ABATEMENT AND TRENDS IN EMISSION
Figure 5 shows the change in global emissions of SO2, NOx, and NH3 for the different source categories. The figure shows that there is a steady increase in emissions for the three gases between 1890 and 1995. The contribution of energy emissions is highest during the whole time period for SO2 and NOx; for NH3, energy constitutes only a minor contribution. After World War II, the increase in emission is higher.
After 1990, there seems to be a smaller increase in global emissions. This is mainly due to the decrease
3% 3% 6%0%5%0%
of emissions of SO2 and, to a lesser extent, NOx in the United States and Europe. This leveling is a net effect of decreased emissions in the industrialized areas of Europe and the United States and increased emissions in developing countries, especially Asia. Table I shows the estimated changes in emissions between 1990 and 1998 in Europe, the United States, and Asia. Europe shows the most positive trends in the world. Emission trends in the United States between 1990 and 1998 are somewhat upward for the nitrogen components, whereas SO2 and volatile organic compounds (VOCs) show a downward trend of 18 and 14%, respectively. Emissions of SO2, NOx, NH3, and VOCs show a downward trend of 41, 21, 14, and 24%, respectively. Clearly, policy has been much more successful in Europe than in the United States.
Table I shows that emissions of SO2 and VOCs in the United States and Europe have decreased, whereas in Asia they have increased. The nitrogen components decreased only in Europe, whereas in the United States they remained about the same. In Asia, NOx emissions more than doubled, whereas for NH3 no data are available. There is a distinct difference between the policies in the United States and those in Europe to combat acidification. In the United States, the Clean Air Act is the driving force to reduce emissions, and in Europe the reductions are
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achieved through protocols under the Convention of Long-Range Transboundary Air Pollution, with the multipollutant-multieffect protocol signed in 1999 in Gothenburg being the most recent.