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Sulphur dioxide (SO2)

Sulphur dioxide is a colourless gas with a pungent odour. In high concentrations it is very harmful to humans, flora and fauna. Fortunately, however, sulphur dioxide emissions are steadily decreasing.

Sulphur dioxide is released when fossil fuels such as oil and coal are burned. It has an irritating effect on mucous membranes and can thus be the cause of eye and respiratory problems. The particles also contribute to the formation of fine dust. The limit value for sulphur dioxide is 350 micrograms per cubic metre of air per hour. This value may be exceeded no more than 24 times a year. The daily value of 125 micrograms per cubic metre of air may be exceeded no more than three times a year.

However, concentrations of sulphur dioxide in Germany have now fallen to such an extent that the limit values are complied with and this substance hardly poses a threat to human health in this country. However, sulphur dioxide was involved in the acidification of soils. With the decline since the early 1990s, it is now nitrogen that is largely responsible for this.

Nowadays, it is mainly shipping traffic that emits the highest amount of sulphur dioxide. For ships sailing on the North Sea and Baltic Sea, the limit value for sulphur in fuel in some coastal zones is only 0.1 per cent. In other zones of these waters, the limit is slightly higher, at 0.5 per cent.  However, ships that cannot comply with these values have the option of cleaning their exhaust gases and washing out the sulphur dioxide. This so-called exhaust gas desulphurisation is also carried out on a large scale.

A study by the non-governmental organisation Transport & Environment shows how large the share of sulphur emissions from shipping is: in 2017, the cruise ships of the shipping company Carnival alone emitted as much sulphur dioxide as all 260 million passenger cars in Europe combined. This is a particular problem in the major ports, because sulphur dioxide promotes the formation of fine dust. Added to this is the condensation of air stimulated by sulphur dioxide and nitrogen oxide. This promotes cloud formation and hinders the removal of pollutants over the ports. No wonder, then, that the introduction of environmental zones in port areas as well is only a matter of time for many.