Sulfur dioxide (SO₂)

Description:

This irritant gas, with the chemical formula SO₂, is nonflammable and solidifies into a colorless liquid at -10 °C. It is also readily soluble in water (sulfurous acid) and is two to three times heavier than air.

Under the designation E 220, sulfur dioxide is used in the food industry as a preservative, disinfectant, and antioxidant—for example, in wine, fruit juices, dried fruits, and jams. Since SO₂ has the property of destroying vitamin B12, it cannot be used—or can only be used to a limited extent—in the production of meat, dairy, or grain products.

In addition, sulfur dioxide is used in the manufacture of various chemicals, medicines, cosmetics, and dyes. It is also used as a solvent and in the bleaching of paper and textiles, and serves as a shielding gas, for example in the smelting of metals at foundries.

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Sulfur dioxide limit values:

To protect public health, binding limit values for sulfur dioxide were established at the European level in 2005. The hourly limit value currently in effect—350 µg/m³—may not be exceeded more than 24 times per year. The daily limit value is set at a sulfur dioxide concentration of 125 µg/m³, which may be exceeded no more than three times per year. In addition, an alert threshold of 500 µg/m³ applies to sulfur dioxide. If this value is measured for three consecutive hours at several representative locations in the area, the relevant Member State is required to take appropriate measures immediately.

According to the German regulation on hazardous substances, an occupational exposure limit of 2.5 mg/m³ (1 ppm) has been set for sulfur dioxide. This is derived from the maximum workplace concentration (MAK value), which is 1 ml/m³ or 2.7 mg/m³.

In addition, it should be noted that SO₂ concentrations increase at low temperatures due to higher emissions from heating combustion processes. Sulfur dioxide levels also rise during temperature inversion events due to limited air exchange.

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Consequences of a concentration that is too high:

If sulfur dioxide oxidizes in the atmosphere, it can cause “acid rain”—that is, precipitation with a pH between 4.2 and 4.8. This causes damage—some of it permanent—to the ecosystem, buildings, and materials.

As a potent respiratory toxin, SO₂ can, even at a concentration as low as 0.04% in the air, cause coughing, difficulty breathing, or inflammation of the respiratory tract and mucous membranes, as well as eye irritation. Sulfur dioxide dissolved in water can also corrode the stomach lining if ingested.

If the MAK value for sulfur dioxide is exceeded, it can cause headaches, nausea, and dizziness. Prolonged exposure to high concentrations of SO₂ can lead to the destruction of vitamin B12, which impairs blood formation and may result in anemia.

The lungs and bronchi are also damaged by high exposure to sulfur dioxide. As a result, people with asthma and other chronic lung diseases are particularly affected by high levels of SO₂.

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Sources of SO₂:

Some fossil fuels, such as coal and various petroleum products, contain up to 4% sulfur. When burned, they produce sulfur dioxide, among other substances. Active volcanoes also produce SO₂.

In addition, sulfur dioxide is emitted by various modes of transportation, with international maritime traffic being one of the largest sources of SO₂. Other sources of sulfur dioxide emissions include industrial power and heat generation facilities, as well as household fires. Sulfur dioxide is also released during the production of cement and cellulose, as well as in the processing of minerals and petroleum.

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Sensor used:

Sulfur dioxide is measured using an electrochemical sensor. SO₂ molecules that “adhere” to the sensor’s surface cause a small current to flow through the sensor. The advantage of our sensor is that the manufacturer individually calibrates its sensitivity, and it has an exceptionally long service life. The disadvantage of electrochemical SO₂ sensors is their high level of cross-sensitivity.

The sensor we use exhibits strong cross-sensitivity to hydrogen sulfide (H₂S) and nitrogen monoxide (NO), as well as to ozone (O₃) and alcohols. As a result, it also reacts to H₂S and NO, causing a deviation even when no SO₂ is present. It reacts negatively to O₃ and alcohols. When O₃ or alcohols increase, the measured SO₂ value decreases. These cross-sensitivities can also be evaluated and used to improve measurement results.

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Measure sulfur dioxide:

The air-⁠Q is a device for measuring sulfur dioxide and indoor air quality, and it can be ordered from the store.