SO2 Mass Research Articles

On-Line Monitoring System for Monitoring SO<sub>2</sub> in Fumes（2） — Monitoring Subsystem for SO<sub>2</sub> Flow Velocity and Flow Rate

A SO2on-line monitoring system (CEMS) has been developed by the author based on the principle of electrochemistry. This system consists of SO2mass concentration monitoring subsystem (the subsystem had been described in on-line system for monitoring SO2in fumes（1）) and SO2flow velocity and flow rate monitoring subsystem. In the paper, the working principle and procedure of SO2flow velocity and flow rate monitoring subsystem are described in detail. In the meantime, an advanced method for measuring average flow velocity of fumes by mean of “velocity field constant” is presented. A innovative device has been developed to detect velocity field constants automatically, which has resolved the technical difficulty in automated monitoring of fumes average velocity in the flue.

Large scale modeling of the transport, chemical transformation and mass budget of the sulfur emitted during the April 2007 eruption of Piton de la Fournaise

Abstract. In April 2007, the Piton de la Fournaise volcano (Réunion island) entered into its biggest eruption recorded in the last century. Due to the absence of a sensors network in the vicinity of the volcano, an estimation of degassing during the paroxysmal phase of the event has not been performed. Nevertheless, the SO2 plume and aerosols have been observed by the OMI and CALIOP space sensors, respectively. The mesoscale chemical model MesoNH-C simulates the observed bulk mass of SO2 and the general shape of the SO2 plume spreading over the Indian Ocean. Moreover, an analysis of the SO2 plume budget estimates a total SO2 release of 230 kt, among of which 60 kt have been transformed into H2SO4. 27 kt of SO2 and 21 kt of H2SO4 have been deposited at the surface by dry deposition. With this top down approach, the temporal evolution of the SO2 emission has been estimated during the most active period of the eruption. The peak of degassing was estimated at 1800 kg s−1 in the morning of 6~April. The temporal evolution of SO2 emission presented here can also be used for local studies.

SO2 Adsorption on Carbon-Supported Pt Electrocatalysts

Adsorption of SO2 on a Pt/C catalyst typically used in proton exchange- membrane fuel cells (PEMFCs) has been investigated by temperature programmed desorption (TPD). SO2 concentrations in N2 were varied from 5 ppm to 1% (vol) and adsorption isotherms were determined at 25, 50, and 80 °C. Oxygen assisted (O-assisted) desorption experiments (i.e., successive TPD experiments following exposure to room temperature O2 after the first TPD event) produced an additional SO2 peak at a temperature higher than the initial SO2 peak. These two types of SO2 adsorption were identified as weakly adsorbed SO2 species desorbed between 140 and 200 °C, depending on concentration, and a strongly adsorbed, dissociated species. For the strongly adsorbed, dissociative species, (18)O2 isotope introduction during O-assisted desorption yielded ratios of 50%, 36%, and 14% for SO2 masses of 64, 66, and 68, respectively. The activation energy and kinetic constant of desorption are reported for weakly adsorbed SO2 at 1% and 20 ppm SO2 using the Polanyi-Wigner equation.

New clues on the contribution of Earth’s volcanism to the global mercury cycle

Active volcanoes are thought to be important contributors to the atmospheric mercury (Hg) budget, and this chemical element is one of the most harmful atmospheric pollutants, owing to its high toxicity and long residence time in ecosystems. There is, however, considerable uncertainty over the magnitude of the global volcanic Hg flux, since the existing data on volcanogenic Hg emissions are sparse and often ambiguous. In an attempt to extend the currently limited dataset on volcanogenic Hg emissions, we summarize the results of Hg flux measurements at seven active open-conduit volcanoes; Stromboli, Asama, Miyakejima, Montserrat, Ambrym, Yasur, and Nyiragongo.. Data from the dome-building Soufriere Hills volcano are also reported. Using our determined mercury to SO2 mass ratios in tandem with the simultaneously-determined SO2 emission rates, we estimate that the 7 volcanoes have Hg emission rates ranging from 0.2 to 18 t yr-1 (corresponding to a total Hg flux of ~41 t·yr-1). Based on our dataset and previous work, we propose that a Hg/SO2 plume ratio ~10-5 is best-representative of gas emissions from quiescent degassing volcanoes. Using this ratio, we infer a global volcanic Hg flux from persistent degassing of ~95 t·yr-1 .

