Acid Rain

Acid rain is any form of precipitation- rain, snow, sleet, fog – which contains high levels of acid. Precisely, it is precipitation with dilute solutions of two strong acids- sulphuric acid and nitric. Of these acids, 70 per cent derive from oxidation and hydrolysis of sulphur dioxide and hydrogen sulphide, 30 per cent from various nitric oxide and other compounds. Both sulphur and nitrogen emissions are attributed to the burning of fossil fuels particularly high sulphur coal and oil and the latter is tied directly to the industrial development. There has been a rise in the carbon dioxide and sulphur and nitrogen oxides in the last 150 years during which fossil fuel consumption has been increased. Ammonia from livestock sources and agricultural fields, hydrogen from sea spray, volatile organic compounds( alkanes, polychlorinated alkanes, esters and hydrocarbons) also add up to the “acid rain cocktail”. In acid rain, which contain sulphuric acid, the fist ingredient is the sulphur dioxide gas emitted by power stations, cars and lorries.

When it meets highly reactive chemical agents called OH radicals in the atmosphere it is oxidised to from sulphur trioxide, which is also a gas. This then combines with rain to form sulphuric acid. It is estimated that raindrops containing even 12 molecules of water, in this situation can bring about sulphuric acid almost effectively as in large droplets containing nearly 200 molecules. This water cluster appears to have a double role. The fist two molecules are catalytic and the extra ten molecule cluster round the reactant acting like a solvent. When two water molecules and the single molecule of sulphur tri oxide combine a short lived ring compound is formed which breaks up to leave the sulphuric acid and water molecule. This reaction is faster in large droplets of rain water which results in the formation of acid rain. If the rain water is very pure its PH value should be 7, but theoretically it is slightly lower than 7 i.e. it is mildly acidic. In industrially advanced cities like Toronto and Los Angeles of the USA sometimes average pH of the rain water becomes 3.5 and 2.2 respectively.
The most acidic rain fall occurred in US. to date in 1.4 in West Virginia which is not much above the acidity of the battery which has a pH value of 1. In India the lowest natural rain of pH 3.5 was recorded in Chembur in Mumbai and Indraprasth in Delhi. Acid rain will cause direct damages architectural structures by corroding famous monuments. Most fish species die when the pH is less than 5. The aerosol of acid rain can cause respiratory disorders in man. Taj Mahal has been polluted. its colour has lost.

If drinking water is drawn from ponds and lakes, then the aluminium leaching is likely to pose dangers. Aluminium toxicity is linked to kidney failure and bone softening. Copper leached from water pipes containing acid rain water can cause diarrhoea in children.

Clean dry air is composed of nitrogen, oxygen, argon, carbon monoxide and traces of other elements in various per cent ages. The five most important air pollutants are carbon monoxide (CO2), sulphur oxides, hydrocarbons, nitrogen oxides and particles, both liquid and solid of industrial dusts, ash and spray. The major sources from which these are derived are automobile industry, electrical power plants, space heating and refuse. Complex reaction occur between these contaminants and water vapour that leads to the formation of carbonic acid (H2CO3), sulphuric acid ( H2SO4), nitric acid etc. These factors are the primary factors in acid rain which is now recognised as one of our most serious environmental factors. Acid rain creates complex problems and their impacts are far reaching.