Volcanic sulfur emissions, source

Graf H.-F., Feichter J., and Langmann B. (1997) Volcanic sulfur emissions estimates of source strength and its contribution to the global sulfate distribution. J. Geophys. Res. 102, 10727-10738. 

According to different estimates, the river runoff to the ocean changes from 0.104 X10 tons S/yr. (Ivanov, 1983) up to 0.162 x 10 tons S/yr. (Dobrovolsky, 1994). A significant amount of various sulfur compounds are input through hydrothermal sources, up to 130 x 10 tons/yr. The volcanic sulfur emission to the continental atmosphere is estimated as 0.001 x 10 tons annually and a similar number applied to for oceanic atmosphere (Fried, 1973). 

Natural emissions of sulfur compounds to the atmosphere occur from a variety of sources, including volcanic eruptions, sea spray, and a host of biogenic processes (e.g., Aneja, 1990). Most of the volcanic sulfur is emitted as S02, with smaller and highly variable amounts of hydrogen sulfide and dimethyl sulfide (CH3SCH3). Sea spray contains sulfate, some of which is carried over land masses. 

Sulfur species are found in ambient air in most parts of North America and in most industrial countries. Their sources include natural emissions (biogenic and volcanic), smelting of ores and other industrial refining processes, and combustion of sulfurbearing fuels. This paper will focus on the combustion sources in the United States and some of the effects of their sulfur emissions. The environmental effects of sulfur in the environment have been of interest for many years and much of the information presented here has been drawn from the various conference proceedings and assessment documents that have been published in recent years (1-11). When specific references are not listed in the text, the information represents a consensus from these various sources. 

Acid rain is caused primarily by sulfur dioxide emissions from burning fossil fuels such as coal, oil, and natural gas. Sulfur is an impurity in these fuels for example, coal typically contains 2-3% by weight sulfur. Other sources of sulfur include the industrial smelting of metal sulfide ores to produce the elemental metal and, in some parts of the world, volcanic eruptions. When fossils fuels are burned, sulfur is oxidized to sulfur dioxide (SO2) and trace amounts of sulfur trioxide (S03)J21 The release of sulfur dioxide and sulfur trioxide emissions to the atmosphere is the major source of acid rain. These gases combine with oxygen and water vapor to form a fine mist of sulfuric acid that settles on land, on vegetation, and in the ocean. 

Despite being recognized as far back as the 1870s, the environmental problems associated with acid rain came to the fore in the 1960s with the decline of fish stocks in European and North American lakes. Two of the major contributors towards acid rain are SO2 and NO . (In Section 25.8, we discuss the use of catalytic converters to combat pollution due to nitrogen oxides, NOj .) Although SO2 emissions arise from natural sources such as volcanic eruptions, artificial sources contribute 90% of the sulfur in the atmosphere. Fossil fuels such as coal contain 2-3% sulfur and combustion produces SO2. This is being countered by the recovery of sulfur from petroleum (Fig. 16.2). Sulfur dioxide is released when metal sulfide ores are roasted in the production of metals such as Co, Ni, Cu and Zn, for example ... 

Sulfur dioxide Is formed primarily from the Industrial and domestic combustion of fossil fuels. On a global scale, man-made emissions of SOj are currently estimated to be 160-180 million tons per year. These emissions slightly exceed natural emissions, largely from volcanic sources. The northern hemisphere accounts for approximately 90% of the man-made emissions (13-14). Over the past few decades global SOj emissions have risen by approximately 4%/year corresponding to the Increase In world energy consumption. 

Acid rain is actually a catchall phrase for any kind of acidic precipitation, including snow, sleet, mist, and fog. Acid rain begins when water comes into contact with sulfur and nitrogen oxides in the atmosphere. These oxides can come from natural sources such as volcanic emissions or decaying plants. But there are man-made sources as well, such as power plant and automobile emissions. In the United States, two-thirds of all the sulfur dioxide and one-fourth of the nitrogen oxides in the atmosphere are produced by coal-burning power plants. 

Sulfur dioxide is produced by both natural and anthropogenic sources. The most important of the natural sources are volcanic eruptions, which account for about 40 percent of all natural emissions of the gas. Since volcanic eruptions are episodic events, the amount of sulfur dioxide attributable to this source in any one year varies widely. Other natural sources of the gas are forest fires and other natural burns, biological decay, and certain metabolic processes carried out by living organisms, especially marine plankton and bacteria. Natural sources release about 27.5 million short tons (25 million metric tons) of sulfur dioxide per year. 

Carbonyl sulfide is also the most abundant reduced sulfur gas in Earth s troposphere, but for completely different reasons. Volcanic sources of OCS are negligible by comparison with biogenic emissions, which are important sources of several reduced sulfur gases (e.g., OCS, H2S, (CH3)2S, (CH3)2S2, and CH3SH) in the terrestrial troposphere. Many of these gases are ultimately converted into sulfate aerosols in the troposphere, but OCS is mainly lost by transport into the stratosphere, where it is photochemically oxidized to SO2 and then to sulfuric acid aerosols, which form the Junge layer at —20 km in Earth s stratosphere. 

During the thermally driven differentiation of the Earth into core-mantle-crust, numerous reactions would have produced oxidized forms of iron, sulfur and carbon. These would have contributed to the redox chemistry in the early planet development. Volcanic and hydrothermal emission of sulfur dioxide, SO2, delivered oxidants to the oceans and atmosphere. Photodissociation of water vapor in the atmosphere have undoubtedly provided a small but significant source of molecular oxygen. Furthermore, UV-driven ferrous iron oxidation could have been coupled to the reduction of a variety of reactants, for instance, CO2 (Figure 16). 

CH3)2S by marine organisms, together with volcanic emissions (mostly S02). These natural sources are now exceeded by the emission of S02 from burning sulfur-containing fossil fuels. Most... 

Table 10-17 includes a global atmospheric sulfur budget based on the emission estimates discussed in this chapter and the flux diagrams shown in Figs. 10-8 and 10-9. The marine budget of 36 Tg S/yr supplied by the biosphere must be augmented by about 6.8 Tg S/yr from anthropogenic sources. In addition, about one-half of the sulfur from volcanic emissions... 

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