Transport and evolution of a pollution plume from northern China: A satellite‐based case study

On 5 April 2005, during the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST‐AIRE) aircraft campaign, heavy loadings of SO2 (20 ppb near ground, 1–3 ppb at ∼2 km altitude) and dust with aerosol optical depth of ∼1 were measured over Shenyang, an industrialized city ∼600 km NE of Beijing. In this study, Ozone Monitoring Instrument (OMI) and MODIS satellite sensors are employed to look into this air pollution episode at a regional scale and to track the transport and evolution of the plume from China to the NW Pacific on the following days. A method is proposed to combine in situ measurements and trajectory tracer modeling with satellite observations to quantify the change in the SO2 mass during plume transport. We demonstrate that an air mass factor correction is needed for quantitative use of the OMI SO2 data, to account for the effects of the viewing geometry, the SO2 profile shape, and the aerosol/cloud interference on retrievals. The total SO2 loading of the plume decreased from ∼1.1 × 1011 g on 5 April to ∼5.0 × 1010 g on 7 April. The overall, e‐folding lifetime of SO2 in this plume, empirically derived from the rate of SO2 decay, was ∼2 days (range of 1–4 days). SO2 to sulfate conversion increased the aerosol optical depth by ∼0.1–0.4 near the center of the plume on 6 and 7 April, while the loss of primary dust particles reduced the aerosol loading of the plume by a similar amount. Simulations with a chemical transport model suggest similar loss of dust and formation of sulfate within the plume during transport. The method established in this study can be further developed and applied to study other episodes of pollution transport and their impact on weather and climate.

Dispersion and lifetime of the SO2 cloud from the August 2008 Kasatochi eruption

Hemispherical dispersion of the SO2 cloud from the August 2008 Kasatochi eruption is analyzed using satellite data from the Ozone Monitoring Instrument (OMI) and the Goddard Trajectory Model (GTM). The operational OMI retrievals underestimate the total SO2 mass by 20–30% on 8–11 August, as compared with more accurate offline Extended Iterative Spectral Fit (EISF) retrievals, but the error decreases with time due to plume dispersion and a drop in peak SO2 column densities. The GTM runs were initialized with and compared to the operational OMI SO2 data during early plume dispersion to constrain SO2 plume heights and eruption times. The most probable SO2 heights during initial dispersion are estimated to be 10–12 km, in agreement with direct height retrievals using EISF algorithm and IR measurements. Using these height constraints a forward GTM run was initialized on 11 August to compare with the month‐long Kasatochi SO2 cloud dispersion patterns. Predicted volcanic cloud locations generally agree with OMI observations, although some discrepancies were observed. Operational OMI SO2 burdens were refined using GTM‐predicted mass‐weighted probability density height distributions. The total refined SO2 mass was integrated over the Northern Hemisphere to place empirical constraints on the SO2 chemical decay rate. The resulting lower limit of the Kasatochi SO2 e‐folding time is ∼8–9 days. Extrapolation of the exponential decay back in time yields an initial erupted SO2 mass of ∼2.2 Tg on 8 August, twice as much as the measured mass on that day.

Remote sensing and inverse transport modeling of the Kasatochi eruption sulfur dioxide cloud

An analytical inversion method is used to estimate the vertical profile of sulfur dioxide (SO2) emissions from the major 2008 eruption of Kasatochi Volcano, located on the Aleutian Arc, Alaska. The method uses satellite‐observed total SO2 columns from the Global Ozone Monitoring Experiment‐2 (GOME‐2), Ozone Monitoring Instrument (OMI), and Atmospheric InfraRed Sounder (AIRS) during the first 2 days after the eruption, and an atmospheric transport model, FLEXPART, to calculate the vertical emission profile. The inversion yields an emission profile with two large emission maxima near 7 km above sea level (asl) and around 12 km asl, with smaller emissions up to 20 km. The total mass of SO2 injected into the atmosphere by the eruption is estimated to 1.7 Tg, with ∼1 Tg reaching the stratosphere (above 10 km asl). The estimated vertical emission profile is robust against changes of the assumed eruption time, meteorological input data, and satellite data used. Using the vertical emission profile, a simulation of the transport extending for 1 month after the eruption is performed. The simulated cloud agrees very well with SO2 columns observed by GOME‐2, OMI, and AIRS until 6 days after the eruption, and the altitudes agree with both Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation measurements and ground‐based lidar observations to within 1 km. The method is computationally very fast. It is therefore suitable for implementation within an operational environment, such as the Volcanic Ash Advisory Centers, to predict the threat posed by volcanic emissions for air traffic.

