Sulfur dioxide is a colorless gas with a pungent odor that irritates skin and the tissues and mucous membranes of the eyes, nose, and throat. Sulfur dioxide chiefly affects upper respiratory tract and bronchi. Locally, sulfur dioxide gas can lead to acid rain and air pollution.
When sulfur is entrained in an aerosol, it is possible for sulfur oxides to reach far deeper into the lungs. The combination of particulate matter and sulfur oxides can then act synergistically, with the effects of both together being much more detrimental than either of them separately. Sulfur dioxide is one of the serious air pollutants which is responsible for smog formation, which has resulted in several incidents of loss of human lives. Atmospheric sulfur dioxide is harmful to plants and leaf tissue is killed with exposure to high levels of gas. A case study would further strengthen my point.
Case Study:
Linfen has been identified as one of its most polluted cities. Rapid development and unequivocal faith in industry has led to the development of hundreds of unregulated coal mines, steel factories and refineries which have polluted indiscriminately through the burning of fossil fuels, releasing soot, sulfur dioxide and excessive heat. The State Environmental Protection Administration (SEPA) has branded Linfen as having the worst air quality in the country. Levels of sulfur dioxide and other particulates are many times higher than limits set by the World Health Organization (WHO). Local clinics are seeing growing cases of bronchitis, pneumonia, and lung cancer. The children of Shanxi Province also have high rates of lead poisoning.
Sulfurous pollutants can discolour paint, corrode metals, and cause organic fibres to weaken. Airborne sulfates significantly reduce visibility and discolour the atmosphere. Prolonged exposure to sulfates causes serious damage to buildings made of marble, limestone and mortar, as the carbonates of these materials are replaced by sulfates, which are soluble in water.
CaCO3 +H2SO4→CaSO4 + CO2 +H2O
Furthermore, sulfur dioxide once released can convert to SO3, in a series of reaction which involve a free radical such as OH•. Sulfur trioxide react quickly with H2O to form sulfuric acid, which is the principal cause of acid rain.
SO3 + H2O → H2SO4
Sulfuric acid molecules rapidly become particles by either condensing on existing particles in the air or by merging with water vapour to form H2O - H2SO4 droplets. Often significant fraction of particulate matter in the atmosphere consist of such sulfate aerosols. The formation is promoted by the presence of hydrocarbons and nitrogen oxides, which are key components of photochemical smog. Photochemical smog is more harmful than the separate pollutants. It burns the eyes of people and is dangerous to people with breathing or heart problems. It is poisonous to plants, and damages materials such as paint and rubber.
In relatively humid atmospheres, SO2 is oxidized by reactions occurring inside water aerosol droplets, which proceed faster in the presence of ammonia and catalysts such as manganese (II), iron (II), nickel (II), copper (II), etc.
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