Acid Precipitation – An International Environmental Problem

Abstract

The acidification is no longer confined to Scandinavia, it is a trans-World problem. The concept of acidification is bound up with the discharge into the atmosphere of sulphur dioxide, nitrogen oxides, and metals and other micro-pollutants - and the subsequent effects of these substances on the environment. The bulk of man-made emissions occurs over industrialized regions covering less than 5% of the earth's surface. In these regions, man-made emissions exceed the natural emissions by a factor of five to twenty. In the 1950's a sharp rise in oil combustion increased the SO2 emissions in Europe to about 25 million tonnes of sulphur per year by 1970. European emissions of NO have increased from low values 100 years ago to the present value of about 6 million tonnes of nitrogen per year. Similar emission trends of SO2 and NOx have taken place in North America. Sulphur dioxide emissions in Europeare predicted to remain about the same as present-day emission through 1990. Further trends in emission will depend critically on the energy policies of each country and the entire region. Strong acids have decreased the mean annual pH of precipitation in much of Northwestern Europe and large areas of North America to between 4 and 4.5. The sources and environmental consequences of acid deposition are often separated by hundreds, even thousands, of kilometres. Its impacts on aquatic systems in more susceptible areas of Europe and North America are clearly documented today. Tomorrow, the emission source areas exposed to the heaviest depositions will be facing serious direct and indirect effects on natural ecosystems, materials and possibly even human health. Further, metal toxicity in soils, surface waters and groundwaters with consequences for terrestrial and aquatic life will most likely develop in both heavily polluted and sensitive areas.