The problem of acid rain that severely encountered the industrial countries of the West during 1960s, 1970s and 1980s has become a major cause of concern in the countries of Asia and Pacific region which are currently going through the process of rapid industrial development. On the other hand, in the developed countries, where it seems to be controlled, the actual story is something different.
The Problem
Acid rain, though by name, is one kind of wet deposition of some acids; it may well take the form of dry deposition also. Examples of dry deposition are soot and ash, sleet, hail, snow, smog, and low level ozone etc. However, generally by acid rain we simply mean the precipitation of acid in the form of rain. The question then naturally arises why does such precipitation take place? The second question is how could one measure the acidity level of rain water?
Acid rain is primarily the outcome of emission of various gaseous oxides in the atmosphere. The list mainly includes sulfur dioxide (SO2) and different oxides of nitrogen (NOx).Moreover, some volatile organic compounds (VOC) like vapours from gasoline, industrial chemicals such as benzene, tetrachloroethelene etc. are also responsible for acid rain.
Sources of acid rain
Major sources of the pollutants responsible for acid rain are power stations and industries that burn fossil fuels such as coal oil and natural gas. Another major source is vehicles that use gasoline and diesel. In addition to these major sources, two other minor sources can be mentioned. One is household source, another is natural source. Household source mainly includes home fires which emit smoke full of sulfur dioxide. Natural sources are, however, many in number. Volcanoes, forest fires, swamp gases release sulfur dioxide in the atmosphere; whereas microorganisms in soils, lighting during thunderstorms release oxides of nitrogen. The contribution of various sources, however, differs from country to country. For example, in USA and Europe the main source is power stations, whereas in Canada it is the metal smelting industries which are the main culprits.
Oxides of sulfur and nitrogen, after being released into the atmosphere by different sources come in contact with moisture of air and of cloud. In reaction with this air moisture and oxygen these oxides transform themselves into acids like sulfuric and nitric acids. Then these acids precipitate on the earth surface along with rain.
Likely Consequences of Acid Rain
A raindrop is said to be acidic when its pH level falls below 5.7. Acid rain makes soil and water bodies acidic which, in turn, has damaging effect on plants and animals’ health. In fact, awareness regarding acid rain in European countries began to rise after the incident of Waldsterben (forest death) that began to start from the end of the 1970s in West Germany. Similar kind of forest death was, however, experienced by the Central Europe in the early 1930s. Acid rain primarily pollutes soil and water. Pollution of water bodies from acid rain comes as a threat to aquatic life. Today a large number of lakes in Sweden are completely out of fish after their water become acidic. Acid rain, on the other hand, leaches valuable minerals like calcium, magnesium, potassium out from soil and, by this process, soil looses its fertility. A study reveals that in some agricultural fields of India where SO2 deposition is five times greater than the critical level due to their proximity to a power plant had lost their fertility by almost half. Wheat production in that area is observed to be 49 percent less in comparison to an area just 22 km away. Plants and trees that came in direct contact with acid rain are seen to be less effective at photosynthesis.
Combating acid rain: International initiatives
It was in the year 1852 when the event of acid rain was first seen in Manchester, England. Robert Angus Smith, a British scientist, discovered it and explained its relationship with atmospheric pollution. However, serious research and investigation on this event started only after a century, during 1960s. In 1962, S.Oden, a Swedish scientist, found, on the basis of data compiled during the decade of 1950 that in Scandinavia acid rain had been taking place from the air masses that came out of Central and Western Europe. By this time Harold Harvey of Canada started his research on dead lakes. In fact, until the twentieth century, acid rain was a local phenomenon. Emission of smoke from factories concentrated in the lower atmosphere, close to the earth surface. As a result only nearby areas were getting polluted. In order to get rid of this pollution problem several countries, like the USA, the UK resorted to tall chimney policy. The argument behind this policy was that taller smokestacks would disperse gaseous so widely that they got diluted and did no further harm. But in practice this thought was ultimately proved to be wrong. By the 1960s it was discovered that pollutants thrown over by taller smokestacks were, in fact, crossing national boundaries and were posing serious threat to the environment of neighboring countries. Pollutants of the UK and mainland Europe were polluting Sweden and Norway and that of the USA were causing acidification in Canada.
Internationalization of the problem in this way soon drew the attention of international community. The issue was raised by Sweden and Norway, two worst victims of acid rain, in the Rio conference in 1972 in order to frame some international rules in this regard. In support with this demand a meeting was by Economic Commission for Europe, an UN body, at Geneva in 1979. An agreement, Convention on Long-Range Transboundary Air Pollution (LRTAP) was signed accordingly. However, it was only a framework convention. A framework convention is one which only acknowledges the emergence of a problem and encourages the signatories to take voluntary steps to control the potential problem.
The LRTAP convention was signed in 1980, but almost nobody was there to follow the convention. However, damages from acid rain were increasing day by day. Many countries that were not ready to control their emission level initially are now gradually realising the importance of emission-reduction programme and also of international co-operation in this regard. In 1983 Norway proposed a 30 percent reduction of SO2 by 1993 compared to the 1980 level. The proposal, though sternly opposed by some other countries like the UK, the USA was finally accepted by the LRTAP convention. The convention adopted a protocol called Sulphur Protocol, in this regard in 1985 and asked its signatories of the 1980 convention to ratify this in their own countries. Similar kind of protocols on NOx and VOC emissions were also signed respectively in 1988 and1991. In 1990 the USA amended her Clean Air Act of 1970. The objective was to reduce SO2 emission.
However, all these efforts were not international in true sense, because in all the cases only a few countries united together and signed a protocol. But solution to this problem can not be reached by such isolated efforts.
The Future
Incidents of acid rain in developed countries have started declining in number. In fact SO2 emission in these countries can be checked by taking several remedial mesures, but NOxemission cannot be. Moreover, damages that have already been caused by acid rain are yet to be recovered.
However, the situation is particularly alarming in developing countries, particularly of Asia and Pacific region. The consequences of such heavy deposition are not difficult to understand. Asia is now considered to be the global hotspot of S and N deposition. The deposition of of both S and N is found to be globally maximum in East Asia since the early 2000s. Trends of SO2 and NOx emissions, however, varied significantly among countries in Asian region. In 2005, for example, more than 35 percent of the global emissions were contributed mainly by two Asian giants, namely China and India. SO2 emissions of China, Japan and South Korea however, started declining thereafter due to wide application of flue-gas desulfurization in power plant units. Recently NOx emissions in these three countries were also observed declining due to applications of selective catalytic reduction in coal-fired power plants and stringent emission standards implemented for vehicles.
No doubt, these progresses are worthmentioning. But this, by no means, indicates a pepetual solution to the problem. Problem of acid rain is the outcome of air pollution and hence transboundary in nature. Therefore, only a harmonizing effort by the countries over the world can bring an end to this road.
Anindya Bhukta