Sulfur Dioxide (2)

What produces sulfur dioxide?

The two natural sources of SO₂ are volcanic eruptions and sulfur containing geothermal sources like geysers and hot springs. Emission rates of sulfur dioxide from an active volcano range from 20 tonnes per day to 10 million tonnes per day according to the style of volcanic activity and type and volume of magma involved.

For example, the large explosive eruption of Mount Pinatubo on 15 June 1991 expelled 3-5 km3 of dacite magma and injected about 20 million metric tons of sulfur dioxide into the stratosphere. Together with the increased stratospheric chlorine levels from human-made chlorofluorocarbon (CFC) pollution, the sulfate aerosols dispersed from the volcanic eruption destroyed ozone and led to some of the lowest ozone levels ever observed in the atmosphere.

At Kilauea Volcano, the recent effusive eruption of about 0.0005km3/day (500,000 m3) of basalt magma releases about 2,000 tonnes of sulfur dioxide into the lower troposphere. Downwind from the vent, acid rain and air pollution is a persistent health problem in Hawaii when the volcano is erupting. These large explosive eruptions would also inject a tremendous volume of sulfur aerosols into the stratosphere can lead to lower surface temperatures and promote depletion of the Earth's ozone layer.


There are also industrial production of SO2, including the following few.

Burning of fuels

Large amounts of coal and petroleum are burnt around the world in power stations to generate electricity and in industries to provide energy. Both types of fuels contain sulfur as an impurity, although coal contains a higher concentration of it. Diesel fuel, which is used in vehicles, also contains a little sulfur. It is estimated that 70% of worldwide atmospheric SO2 comes from power stations.

When these fuels are burnt, the sulfur undergoes oxidization to become sulfur dioxide. The chemical equation is as follows:

S (s) + O2 (g) --> SO2 (g)
*Sulfur is from fuel, while oxygen is from the air.

Oil refining:
Sulfur and hydrogen sulfide are constituents of crude oil and H2S is released as a gas during catalytic cracking. Since H2S is considerably more toxic than SO2 it is burned to produce SO2 before release to the ambient air.

Pulp and paper manufacture: 
The sulfite process for wood pulping uses hot H2SO3 and thus emits SO2 in air. The kraft pulping process produces H2S, which is then burned to produce SO2.