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Sulphur dioxide in the atmosphere

DOAS SO2 retrievals

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page last modified:
Mon 23 June 2003

 

 

 



This SO2 website now features GOME and SCIAMACHY!

Sulphur Dioxide in the atmosphere

Sulphur dioxide, SO2, enters the atmosphere as a result of both natural phenomena and anthropogenic activities, such as:

  • Combustion of fossil fuels
  • Oxidation of organic material in soils
  • Volcanic eruptions
  • Biomass burning

Coal burning is the single largest man-made source of sulphur dioxide, accounting for about 50% of annual global emissions, with oil burning accounting for a further 25 to 30%. Sulphur dioxide reacts on the surface of a variety of airborne solid particles (aerosols), is soluble in water and can be oxidised within airborne water droplets, producing sulphuric acid. This acidic pollution can be transported by wind over many hundreds of kilometres, and is deposited as acid rain.

Changes in the abundance of sulphur dioxide have an impact on atmospheric chemistry and on the radiation field, and hence on the climate. Consequently, global observations of sulphur dioxide are important for atmospheric and climate research.

Effects of volcanic eruptions may have an impact on air traffic, as such eruptions are important sources of ash (aerosols) and sulphur dioxide in the atmosphere. A near-real time retrieval of sulphur dioxide concentrations would enable monitoring of such events and can thus assist in aviation control. Off-line retrieval, on the other hand, is more suitable for monitoring anthropogenic pollution aspects.


Volcano eruptions

Volcano eruptions, for example, are important sources of gases in the atmosphere, but:

  • emissions are sporadic and intermittent;
  • emissions often occur in uninhabited regions.
In-situ assessment of emissions is therefore difficult or even impossible. Observations of sulphur dioxide from space provides important information to earth scientists.

Eisinger & Burrows have shown that the retrieval of sulphur dioxide from GOME spectra is possible with a Differential Optical Absorption Spectroscopy (DOAS) technique.


Sulphur dioxide in troposphere and stratosphere

The lifetime of sulphur dioxide molecules in the troposphere is a few days. The amount is highly variable, above a low background concentration.

It is removed from the troposphere :

  • in gas phase by formation of sulphuric acid, which forms condensation nuclei for aerosols and clouds and acidifies the rain;
  • directly, by way of an uptake on aerosols and clouds, which leads to dry and wet acid depositions.

Clean continental air contains less than 1 ppb of sulphur dioxide, which corresponds to a total column density < 0.2 Dobson Units (DU) in a boundary layer of 2 km.

The lifetime of sulphur dioxide molecules in the stratosphere, on the other hand, is several weeks, during which is produces sulphate aerosols. This makes sulphur dioxide from volcanos one of the two most important sources of stratospheric aerosols.

Reference

Eisinger, M., and J. P. Burrows, Tropospheric Sulfur Dioxide observed by the ERS-2 GOME Instrument, Geophys. Res. Lett., No. 25, pp. 4177-4180, 1998.


Last updated : Mon 23 June 2003
Data product contacts : Isabelle De Smedt, Nicolas Theys, Michel Van Roozendael
Acknowledgements: Pascal Blonde (Paris Observatory), Jean-Louis Piette, Sayid Azim (AP), Graphic Maps/Worldatlas.com, IGPN and USGS
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