Volcanic ash and SO2 in the 2008 Kasatochi eruption: Retrievals comparison from different IR satellite sensors

The Kasatochi 2008 eruption was detected by several infrared satellite sensors including Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Very High Resolution Radiometer (AVHRR), and Atmospheric Infrared Sounder (AIRS). In this work a comparison between the volcanic cloud SO2 and ash retrievals derived from these instruments has been undertaken. The SO2 retrieval is carried out by using both the 7.3 and 8.7 μm absorption features while ash retrieval exploits the 10–12 μm atmospheric window. A radiative transfer scheme is also used to correct the volcanic ash effect on the 8.7 μm SO2 signature. As test cases, three near‐contemporary images for each sensor, collected during the first days of the eruption, have been analyzed. The results show that the volcanic SO2 and ash are simultaneously present and generally collocated. The MODIS and AVHRR total ash mass loadings are in good agreement and estimated to be about 0.5 Tg, while the AIRS retrievals are slightly lower and equal to about 0.3 Tg. The AIRS and MODIS 7.3 μm SO2 mass loadings are also in good agreement and vary between 0.3 and 1.2 Tg, while the MODIS ash corrected 8.7 μm SO2 masses vary between 0.4 and 2.7 Tg. The mass increase with time confirms the continuous SO2 injection in the atmosphere after the main explosive episodes. Moreover the difference between the 7.3 and 8.7 μm retrievals suggests a vertical stratification of the volcanic cloud. The results also confirm the importance of the ash correction; the corrected 8.7 μm SO2 total masses are less than 30–40% of the uncorrected values.

Tracking and quantifying volcanic SO<sub>2</sub> with IASI, the September 2007 eruption at Jebel at Tair

Abstract. In this paper we demonstrate the potential of the infrared Fourier transform spectrometer IASI in analysing volcanic eruptions, using the September 2007 eruption at Jebel at Tair as an illustrative example. Detailed radiative transfer calculations are presented, simulating IASI-like transmittance spectra for a variety of volcanic plumes. We analyse the sensitivity of IASI to SO2 at different altitudes and demonstrate that IASI is in principle capable of sensing SO2 down to the surface. Using the brightness temperature difference of well chosen SO2 channels as a filter, we are able to track the plume of the Jebel at Tair eruption for 12 days, on a par with state of the art UV sounders. A method is presented for quickly estimating the altitude of a volcanic plume based on the relative intensities of the SO2 absorption lines. Despite recent advances, it is still very challenging to retrieve vertical profiles of SO2 from nadir viewing satellites. Currently the most accurate profiles in nadir are retrieved using backtracking of the plume with atmospheric transport models. Via full inverse retrievals using the optimal estimation method, we show the possibility of extracting medium coarse vertical profiles from IASI data. The retrieval allows us to present an evolution of the total mass of SO2 in the plume for the Jebel at Tair eruption. An analytical relation is derived between brightness temperature differences and concentrations, which fits the experimental data very well. The spectral range of IASI also allows retrieval of volcanic aerosols. In the initial plume of the Jebel at Tair eruption, volcanic aerosols were found in the form of ice particles, for which we derived particle sizes.

Slagging Characteristics during Residential Combustion of Biomass Pellets

Limited availability of sawdust and planer shavings and an increasing demand for biomass pellets in Europe are pushing the market toward other, more problematic raw materials with broader variation in total fuel ash content and composition of the ash forming elements as well as in their slagging tendencies. The main objective in the present work was therefore to determine the influence of fuel−ash composition on residual ash and slag behavior. Twelve different biomass pellets were used: reed canary grass (two different samples), hemp (two different samples), wheat straw, salix, logging residues (two different samples), stem wood (sawdust) as well as spruce, pine, and birch bark. The different pellet qualities were combusted in a commercial under fed pellet burner (20 kW) installed in a reference boiler. Continuous measurements of O2, CO, CO2, HCl, SO2, and total particle matter mass concentrations were determined in the exhaust gas directly after the boiler. The collected slag deposits, the corresponding ...

