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The contribution of Earth degassing to the atmospheric sulfur budget

The contribution of Earth degassing to the atmospheric sulfur budget. By Hans-F. Graf, Baerbel Langmann, Johann Feichter From Chemical Geology 147, 1998, 131~145 04-12-01 Woon-sup Choi. Introduction.

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The contribution of Earth degassing to the atmospheric sulfur budget

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  1. The contribution of Earth degassing to the atmospheric sulfur budget By Hans-F. Graf, Baerbel Langmann, Johann Feichter From Chemical Geology 147, 1998, 131~145 04-12-01 Woon-sup Choi

  2. Introduction • Cataclysmic eruptions inject large amounts of sulfur gases (SO2) into the atmosphere  oxidized and form sulfate (SO42-) aerosols • Backscatter of solar radiation and Modification of heating of atmospheric layers  counteraction to anthropogenic greenhouse effect • Great difficulty in constraining even the magnitude of SO2 fluxes due to the incomplete knowledge of the global state of volcanic activity • An exception: Mt. Etna  6-monthly periodicity of SO2 degassing in relation to the 6-monthly Earth tide

  3. Introduction (cont’d) • Purpose of study • To investigate the relative contribution of tropospheric sulfur emissions from volcanic vs. anthropogenic and biogenic sources • To study the sulfate budgets and the radiative forcing for all source types separately • To examine the regional effects of a specific source (Mt. Etna on Sicily) for different observed emission rate during one winter episode

  4. Data and model • Global data • Global sulfur sources estimate (table 1) • Spatial distribution of volcanic emissions by Bates et al.(1987) with proportional addition of the higher emission values resulting from our global estimate

  5. Data and model (cont’d) • Regional data • Observations at Mt. Etna • Full line: monitoring data, dotted line: 10-yr mean emissions (1975~85)

  6. Data and model (cont’d) • Combination of the regional circulation model HIRHAM and Chemistry-Transport-Model (CTM) • For treatment of the liquid water content of clouds and the fractional cloud cover as prognostic variables • Run for one winter episode (Jan 13~23, 1991) with three different emission values in the area • With anthropogenic emissions of 700t SO2/day • With additional 4,000t SO2/day and 20,000t SO2/day released from the summit level of Mt. Etna

  7. Data and model (cont’d) • ECHAM4 • Atmospheric global circulation model • 3.75° horizontal resolution with 19 vertical layers • Up to atmospheric top at 10hPa • Combined with simpler sulfur chemistry module

  8. Results • Global model calculations • Global vertical distribution • Anthropogenic sulfate is found with a total mass of 0.29TgS in Jan: slightly more than volcanic and DMS • Volcanic sulfate (0.35TgS) is almost twice as high as DMS and slightly higher than the anthropogenic sulfate in July • In summer, faster oxidation of SO2 to SO42- more efficient sulfate production

  9. Results (cont’d) • Global vertical distribution (cont’d) • Anthropogenic sulfate: dominant in the lower and middle troposphere • DMS: dominant in high altitude (above 10km)  Not deposited in the model at the surface, neither by dry nor wet processes • Volcanic sulfate: dominant in mid-high altitude (above 5km), and significant seasonal variation

  10. Results (cont’d) • Tropical vertical distribution • No large seasonal difference • Volcanic is most abundant in the vertical column • Biomass burning is still negligible • DMS can be transported vertically in the strong tropical uplifts  DMS and volcanic sources are equally important in the uppermost troposphere and in the stratosphere

  11. Results (cont’d) • Radiative forcing (table 2) • Significant seasonal difference • SO2 emission from anthropogenic sources is stronger in winter  delay of the oxidation into sulfate and the efficient wet deposition of sulfate  reduction of the atmospheric lifetime of radiatively active sulfate

  12. Results (cont’d) • Regional model studies-- Mt. Etna • The continuous degassing contributes more to the sulfur burden of the atmosphere than do its few explosive events • 4000t/day of addition  only local effects in the episodic mean. However, looking at daily mean values, the influence of Mt. Etna emissions covers greater areas • 20,000t/day of emission  enhancement by a factor of about 4.5 in comparison to 4000tSO2 emissions/day • The contribution of Mt. Etna effects to the European sulfate burden, radiative forcing and total sulfur deposition increase nearly linearly with increasing SO2 emissions at Mt. Etna • Only southern Europe is significantly influenced by Mt. Etna emission

  13. Conclusions • Volcanoes mainly inject SO2 H2S into the free troposphere, while anthropogenic sources remain in the planetary boundary layer, where removal processes are very efficient • Single point strong emissions, like from Mt. Etna, have only regional effects. • However, they can lead to sulfur burden in rural areas, which is comparable to that of highly industrialized area • There is urgent need to better understand and monitor the natural emissions of volcanic gases and their time-space variability

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