Sulfur Emissions

Sulfur emissions to the atmosphere in the US due to anthropogenic sources have also increased, as was shown in Figure 8. Emissions of sulfur per year from 1860 to 1980 in the US have risen from about 10 Tg to a peak of about 32 Tg in 1970. Environmental regulations have reduced these emissions substantially in recent years in the US and many developed countries that can afford to install sulfur emissions abatement equipment. Developing countries experiencing rapid growth or that use high-sulfur coal and low-technology combustion equipment are contributing to growing emissions.

The main global source of anthropogenic sulfur is burning of high-sulfur coal, which contributes 70-80 Tg of sulfur per year, mostly in the form of sulfur dioxide ($SO$₂). Biomass burning contributes 0 .8 to 2.5 Tg to the global total. Natural sources include ocean production of dimethyl sulfide (DMS), soil and plant production of DMS and hydrogen sulfide ($H$₂S). Volcanoes, which of course are episodic sources, may contribute 7 to 10 Tg annually. Figure 9 clearly shows that anthropogenic emissions now dominate natural sources of sulfur in the atmosphere.

Sulfur compounds, like $SO$₂ , are short-lived species in the atmosphere that are subject to chemical transformation, washout, and dry deposition and lead to acid precipitation problems. SO₂ is a gas that condences to particulate SO₄ within a few hours after being emitted into the atmoshpere. We know of sulfur dioxide as a pollutant because it reacts with water ($H$₂O) to form sulfuric acid ($H$₂SO₄). If we were able to switch off all the power plants and other anthropogenic as well as natural sources of sulfur, we could eliminate most of the sulfur from the atmosphere in a couple of weeks.

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