Physical and Chemical Characterization of Residential Oil Boiler Emissions

The toxicity of emissions from the combustion of home heating oil coupled with the regional proximity and seasonal use of residential oil boilers (ROB) is an important public health concern. Yet scant physical and chemical information about the emissions from this source is available for climate and air quality modeling and for improving our understanding of aerosol-related human health effects. The gas- and particle-phase emissions from an active ROB firing distillate fuel oil (commonly known as diesel fuel) were evaluated to address this deficiency. Ion chromatography of impactor samples showed that the ultrafine ROB aerosol emissions were approximately 45% (w/w) sulfate. Gas chromatography-mass spectrometry detected various n-alkanes at trace levels, sometimes in accumulation mode particles, and out of phase with the size distributions of aerosol mass and sulfate. The carbonaceous matter in the ROB aerosol was primarily light-adsorbing elemental carbon. Gas chromatography-atomic emission spectroscopy measured a previously unrecognized organosulfur compound group in the ROB aerosol emissions. High-resolution transmission electron microscopy of ROB soot indicated the presence of a highly ordered primary particle nanostructure embedded in larger aggregates. Organic gas emissions were measured using EPA Methods TO-15 and TO-11A. The ROB emitted volatile oxygenates (8 mg/(kg of oil burned)) and olefins (5 mg/(kg of oil burned)) mostly unrelated to the base fuel composition. In the final analysis, the ROB tested was a source of numerous hazardous air pollutants as defined in the Clean Air Act Amendments. Approximations conducted using emissions data from the ROB tests show relatively low contributions to a regional-level anthropogenic emissions inventory for volitile organic compounds, PM2.5, and SO2 mass.

Simultaneous retrieval of volcanic ash and SO2 using MSG‐SEVIRI measurements

Volcanic ash and sulphur dioxide masses from the November 2005 eruption of Karthala volcano, Comoros Islands, are simultaneously retrieved using rapid‐scan, multispectral infrared measurements from the Spin Enhanced Visible and Infrared Imager on board the Meteosat Second Generation geosynchronous satellite. Retrievals are made every 15 min, which show that the ash and SO2 separate in the vertically sheared atmosphere producing a fast moving upper level (∼12 km) SO2 cloud, a slower moving middle level (∼8 km) ash cloud and a boundary layer (<3 km) SO2 plume. The total mass of fine ash is 0.1 ± 0.05 Tg (SiO2), the upper level SO2 mass is 0.19 ± 0.01 Tg (S) while the boundary layer SO2 mass is 0.009 ± 0.01 Tg (S). These are the first simultaneous satellite measurements of ash and SO2 from an erupting volcano and confirm previous ideas about vertical separation. We suggest care must be exercised when using SO2 as a tracer for volcanic ash in aviation hazard warning systems.

Simultaneous Removal of NO and SO2 by High-Temperature Fluidized Zero-Valent Iron Processes

A new approach to simultaneously remove nitrogen mon-oxide (NO) and sulfur dioxide (SO2) by zero valent iron (ZVI) was investigated. Three different parameters, temperature, flux, and ZVI dosage, were tested in fluidized ZVI column studies containing 500 ppmv of NO and SO2, respectively. Under the ZVI dosage of 0.5 g at flux of 0.6 L/cm2·min for temperature 573 K, there is neither NO nor SO2 reduction. For 623 K and 673 K, complete removal for NO and >90% removal for SO2 were achieved. For temperatures of 723 K and 773 K, 100% removal was achieved for both NO and SO2. The amounts of NO or SO2 reduction (as milligrams of NO or SO2 per gram ZVI) increased as temperature increased, and linearities were observed with both correlation coefficients >0.97. Compared with NO, SO2 had earlier breakthrough because of a slower diffusion rate and less reactivity but higher mass reduction because of a higher molecular weight for SO2 (64 g/mol for SO2 and 30 g/mol for NO). At same temperature, both NO and SO2 reductions (as milligrams of NO or SO2 per gram of ZVI) were constant regardless of either flux or ZVI dosage variation, but breakthrough time was affected by both flux and ZVI dosage. A parameter weight of ZVI/flux (W/F) was developed to represent these two parameters at the same time to assess the breakthrough time of NO and SO2. Higher breakthrough time was achieved for higher W/F value. Moreover, interestingly, longer breakthrough time and more NO and SO2 mass reduction were achieved for combined NO and SO2 than individual NO or SO2 treated by ZVI, and both oxidation and reduction reactions occurred instead of a reduction reaction only. Chemical reactions among ZVI/NO, ZVI/ SO2, and ZVI/NO/SO2 were also proposed and verified by X-ray diffraction analyses.

