Major impact of volcanic gases on the chemical composition of precipitation in Iceland during the 2014–2015 Holuhraun eruption

Abstract

The Holuhraun eruption in 2014–2015 was the largest in Iceland for more than 200 years. It resulted in emissions of large quantities of volcanic gases into the atmosphere (11 megaton (Mt) SO2, 0.1 Mt HCl, and 0.05 Mt HF). During the eruption the volcanic gases had major effects on F, SO4 and to a lesser extent Cl concentrations in precipitaxtion throughout Iceland, effects not observed in recent decades. The concentrations of F, Cl, and SO4 (n = 705) reached values of 444 µm 12,270 µm, and 17,324 µm during the eruption and were on average ~20 times higher for F and SO4 and much lower for Cl compared to preeruption times. The concentrations of major cations (Si, Na, K, Ca, Mg, Al, and Fe) (n = 151) in the precipitation were taken as having originated from seawater spray and dissolution of rock dust and aerosol. Based on the mixing model developed here, it is demonstrated that the source of the enrichment of F and SO4 was indeed the volcanic gas emissions with >60–100 mol % of SO4 and F in the precipitation originated from volcanic gas, whereas the Cl originated mostly from seawater spray, making the volcanic gas input of Cl relatively less important than for F and SO4. The results showed that large volcanic eruptions can have major effects on atmospheric chemistry and impact the composition of precipitation.

Pollution from the 2014–15 Bárðarbunga eruption monitored by snow cores from the Vatnajökull glacier, Iceland

“…The 2014-2015 Bárðarbunga eruption (Sigmundsson et al, 2015, Galeczka et al 2016Gudmundsson et al, 2016;Gauthier et al 2016, Stefánsson et al 2017a) brought the possible effects of sustained eruptive degassing in the troposphere to the world's attention. Eruption vents during the 2014-15 Bárðarbunga eruption were located on the outwash plains of the Dyngjujökull glacier, on the historical Holuhraun lava that erupted between 1794 and 1864 ( Fig.…”

“…Similar SO2 fluxes were reported by Gauthier and co-workers (2016) and equalled 97 kt/day). These high emissions affected rain and snow chemical composition all over Iceland (Gislason et al, 2015;Stefánsson et al, 2017a).. During winter and/or in cold areas, gasses and aerosols sourced by natural and manmade activities are transported and may accumulate in snow. Globally, aerosols are sourced from oceans (1000 Mt/yr), soils or continental surface (so called continental aerosols; 100-1000 Mt/yr), and anthropogenic and volcanic activities (Shaw, 1989).…”

Photochemical box modelling of volcanic SO<sub>2</sub> oxidation: isotopic constraints

“…Climatic perturbations from volcanic emissions are principally caused by conversion of sulfur gases into sulfate aerosols, which can then interact with solar and terrestrial radiation via scattering and absorption (Stocker et al, 2013). Once injected into the troposphere, volcanic SO 2 is converted in few days typically to H 2 SO 4 by a range of gas-phase and liquid-phase reactions taking place in volcanic plumes and clouds (Chin and Jacob, 1996;Stevenson et al, 2003a). In the atmosphere, depending on the oxidation pathway, H 2 SO 4 is produced either in the gas phase or liquid phase.…”

“…Volcanic quiescent degassing and eruptions is an important natural source of SO 2 , notably to the free troposphere (Bates et al, 1992;Graf et al, 1998). Volcanic emissions release about 10-13 Tg y −1 of SO 2 to the atmosphere (Andres and Kasgnoc, 1998) and contribute to up to 10 % of total sulfur emissions to the atmosphere (Stevenson et al, 2003a). Remarkably, volcanic emissions also have a bigger impact on the tropospheric aerosol burden than other sulfur sources (Graf et al, 1998) because volcanoes tend to emit SO 2 at higher altitudes than most other surface sulfur emissions, where the lifetime is longer.…”

“…Most of the tropospheric sulfate is generated in the liquid phase (Alexander et al, 2009) via oxidation of aqueous SO 2 by dissolved oxidants of the atmosphere, such as H 2 O 2 , O 3 , O 2 catalysed by transition metal ions (Fe(III) and Mn(II)) and, possibly, HOBr and HOCl (Vogt et al, 1996;von Glasow et al, 2002;Stevenson et al, 2003a;Berglen et al, 2004;Park et al, 2004;Alexander et al, 2009;von Glasow and Crutzen, 2013;Chen et al, 2016). Note that the importance of the halogen oxidation pathway remains unclear.…”