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Home > The ABC of air > Pollutants
Sulphur dioxide (SO2)

The sources

Sulphur dioxide (SO2) is emitted during the combustion of fossil fuels such as coal and fuel oil. The main sources are power plants, large industrial combustion plants and heating units, (both individually and collectively) and sea and river transport.  SO2 emissions have reduced significantly because of technical and regulatory measures that have been taken, because of reducing consumption of fuel oil and high sulphur coals, and the important role of nuclear energy.

The emissions inventory provides information as to the origins of the majority of the SO2, from above all the industrial sector (89.5 %), and particularly oil refining as well as the thermal power plant at Le Havre and several chemical industries. Sea and river transport is on the second range with 7 % in 2005.

Health effects

Le SO2 is an irritant of the mucous membranes, skin and upper respiratory tract (coughing, difficulty breathing). It works in synergy with other substances, notably with fine particles. Like all the pollutants, its effects are exacerbated by smoking.

Effects on the environment

SO2 is transformed into sulphuric acid on contact with moisture in the air and contributes to the phenomenon of acid rain. It also contributes to the degradation of stone and materials of numerous monuments.

The reference standards

Information and recommendation threshold for sensitive individuals Alert warning threshold for the general population
300 µg/m3 hourly average 500 µg/m3 hourly average, over 3 consecutive hours

In Upper Normandy, these thresholds are governed by the Prefectural by-law of 20th July 2007.

Air quality objective
50 µg/m3 annual  average
Limit values for the protection of human health
hourly average daily average
350 µg/m3 not to be exceeded more than 24 hours per year 125 µg/m3 not to be exceeded more 3 days per year
Limit values for the protection of ecosystems
annual  average average from October 1st to March 31st
20 µg/m3 20 µg/m3