The Influence of Chemical Reaction on Mass Transfer Behavior in the Membrane Absorption Process

Special reaction systems were proposed to investigate the mechanism of the mass transfer process in the membrane absorption process. The mass transfer resistance of this process was calculated by using hydrophobic polypropylene (PP) hollow fiber membrane (HFM); and a 2‐order partial differential model, including reaction, was developed to describe the SO2 and CO2 absorption process using HFM. Throughout the experimental analyzing and model results, for either SO2/air/NaOH system or CO2/air‐NaOH system, different phenomena in these two systems were discussed. Since the reaction mechanisms of both the SO2‐NaOH system and the CO2‐NaOH system were different, the SO2 and CO2 mass transfer in liquid side were different. The relation between the chemical reaction mechanism and mass transfer, instead of the ionized effect, was the reason for deviation in SO2 absorption process. The influence of liquid phase velocity and the concentration of absorbent on the mass transfer process was also discussed.

A Passive Method of Nondispersion Correlation Spectroscopy for Remote Monitoring of the Content of CO, SO2, and NO2 in the Atmosphere

The possibility of using a passive method of nondispersion correlation spectroscopy for remote monitoring of the content of the priority gaseous pollutants in the atmosphere with the aid of direct IR and UV solar radiation is considered. The calibration characteristics and noise immunity of nondispersion correlation radiometers used in determining the absorption mass of CO, SO2, and NO2 have been investigated.

Re‐evaluation of SO2 release of the 15 June 1991 Pinatubo eruption using ultraviolet and infrared satellite sensors

In this study, ultraviolet TOMS (Total Ozone Mapping Spectrometer) satellite data for SO2 are re‐evaluated for the first 15 days following the 15 June 1991 Pinatubo eruption to reflect new data retrieval and reduction methods. Infrared satellite SO2 data from the TOVS/HIRS/2 (TIROS (Television Infrared Observation Satellite) Optical Vertical Sounder/High Resolution Infrared Radiation Sounder/2) sensor, whose data sets have a higher temporal resolution, are also analyzed for the first time for Pinatubo. Extrapolation of SO2 masses calculated from TOMS and TOVS satellite measurements 19–118 hours after the eruption suggest initial SO2 releases of 15 ± 3 Mt for TOMS and 19 ± 4 Mt for TOVS, including SO2 sequestered by ice in the early Pinatubo cloud. TOVS estimates are higher in part because of the effects of early formed sulfate. The TOMS SO2 method is not sensitive to sulfate, but can be corrected for the existence of this additional emitted sulfur. The mass of early formed sulfate in the Pinatubo cloud can be estimated with infrared remote sensing at about 4 Mt, equivalent to 3 Mt SO2. Thus the total S release by Pinatubo, calculated as SO2, is 18 ± 4 Mt based on TOMS and 19 ± 4 Mt based on TOVS. The SO2 removal from the volcanic cloud during 19–374 hours of atmospheric residence describes overall e‐folding times of 25 ± 5 days for TOMS and 23 ± 5 days for TOVS. These removal rates are faster in the first 118 hours after eruption when ice and ash catalyze the reaction, and then slow after heavy ash and ice fallout. SO2 mass increases in the volcanic cloud are observed by both TOMS and TOVS during the first 70 hours after eruption, most probably caused by the gas‐phase SO2 release from sublimating stratospheric ice‐ash‐gas mixtures. This result suggests that ice‐sequestered SO2 exists in all tropical volcanic clouds, and at least partially explains SO2 mass increases observed in other volcanic clouds in the first day or two after eruption.

Correlations between eruption magnitude, SO 2 yield, and surface cooling

Abstract Sulphurous gases from explosive eruptions have the potential to form stratospheric aerosols and so produce surface cooling on a hemispheric to global scale. However, testing for any correlation between SO 2 yield and surface cooling is hampered by instrumental SO 2 and temperature measurements being available for time periods that include only a few large eruptions. To overcome this, published dendroclimatological data, satellite (Total Ozone Mapping Spectrometer) data on SO 2 emissions, stratospheric optical depth data, and volcanological observations are integrated, revealing several relevant new correlations. First, the efficient conversion of SO 2 into stratospheric aerosols occurs when the ratio of plume height to tropopause height is greater than about 1.5. Second, the mass of emitted SO 2 correlates well with the mass of erupted magma. The SO 2 yield is 0.1 to 1% by mass of magma, irrespective of composition. The best-fit power law ( r 2 =0.67) is mass of SO 2 in Mt=1.77(mass of magma in Gt) 0.64 . Third, of the eruption clouds that are believed to have entered the stratosphere in the period 1400–1994, those with masses <5 Gt magma (DRE <2 km 3 ) appear to have had insignificant effects on Northern Hemisphere summer temperature. The scattered data for eruptions of >10 Gt (>4 km 3 ) magma suggest a mean cooling effect of about 0.35 °C.

