulphur dioxide in India from fossil fuel burning has increased from 1.38 million tonnes in 1966 to 3.20 million tonnes in 1979, a 21% increase as compared to corresponding increase of only 8.4 % in USA during the same period. There is urgent need for proper regular monitoring to provide timely warnings about acidification of our environment.