Sulfur dioxide (general characteristics)
Under normal conditions, it is a colorless gas with a characteristic pungent odor (the smell of a lighted match). It liquefies under pressure at room temperature. It dissolves in water to form unstable sulfurous acid. It also dissolves in ethanol and sulfuric acid. One of the main components of volcanic gases.
Sulfur dioxide, which is one of the most harmful components of pollution, accumulates in the atmosphere as a result of the processing and combustion of organic substances (hard and brown coal, oil, oil products, wood), the production and use of sulfuric acid, and the smelting of sulfur-containing ores. It is emitted by thermal power plants, ferrous and non-ferrous metallurgy enterprises, coke and cement plants, factories for the production of synthetic fibers, ammonia, and cellulose.
In industrial areas, the concentration of sulfur dioxide usually reaches 0.05–0.1 mg/m3; in rural areas it is several times less, and over the ocean it is 10–100 times less. In rural areas, the background concentration is close to 0.5 µg/m 3 , while the concentration in urban areas is 50-100 times higher. Due to chemical transformations, the lifetime of sulfur dioxide in the atmosphere is short (on the order of several hours). In this regard, the possibility of pollution and the danger of exposure directly to sulfur dioxide are, as a rule, local, and in some cases regional in nature.
According to 1978 data, 110 million tons of sulfur dioxide entered the atmosphere annually, of which 75% came from North America and Western Europe. The increase in sulfur dioxide emissions in recent years is a direct consequence of the shortage of energy resources. Previously, when it was not yet felt, high-sulfur coals and fuel oils were almost never used as fuel. However, now they are actively burned and serve as one of the main causes of air pollution.
Chemical methods for the determination of sulfur dioxide in atmospheric air
2.1 Ultraviolet fluorescent method for measuring the content of sulfur dioxide in atmospheric air using automatic gas analyzers.
This International Standard is applicable to the determination of the mass concentration of sulfur dioxide in the range from a few micrograms per cubic meter to a few milligrams per cubic meter.
The gas analyzer readings are affected by ambient temperature and atmospheric pressure. Compared to other currently used methods, this method has less effect of interfering chemicals on the measurement result. However, the accuracy of determining the content of ESODVA can be affected by: hydrogen sulfide, aromatic hydrocarbons, nitric oxide, water. In cases where various pollutants are present in the air in large quantities, it is recommended to determine their effect on the output signal of the gas analyzer.
The ultraviolet fluorescence method is based on the fluorescence emission of light by SO2 molecules previously excited by UV radiation.
2.2 The method is based on the capture of sulfur dioxide from the air by a film sorbent or absorbent solution, its oxidation to sulfate ions and their spectrophotometric (turbidimetric) determination by turbidity as a result of the interaction of sulfate ions with barium chloride; the cloudiness intensity is proportional to the concentration of sulfur dioxide.
Bioindication of sulfur dioxide
Effect of sulfur dioxide on living organisms and bioindication.
The impact of sulfur dioxide and its derivatives on humans and animals is manifested primarily in the defeat of the upper respiratory tract. Sulfur dioxide can disrupt carbohydrate and protein metabolism, reduce the body’s resistance to infectious agents. Under the influence of sulfur dioxide and sulfuric acid, photosynthesis and respiration deteriorate, the level of carbon dioxide increases, growth slows down, the quality of tree plantations and crop yields decrease, and at higher doses of exposure, vegetation dies.
In botany, among the organisms that can be used to detect specific pollution of the air basin and to monitor the dynamics of this pollution, include lower plants, lichens, fungi, and many higher plants.
Effect of sulfur dioxide on living organisms at the cellular and subcellular levels.
Effect of sulfur dioxide on biomembranes. Sulfur dioxide penetrates the leaf through the stomata, enters the intercellular space, dissolves in water with the formation of SO 3 2- /HSO 3 – ions that destroy the cell membrane. As a result, the buffer capacity of the cell cytoplasm decreases, its acidity and redox potential change.
The action of sulfur dioxide on enzymes affects the process of normal attachment of the enzyme to the substrate. As a result, various processes are disrupted, for example:
The assimilation of carbon dioxide during photosynthesis.
Interaction of SO 2 with HS-groups of proteins, which leads to the destruction of enzymes
Certain protective substances accumulate in plant cells under the influence of various contaminants. Bioindication of SO 2 is associated with the determination of the concentration of this substance in plants:
§ proline – an amino acid considered an indicator of stress;
§ alanine – an amino acid accumulated in the cells of trebo-uxia algae, pine and corn when contaminated;
§ Peroxidase and superoxide dismutase.
When contaminated in plant cells, the following changes in pigments occur:
ü the content of chlorophyll decreases;
ü the ratio of chlorophyll a / chlorophyll b decreases;
ü chlorophyll fluorescence slows down.
With pollution, the concentration of soluble proteins in cells decreases. Gas emissions lead to a decrease in the content of myristic, palmitic and lauric acids and to an increase in linoleic and linolenic acids in the composition of lipids.
It is shown that in case of gas-smoke pollution:
Ø cells of resin passages in coniferous trees increase;
Ø the cells of the epidermis of the leaves are reduced.
In the zone of air pollution with sulfur dioxide, plants intensively accumulate sulfur in their tissues. Usually, the higher the content of this element in plants, the more pronounced the damage to the leaves. First, burns occur on them, then the leaf blades wrinkle, die off and fall off. At a concentration of sulfur dioxide of the order of 1:1,000,000, pine needles fall off. If the concentration increases, the needles may die in a few hours.
Conifers are particularly affected by sulfur dioxide. As you know, the life expectancy of pine needles under normal conditions is 3-4 years. During this time, it accumulates such an amount of sulfur dioxide that significantly exceeds the threshold value. Under the influence of a toxicant, pine needles in heavily polluted areas acquire a dark red color, which spreads from the base of the needle to its tip, and then dies and falls off, having existed for only one year.
According to Gertel’s observations, the thickness of the wax layer on pine needles is the greater, the higher the concentration or the longer exposure to sulfur dioxide. This circumstance served as the basis for the development of a quantitative method for indicating this compound in the atmosphere. The essence of the method is that a certain amount of needles is boiled in water. It is assumed that the degree of turbidity of the extract is directly proportional to the amount of wax covering the needles. The higher the turbidity, set using instruments, the greater the concentration of sulfur dioxide in the air. This method is called the “Hertel haze test”.
Further studies showed, however, that clouding of the water extract from the needles is caused not only by wax, but also by a number of other substances present in plant tissues.
Meanwhile, the accumulation of epicuticular wax under the influence of sulfur dioxide was found not only in conifers, but also in other plants. For this reason, it may be necessary to determine not the intensity of the turbidity of the extract, but directly the content of wax in the plant material.