Morphological and structural change of nano-pored alumina membrane above 1200 K

The transition and the change in pore morphology of a porous alumina membrane prepared by anodically oxidizing aluminum in sulfuric acid were studied mainly by TG-DTA, TMA, dilatometry and TEM. At ca. 1243 K, TMA showed an expansion followed by contraction; the CO2 and SO2 gases were quickly discharged, and the pore morphology of the as-prepared porous membrane (ca 150 m-t, with pores ca 25 nm in diameter and containing ca 11% by mass of SO2) showed an abrupt change, but the pores were retained to ca. 1573 K. Sulfur incorporated in the membrane was lost in two stages, i.e., at ca 1243 K and in a range up to 1373 K. Isothermal measurements revealed the complex crystallization of the amorphous phase into polycrystalline phase.

HCl emissions at Soufrière Hills Volcano, Montserrat, West Indies, during a second phase of dome building: November 1999 to October 2000

HCl:SO2 mass ratios measured by open path Fourier transform spectroscopy (OP-FTIR) in the volcanic plume at Soufriere Hills Volcano, Montserrat, are presented for the second phase of dome building between November 1999 and November 2000. HCl:SO2 mass ratios of greater than 1 and HCl emission rates of greater than 400 t day–1 characterise periods of dome building for this volcano. The data suggest that chlorine partitions into a fluid phase as the magma decompresses and exsolves water during ascent. This is substantiated by a correlation between chlorine and water content in the melt (derived from the geochemical analysis of plagioclase melt inclusion and matrix glasses from phase I and II of dome growth). The matrix glass from the November 1999 and March 2000 domes indicate an open system degassing regime with a fluid-melt partition coefficient for chlorine of the order of 250–300. September 1997 glasses have higher chlorine contents and may indicate a switch to closed system degassing prior to explosive activity in September and October 1997. The OP-FTIR HCl time series suggests that HCl emission rate is strongly related to changes in eruption rate and we infer an emission rate of over 13.5 kt day–1 HCl during a period of high extrusion rate in September 2000. A calculation of the HCl emission rate expected for varying extrusion rates from the open-system degassing model suggests a HCl emission rate of the order of 1–4 kt day–1 is indicative of an extrusion rate of between 2 and 8 m3 s–1. Monitoring of HCl at Soufriere Hills Volcano provide a proxy for extrusion rate, with changes in ratio between HCl and SO2 occurring rapidly in the plume. Order of magnitude changes occur in HCl emission rates over the time-scale of hours to days, making these changes easy to detect during the day-to-day monitoring of the volcano. Mean water emission rates are calculated to range from 9–24 kt day–1 during dome building activity, calculated from the predicted mass ratio of H2O:HCl in the fluid at the surface and FTIR-derived HCl emission rates.

New estimates of sulfur degassing and atmospheric mass-loading by the 934 AD Eldgjá eruption, Iceland

The 934 AD Eldgjá basaltic flood lava eruption in southern Iceland is the largest on Earth in the last millennium. The Eldgjá fissures produced 19.6km3 of transitional basalt in a prolonged eruption that featured at least eight distinct episodes and may have lasted for 3–8 years. The atmospheric SO2 mass loading by Eldgjá is determined by new measurements of pre-eruption and residual sulfur contents in the products from all phases of the eruption. A pre-eruption sulfur content of ∼2150ppm indicates that the magma carried 232Mt of SO2 to the surface, where vent and lava flow degassing released 219Mt into the atmosphere. This value corresponds to a potential H2SO4-aerosol yield of ∼450Mt, increasing previous H2SO4-aerosol mass estimates by a factor of 2.6–4.5. Approximately 79% of the original sulfur mass was released at the vents, indicating ∼185Mt SO2 were discharged into the atmosphere above the Eldgjá fissures and carried aloft by the eruption columns to upper tropospheric and lower stratospheric altitudes (∼15km). Consequently, only ∼35Mt SO2 escaped from the lava into the lower troposphere. These estimates of the SO2 mass loading from Eldgjá make it the greatest known volcanic pollutant of recent history, exceeding that of 1783 AD Laki and 1815 AD Tambora eruptions by factors of 1.8 and 2.0–2.8, respectively. However, the intensity of climatic effects deduced by the Eldgjá event are not thought to have surpassed that of Laki or Tambora because the eruption was prolonged and subsequently the sulfur emissions were drawn out over several years. The lack of detailed historic records for this period make estimates of the effects of long term but significant release of SO2 (30–70Mt/yr) on the atmosphere uncertain.