EMISSIONS FROM ENERGY USE
van Ardenne et al. provide a compilation of global sulfur emissions, mainly based on work by different authors. According to their estimates, anthropogenic contributions are on the order of 75% of the total sulfur emissions, 82% of which is related to energy production and use (Fig. 3). Anthropogenic emissions exceeded natural emissions as early as 1950. Important natural sources are volcanoes and DMS emissions from the oceans. Fossil fuel use in industry, fuel production in refineries, and electricity generation are the main activities responsible for anthropogenic emissions. According to EMEP (Cooperative Program for Monitoring and Evaluation of Air Pollutants in Europe) studies, the maximum sulfur emissions in western Europe occurred from 1975 to 1980, at a level of 40 million tons of SO2. The emissions have decreased since then and are
currently at a level of approximately 30 million tons of SO2.
On a global scale, NOx emissions are estimated to be equally divided between anthropogenic and biogenic sources. However, anthropogenic contributions are already much higher than the natural emissions in the Northern Hemisphere. Most natural emissions, through biomass burning, occur in agricultural areas of South America and Africa. In western Europe and the United States, traffic is the main source for NOx, contributing 50% or more of the total NOx emissions.
Globally, in 1995 the emissions from fossil fuels contributed 82, 59, and 0.1% to the total emissions of SO2, NOx, and NH3, respectively. The contributions of fuel and other anthropogenic sources to the emissions of the three gases are shown in Fig. 4.