04/12/011 The contribution of Earth degassing to the atmospheric sulfur budget By Hans-F. Graf, Baerbel Langmann, Johann Feichter From Chemical Geology 147, 1998, 131~ Woon-sup Choi

04/12/012 Introduction Cataclysmic eruptions inject large amounts of sulfur gases (SO 2 ) into the atmosphere  oxidized and form sulfate (SO 4 2- ) 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 SO 2 fluxes due to the incomplete knowledge of the global state of volcanic activity An exception: Mt. Etna  6-monthly periodicity of SO 2 degassing in relation to the 6-monthly Earth tide

04/12/013 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

04/12/014 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 SourceEmission (TgS/yr) Anthropogenic78.1 Volcanic14±6 Oceanic (DMS)15.4 Terrestrial0.4 Biomass2.2

04/12/015 Data and model (cont’d) Regional data Observations at Mt. Etna Full line: monitoring data, dotted line: 10-yr mean emissions (1975~85)

04/12/016 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 SO 2 /day With additional 4,000t SO 2 /day and 20,000t SO 2 /day released from the summit level of Mt. Etna

04/12/017 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

04/12/018 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 SO 4 2-  more efficient sulfate production

04/12/019 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

04/12/0110 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

04/12/0111 Results (cont’d) Radiative forcing (table 2) Significant seasonal difference SO 2 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

04/12/0112 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 4000tSO 2 emissions/day The contribution of Mt. Etna effects to the European sulfate burden, radiative forcing and total sulfur deposition increase nearly linearly with increasing SO 2 emissions at Mt. Etna Only southern Europe is significantly influenced by Mt. Etna emission

04/12/0113 Conclusions Volcanoes mainly inject SO 2 H 2 S 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