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It wreaked havoc in Europe. Now scientists are worried that acid rain may soon acquire grave proportions in India. Acid rainwater may cause irreparable damage to the country's biodiversity, crop yields and the economy. Will we be prepared for it when disaster strikes?
When it rains it burns
Acid rain has already been reported in some parts of India, and the situation is likely to get worse
India faces an increasing threat from acid rain -- earlier believed to be the scourge of the West. The large-scale industrial growth and reliance on the use of coal and crude oil distillates like diesel have led to acidification of the atmosphere.The burning of fossil fuels is mainly responsible for creation of sulphur dioxide ( so 2 ) and oxides of nitrogen ( no x ) which lead to the formation of acid rain. Automobile exhaust fumes are partly to blame, but the worst culprits are coal-burning thermal power plants and the steel industry. Already, a low pH has been observed at Chembur, Maharashtra and Delhi. This is the conclusion of a study conducted by Manju Mohan and Sanjay Kumar of the Centre for Atmospheric Sciences, Indian Institute of Technology ( iit ), New Delhi.
The phenomenon of rain is caused when heat from the Sun's rays on the surface of seas, lakes and rivers induces evaporation. The water vapour formed in the process rises to a height where it condenses into moisture. If ambient conditions prevail it comes down as rain. But in the case of acid rain, water vapour reaches the atmosphere, condenses, and reacts with atmospheric gases like so 2 and no x . When it rains, these atmospheric pollutants are deposited on the soil, vegetation, surface water or reservoirs. The deposition ultimately results in damage because of the acidity of the pollutants (see chart: What goes up must come down ).
The problem is very real in the sub-continent. India enjoys the dubious distinction of releasing the maximum pollutants in the atmosphere after China. Total sulphur emissions are expected to rise from 4,400 kilotonnes (kt) in 1990 to 6,500 kt in 2000, 10,900 kt in 2010 and 18,500 in 2020. It is, therefore, not surprising that low pH levels have been reported from Delhi, Uttar Pradesh, Maharashtra, Madhya Pradesh, Tamil Nadu and even the Andaman Islands. While this will not result in acid rain, the stage has been set for it and if conditions worsen like the setting up of a highly polluting thermal power plant in the vicinity or an industrial estate there may be acid rain. After analysing data from 10 Indian Background Air Pollution Monitoring Stations ( bapmons ), scientists have confirmed that rain in and around these cities is getting increasingly acidic in nature.
The bapmons data collected during 1974-1984 shows that a few areas are already under stress conditions. During two decades, the acidic content of rain in Delhi increased, which means its pH level decreased from 7.0 (1965) to 6.1 (1984), and in nearby Agra from 9.1 (1963) to 6.3 (1984). The data also showed that pH levels in the Andaman Islands fluctuated between 5.6 and 8.9. Acidity and alkalinity are measured on the pH scale from 0 to 14. Normal water is 7 on the scale. Decreasing values on the pH scale denotes increasing acidity and, conversely, higher values show increasing alkalinity. A value below 5.6 denotes acid rain (see graph: Scale of acidity ).
C K Varshney, professor, School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, warns 'Acid rain may cause irreparable damage to the country's biodiversity and even damage the food chain.'
Moreover, the use of diesel is causing a high amount of sulphur and nitrogen emissions in the metros. Indian diesel has a sulphur content of 0.5 per cent by weight. Delhi and Agra are supplied with diesel that has a lower sulphur content. "But even this is far higher than sulphur levels in diesel used in countries like Sweden (0.001 per cent). Swedish diesel is 250 times cleaner. It means that with the rising number of diesel vehicles, the government's objective to bring down sulphur emissions may not be achievable," says H B Mathur, professor emeritus, Delhi College of Engineering. "If the government continues to encourage diesel usage, the prediction made by the iit study may well come true," adds K P Nyati, head (environmental division), Confederation of Indian Industries ( cii ), New Delhi.
The only good news for India is that chances of acid rain occuring are unlikely. This is because tropical climatic conditions and predominantly alkaline-rich soils of the country have a neutralising effect on the pollutants, says R N Gupta, director, Environmental Meteorology Unit, Indian Meteorological Department ( imd). As dust particles in the country are alkaline in nature, acid rain-causing gases such as so 2 and no x get neutralised.
But there is the possibility of the phenomenon occurring in the Northeast and some parts of south India, he says. The imd has, however, not confirmed these findings.