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Sulfur Dioxide (SO2) is an important trace species in the atmosphere, both under background conditions and in polluted areas. It is released to the troposphere as a result of both anthropogenic and natural phenomena.

Only one-quarter of the sulfur in the atmosphere is natural , and the rest is caused by human activities. (see Figure)

atmospheric_so2_cycle_small (12K)

This figure sketches the atmospheric SO2 cycle and contribution from both anthopogenic and natural sources...

The main sources of sulfur dioxide include:
  • Fossil fuel consumptions

  • The smelting of metal sulfide ores to obtain the pure metals.metals such as zinc, nickel, and copper are all commonly obtained in this manner

  • Coal burning - coal typically contains 2-3 % sulfur so when it is burned sulfur dioxide is liberated.

  • Organic decay - (Oxidation of organic material in soils, di methylsulfide (DMS) and H2S over oceans, and biomass burning.)

  • Volcanic eruptions - although this is not a wide spread problem, a volcanic eruption can add very large amount of sulfur dioxide to the atmosphere in a regional area. In special cases the volcanic plume can even reach the stratosphere.

  • Acid Rain

so2_emission_sources_small (23K)

This figure shows the both anthropogenic and natural sources of atmospheric so2

Chemistry of SO2 in the Atmosphere

SO2 reacts rapidly with OH to form HSO3, which reacts with O2 to form SO3. It is soluble in clouds and aerosols, where it reacts with H2O2. As a result of these processes, SO2 is converted to H2SO4 it causes Acid rain and deforestation.
In general the maximum Concentration of SO2 is close to its source and the amount of SO2 decreases rapidly as the distance from the source increases, indicating a short tropospheric lifetime of typically a few days.

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The important trace gas ozone is GOME's primary target species. However, the column amounts of a number of important atmospheric trace gases which have comparably weak atmospheric absorptions, among them SO2, can also be retrieved. SO2 column densities are derived from the near-UV GOME radiance / irradiance measurements by a differential optical absorption spectroscopy (DOAS) algorithm [Platt et al., 1994, Wagner et al., (WIT), Richter et al., 1998a, b] similar to that employed for ground-based zenith-sky measurements.

Our own Algorithm developed locally at the Institute of Environmental Physics, University of Heidelberg Germany, is based on the above mentioned DOAS techniques. The wavelength window 312.5 - 327.60 nm containing 122 detector pixels has been selected for the SO2 analysis and was found best optimum for the retrieval of SO2 column densities.

The absorption signature of the ozone Huggins bands, which is typically one to two order of magnitude larger than the SO2 absorptions, has been subtracted from the measured optical density, the SO2 absorptions then can be clearly identified in the satellite measured spectra.

so2_DAOS__fit_small (7K)

Figure shows the Spectral analysis of an atmospheric GOME measurement with respect to SO2.

The SO2 absorption structure ( black curve) can be clearly identified (the red curve represents an SO2 absorption spectrum taken in the laboratory. (The Ring spectrum is included in the analysis to correct for Raman scattering.)


IUP Bremen daily (level-2) SO2 NRT data-product.
Global SO2 maps by TOMS.
Global surface seawater DMS data base.
Coal fires in china.


Platt U., "Differential optical absorption spectroscopy (DOAS)", in Air Monitoring by Spectroscopic Techniques. Chem. Anal. Ser., 127, 27-84, 1994

J. P. Burrows et al., The Global Ozone Monitoring Experiment (GOME): Mission Concept and First Scientific Results, vol. 56(2), pp. 151-175, 1999.

Eisinger, M., and J. P. Burrows, Tropospheric Sulfur Dioxide observed by the ERS-2 GOME Instrument. . Journal of Atmospheric sciences, , No. 25, pp. 4177-4180, 1998. Geo phys. Res. Letter, 1995.

Read, W. G., L. Froidevaux, and J. W. Waters, 1993: Microwave limb sounder measurement of stratospheric SO2 from the Mt. Pinatubo volcano. Geophys. Res. Lett., 20, 1299-1302.

Boucher et al.:2003; Sensitivity of atmospheric sulphur to DMS flux and oxidation, Atoms. Chem. Phys., 3, 49-65, 2003

Richter, A., M. Eisinger, A. Ladstätter-Wei_enmayer, and J. P. Burrows, DOAS zenith sky observations. 2. Seasonal variation of BrO over Bremen (53_N) 1994{1995, J. Atm. Chem.,in press, 1998a.

Wagner, T., K. Chance, U. Frieß, M. Gil, F. Goutail, G. Hönninger, P.V. Johnston, K. Karlsen-Tornkvist, I. Kostadinov, H. Leser, A. Petritoli, A. Richter, M. Van Roozendael, U. Platt, Correction of the Ring effect and I0-effect for DOAS observations of scattered sunlight Proc. of the 1st DOAS Workshop, Heidelberg, 13., 14. Sept., Heidelberg, Germany, 2001.