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Jai Ganesh

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Registered: 2005-06-28

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Re: Miscellany

2525) Sulfur Dioxide

Gist

Sulfur dioxide (SO2) is a colorless, pungent, and toxic gas composed of sulfur and oxygen, primarily produced by burning fossil fuels and volcanic activity. It is a major air pollutant known to cause respiratory issues, such as difficulty breathing and asthma exacerbation. Industrially, it is crucial for manufacturing sulfuric acid and used as a preservative in food and wine.

Sulfur dioxide (SO2) is an industrial chemical used primarily as a precursor for sulfuric acid production, a preservative (especially for dried fruits and wine), a bleaching agent in paper/pulp manufacturing, and a disinfectant. It acts as a reducing agent in chemical processes and a refrigerant in industrial cooling systems.

Summary

Sulfur dioxide (SO2), is an inorganic compound, a heavy, colorless, poisonous gas. It is produced in huge quantities in intermediate steps of sulfuric acid manufacture.

Sulfur dioxide has a pungent, irritating odor, familiar as the smell of a just-struck match. Occurring in nature in volcanic gases and in solution in the waters of some warm springs, sulfur dioxide usually is prepared industrially by the burning in air or oxygen of sulfur or such compounds of sulfur as iron pyrite or copper pyrite. Large quantities of sulfur dioxide are formed in the combustion of sulfur-containing fuels.

Sulfur dioxide pollution carries serious health and environmental risks and is one of the six criteria air pollutants regulated by the U.S. Environmental Protection Agency and other regulatory agencies around the world. In the atmosphere sulfur dioxide can combine with water vapor to form sulfuric acid, a major component of acid rain; in the second half of the 20th century, measures to control acid rain were widely adopted. Most of the sulfur dioxide released into the environment comes from coal-fired power plants and petroleum refineries. Paper pulp manufacturing, cement manufacturing, and metal smelting and processing facilities are other important sources.

Sulfur dioxide is a precursor of the trioxide (SO3) used to make sulfuric acid. In the laboratory the gas may be prepared by reducing sulfuric acid (H2SO4) to sulfurous acid (H2SO3), which decomposes into water and sulfur dioxide, or by treating sulfites (salts of sulfurous acid) with strong acids, such as hydrochloric acid, again forming sulfurous acid.

Details

Sulfur dioxide (SO2) is a pungent, toxic gas that is the primary product of burning elemental sulfur. It exists widely in nature, mostly from volcanic activity and burning fossil fuels. It is found elsewhere in the solar system, as a gas in the atmospheres of Venus and Jupiter’s moon Io and as an ice on the other Galilean moons.

The major use of SO2 is in the manufacture of sulfuric acid (H2SO4), the most-produced chemical worldwide. Elemental sulfur and oxygen react to form SO2, which is catalytically oxidized with additional oxygen to make sulfur trioxide (SO3). The SO3 is mixed with existing H2SO4 to produce oleum (fuming sulfuric acid), which is added to water in a strongly exothermic process to make concentrated H2SO4. This is known as the contact process; it dates to an 1831 patent by British inventor Peregrine Phillips.

In chemical laboratories, it has multiple functions, including as a reducing agent, as a reagent in sulfonylation reactions, and as a low-temperature solvent. SO2 is also used to preserve dried fruits such as raisins and prunes and to prevent spoilage in wine.

The hazard information table shows that SO2 is pretty nasty stuff; but, in addition to its value as a chemical, it has another positive side: Volcanoes that emit the gas can have a beneficial effect on climate change. When SO2 spews into the stratosphere, it reacts photochemically with oxygen to form H2SO4 aerosols, which in turn reflect solar radiation and cool the atmosphere. But, as might be expected, even this has a downside because SO2 and H2SO4 contribute to acid rain.

Additional Information:

What Is Sulfur Dioxide?

Sulfur dioxide (SO2) is a gaseous air pollutant composed of sulfur and oxygen. SO2 forms when sulfur-containing fuel such as coal, petroleum oil, or diesel is burned. Sulfur dioxide gas can also change chemically into sulfate particles in the atmosphere, a major part of fine particle pollution, which can blow hundreds of miles away.

What Are the Health Effects of Sulfur Dioxide Pollution?

Sulfur dioxide causes a range of harmful effects on the lungs:

* Wheezing, shortness of breath and chest tightness and other problems, especially during exercise or physical activity. Rapid breathing during exercise helps SO2 reach the lower respiratory tract, as does breathing through the mouth.
* Long-term exposure at high levels increases respiratory symptoms and reduces the ability of the lungs to function.
* Short exposures to peak levels of SO2 in the air can make it difficult for people with asthma to breathe when they are active outdoors.
* Increased risk of hospital admissions or emergency room visits, especially among children, older adults and people with asthma.

What Are the Sources of Sulfur Dioxide Emissions?

As of 2020, human-made sources in the U.S. emit about 1.8 million short tons of sulfur dioxide per year (down from just over 6 million short tons per year in 2011) mainly from burning fuels. Power plants, commercial and institutional boilers, internal combustion engines, manufacturing, and industrial processes such as petroleum refining and metal processing are the largest sources of emissions, followed by diesel engines in old buses and trucks, locomotives, ships, and off-road equipment such as construction vehicles. Emissions of sulfur dioxide will decline as cleanup of many of these sources continue in future years.

Where Do High SO2 Concentrations Occur?

Coal-fired power plants remain one of the biggest sources of sulfur dioxide in the U.S. Columns of emissions (plumes) such as from chimneys of a coal-fired power plant are moved by wind over long distances before touching down at ground level at far away sites. These plumes could also get trapped at the ground level by unusual weather conditions such as a layer of warmer air occurring higher up in the atmosphere (inversion).

Ports, smelters, and other sources of sulfur dioxide also cause high concentrations of emissions nearby.

People who live and work near these large sources get the highest exposure to SO2.

What Can We Do about it?

SO2 levels have improved over time, thanks to policies requiring cleaner fuels and pollution controls on power plants. The nation achieved major reductions in this pollutant through its successful program to reduce acid rain.

However, it remains a health concern. What’s more, even with pollution controls installed, high levels can occur when a polluting source such as a power plant is starting up or shutting down its operation or if its equipment malfunctions.

Individuals can take steps to protect themselves on days with unhealthy levels of air pollutants and also ask policymakers at all levels of government to continue to require cleanup of air pollution.

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