Current challenges in modelling far-range air pollution induced by the 2014–2015 Bárðarbunga fissure eruption (Iceland)

Abstract

Abstract. The 2014–2015 Holuhraun lava-flood eruption of Bárðarbunga volcano (Iceland) emitted prodigious amounts of sulfur dioxide into the atmosphere. This eruption caused a large-scale episode of air pollution throughout Western Europe in September 2014, the first event of this magnitude recorded in the modern era. We gathered chemistry-transport simulations and a wealth of complementary observations from satellite sensors (OMI, IASI), ground-based remote sensing (lidar, sunphotometry, differential optical absorption spectroscopy) and ground-level air quality monitoring networks to characterize both the spatial-temporal distributions of volcanic SO2 and sulfate aerosols as well as the dynamics of the planetary boundary layer. Time variations of dynamical and microphysical properties of sulfate aerosols in the aged low-tropospheric volcanic cloud, including loading, vertical distribution, size distribution and single scattering albedo, are provided. Retrospective chemistry-transport simulations at low horizontal resolution (25 km × 25 km) capture the correct temporal dynamics of this far-range air pollution event but fail to reproduce the correct magnitude of SO2 concentration at ground-level. Simulations at higher spatial resolution, relying on two nested domains with finest resolution of 7.3 km × 7.3 km, improve substantially the far-range vertical distribution of the volcanic cloud and subsequently the description of ground-level SO2 concentrations. However, remaining discrepancies between model and observations are shown to result from an inaccurate representation of the planetary boundary layer (PBL) dynamics. Comparison with lidar observations points out a systematic under-estimation of the PBL height by the model, whichever the PBL parameterization scheme. Such a shortcoming impedes the capture of the overlying Bárðarbunga cloud into the PBL at the right time and in sufficient quantities. This study therefore demonstrates the key role played by the PBL dynamics in accurately modelling large-scale volcanogenic air pollution.

The operational eEMEP model version 10.4 for volcanic SO<sub>2</sub> and ash forecasting

“…A simplified emissions term is used where SO 2 is released at a constant rate, uniformly distributed over three emissions heights, to see which height produces a simulation that matches better with observations. With some discrepancies caused by the description of the planetary boundary layer also found in Schmidt et al (2015) with the Lagrangian NAME model and in Boichu et al (2016) with the Eulerian CHIMERE model, the EMEP MSC-W model matches well the observed surface SO 2 timing and concentration levels. Compared to SO 2 column satellite observations from the Ozone Monitoring Instrument (OMI), similar mass loadings and dispersion patterns are found.…”

Satellite-derived sulfur dioxide (SO<sub>2</sub>) emissions from the 2014–2015 Holuhraun eruption (Iceland)

“…Sulfur dioxide (SO 2 ) is one of the most important magmatic volatiles for volcanic geochemical analysis and hazard assessments due to its low ambient concentrations, abundance in volcanic plumes and spectroscopic features. Tropospheric volcanic SO 2 and its conversion products can affect the environment, human health, air quality and the radiative balance of the Earth (Schmidt et al, 2015;Gíslason et al, 2015;Schmidt et al, 2012;Gettelman et al, 2015;Ilyinskaya et al, 2017;Boichu et al, 2016;McCoy and Hartmann, 2015;Malavelle et al, 2017). Measurements of SO 2 from volcanic eruptions are vital, both to understanding the under-E. Carboni et al: 2014Carboni et al: -2015 Holuhraun eruption lying volcanic processes and also the wider-scale environmental impacts of volcanism.…”

“…The Infrared Atmospheric Sounding Interferometers (IASI) on board the Metop satellite platforms provide several observations of Holuhraun each day. The plume altitude and the SO 2 column amount are retrieved from the measured top-of-atmosphere spectral radiance (Carboni et al, 2012). For the first month of the Holuhraun eruption, previous studies have shown good agreement between IASI measurements and those from the Ozone Monitoring Instrument (OMI), ground-based and balloon-borne measurements and atmospheric dispersion model simulations (Schmidt et al, 2015;Vignelles et al, 2016).…”

Satellite-derived sulphur dioxide (SO<sub>2</sub>) emissions from the 2014–2015 Holuhraun eruption (Iceland)

“…The details of the retrieval scheme are summarised briefly below. For more details see Carboni et al (2012Carboni et al ( , 2016). An SO 2 retrieval is performed for all IASI pixels that present a positive result in the SO 2 detection scheme (Walker et al, 2011.…”

“…Sulfur dioxide (SO 2 ) is one of the most important magmatic volatiles for volcanic geochemical analysis and hazard assessments due to its low ambient concentrations, abundance in volcanic plumes and spectroscopic features. Tropospheric volcanic SO 2 and its conversion products can affect the environment, human health, air quality and the radiative balance of the Earth (Schmidt et al, 2015;Gíslason et al, 2015;Schmidt et al, 2012;Gettelman et al, 2015;Ilyinskaya et al, 2017;Boichu et al, 2016;McCoy and Hartmann, 2015;Malavelle et al, 2017). Measurements of SO 2 from volcanic eruptions are vital, both to understanding the under-lying volcanic processes and also the wider-scale environmental impacts of volcanism.…”