SO2 emission rates and incorporation into the air pollution dispersion forecast during the 2021 eruption of Fagradalsfjall, Iceland
Artikel i vetenskaplig tidskrift, 2024

During the low-effusion rate Fagradalsfjall eruption (19 March – 18 September 2021), the emission of sulfur dioxide (SO2) was frequently measured using ground-based UV spectrometers. The total SO2 emitted during the entire eruption was 970 ± 540 kt, which is only about 6% of the SO2 emitted during the similar length Holuhraun eruption (2014–2015). The eruption was divided into five phases based on visual observations, including the number of active vents and the occurrence of lava fountaining. The SO2 emission rate ranged from 44 ± 19 kg/s in Phase 2 to 85 ± 29 kg/s in Phase 5, with an average of 64 ± 34 kg/s for the entire eruption. There was notable variability in SO2 on short timescales, with measurements on 11 August 2021 ranging from 17 to 78 kg/s. SO2 flux measurements were made using scanning DOAS instruments located at different distances from and orientations relative to the eruption site augmented by traverses. Four hundred and forty-four scan and traverse measurements met quality criteria and were used, along with plume height and meteorological data, to calculate SO2 fluxes while accounting for wind-related uncertainties. A tendency for stronger SO2 flux concurrent with higher amplitude seismic tremor and the occurrence of lava fountaining was observed during Phases 4 and 5 which were characterized by intermittent crater activity including observable effusion of lava and gas release interspersed with long repose times. This tendency was used to refine the calculation of the amount of SO2 emitted during variably vigorous activity. The continuous seismic tremor time series was used to quantify how long during these eruption phases strong/weak activity was exhibited to improve the calculated SO2 flux during these Phases. The total SO2 emissions derived from field measurements align closely with results obtained by combining melt inclusion and groundmass glass analyses with lava effusion rate measurements (910 ± 230 kt SO2). Specifically, utilizing the maximum S content found in evolved melt inclusions and the least remaining S content in accompanying quenched groundmasses provides an identical result between field measurements and the petrological calculations. This suggests that the maximum SO2 release calculated from petrological estimates should be preferentially used to initialize gas dispersion models for basaltic eruptions when other measurements are lacking. During the eruption, the CALPUFF dispersion model was used to forecast ground-level exposure to SO2. The SO2 emission rates measured by DOAS were used as input for the dispersion model, with updates made when a significant change was measured. A detailed analysis of one mid-distance station over the entire eruption shows that the model performed very well at predicting the presence of volcanic SO2 when it was measured. However, it frequently predicted the presence of SO2 that was not measured and the concentrations forecasted had no correlation with the concentrations measured. Various approaches to improve the model forecast were tested, including updating plume height and SO2 flux source terms based on measurements. These approaches did not unambiguously improve the model performance but suggest that improvements might be achieved in more-polluted conditions.

SO 2


Volcanic pollution




M. A. Pfeffer

Icelandic Meteorological Office

Santiago Arellano

Chalmers, Rymd-, geo- och miljövetenskap, Geovetenskap och fjärranalys

S. Barsotti

Icelandic Meteorological Office

Guðrún Nína Petersen

Icelandic Meteorological Office

Talfan Barnie

Icelandic Meteorological Office

Evgenia Ilyinskaya

University of Leeds

Tryggvi Hjörvar

Icelandic Meteorological Office

European Centre for Medium-Range Weather Forecasts

E. Bali

Nordic Volcanological Center

G. B.M. Pedersen

Nordic Volcanological Center

Gunnar B. Guðmundsson

Icelandic Meteorological Office

Kristín Vogfjorð

Icelandic Meteorological Office

Eemu Johannes Ranta

Nordic Volcanological Center

Helsingin Yliopisto

Bergrún Arna Óladóttir

Icelandic Meteorological Office

Nordic Volcanological Center

Brock A. Edwards

University of Manitoba

Commission Geologique du Canada

Yves Moussallam

Lamont-Doherty Earth Observatory

Andri Stefánsson

Nordic Volcanological Center

Samuel Warren Scott

Nordic Volcanological Center

Jean Francois Smekens

Northern Arizona University

University of Oxford

Matthew Varnam

University of Arizona

University of Manchester

Manuel Titos

Universidad de Granada

Journal of Volcanology and Geothermal Research

0377-0273 (ISSN)

Vol. 449 108064


Hållbar utveckling


Multidisciplinär geovetenskap



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