The irritant gas with the chemical formula SO₂ is non-flammable and has the property of solidifying into a colourless liquid at -10 °C. It is also easily soluble in water (sulphurous acid) and three times heavier than air. It is also easily soluble in water (sulphurous acid) and is two to three times heavier than air.
Under the designation E 220, sulphur dioxide is used in the food industry as a preservative, disinfectant and antioxidant, e.g. in wine, fruit juices, dried fruits and jams. Since SO₂ has the property of destroying vitamin B12, it must not be used, or only to a limited extent, in the production of meat products, dairy or cereal products.
In addition, sulphur dioxide is used in the production 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 protective gas, e.g. for metal melting in foundries.
In order to protect health, binding limit values for sulphur dioxide were set throughout Europe in 2005. The now valid one-hour limit value of 350 µg/m³ may be exceeded no more than 24 times a year. The daily limit value is an SO₂ concentration of 125 µg/m³, which may only be exceeded up to three times in a year. In addition, an alarm threshold of 500 µg/m³ applies to sulphur dioxide. If this value is measured in three consecutive hours at different locations representative for the area, the respective member state is obliged to take appropriate measures immediately.
According to the German Hazardous Substances Ordinance, a concentration of 2.5 mg/m³ (1 ppm) has been set as the workplace limit value for sulphur dioxide. This is derived from the value for the maximum workplace concentration (MAK value), which is 1 ml/m³ or 2.7 mg/m³.
Furthermore, it should be noted that SO₂ pollution increases at low temperatures and the associated increase in emissions caused by heating-related combustion processes. Due to the restricted air exchange, sulphur dioxide levels also increase during inversion weather conditions.
If sulphur dioxide oxidises in the atmosphere, this can lead to "acid rain", i.e. precipitation with a pH value between 4.2 and 4.8, which can cause lasting damage to the ecosystem, buildings and materials.
As a strong respiratory poison, SO₂ can cause coughing, shortness of breath or inflammation of the respiratory tract and mucous membranes as well as eye irritation even at a concentration of 0.04 % in the air. Furthermore, sulphur dioxide dissolved in water can corrode the stomach walls if ingested orally.
If the MAK value of sulphur dioxide is exceeded, headaches, nausea and drowsiness can be the result. If one is exposed to high SO₂ concentrations over a longer period of time, blood formation is impeded by the destruction of vitamin B12, which can result in anaemia.
Lungs and bronchial tubes are also damaged by high sulphur dioxide exposure. Asthmatics and patients with other chronic lung conditions are therefore particularly affected by high SO₂ levels.
Some fossil fuels, such as coal or various petroleum products, contain up to 4 % sulphur. When these are burnt, sulphur dioxide is produced, among other things. Active volcanoes also produce SO₂.
In addition, sulphur dioxide is emitted by various means of transport, with international shipping being one of the largest SO₂ emitters. Other sources of sulphur dioxide emissions also include energy and heat generation plants in industry, but also domestic fires. Sulphur dioxide is also released during the production of cement and pulp and the processing of ores and petroleum.
Sulphur dioxide is measured by means of an electrochemical sensor. SO₂ molecules that "dock" on the surface of the sensor cause a small current in the sensor. The advantage of our sensor is the individual sensitivity calibration by the manufacturer and the particularly long service life. The disadvantage of electrochemical SO₂ sensors is strong cross-sensitivities.
The sensor we use has a strong cross-sensitivity to hydrogen sulphide (H₂S) and nitrogen monoxide (NO) as well as to ozone (O₃) and alcohols. It therefore also reacts to H₂S and NO and then shows a rash, even if no SO₂ is present. It reacts negatively to O₃ and alcohols. If O₃ or alcohols increase, the measured SO₂ value decreases. These cross-sensitivities can also be evaluated and used to improve the measurement results.
The air-Q is a measuring device for sulphur dioxide and indoor air and can be ordered in the shop.