Here is a little bit on the history of the acid rain problem. The problem of acid rain probably originated during the 1730's, at the height of the industrial revolution. It was discovered in the 1950's and started being noticed in the 1960's. Since the 1960's, the problem has gotten worse in rural areas because the tall chimneys on factories allow the wind to transport pollutants far away from their sources. In 1984 it was reported that almost half of the trees in the famous black forest in Germany had been damaged by acid rain. In 1988, as part of the United Nations-sponsored Long Range Transboundary Air Pollution Agreement, the U.S.A. and 24 other nations agreed to some rules limiting nitrogen oxide emissions to 1987 levels.1990 changes to the Clean Air Act set rules to cut down the release of sulfur dioxide from power plants down to 10 million tonnes by January 1, 2000.