Large-scale particulate air pollution and chemical fingerprint of volcanic sulfate aerosols from the 2014-15 Holuhraun flood lava eruption of Bárðarbunga volcano (Iceland).

Volcanic sulfate aerosols play a key role on air quality and climate. However, the oxidation of sulfur dioxide (SO₂) precursor gas to sulfate aerosols (SO₄²⁻) in volcanic clouds is poorly known, especially in the troposphere. Here we determine the chemical speciation, lifetime and impact on air quality of sulfate aerosols from the 2014–15 Holuhraun flood lava eruption of Bárðarbunga icelandic volcano. To do so, we jointly analyze a set of SO₂ observations from satellite (OMPS and IASI) and ground-level measurements from air quality monitoring stations together with, for the first time, high temporal resolution mass spectrometry measurements of Aerosol Chemical Speciation Monitor (ACSM) performed far from the source. We explore month/year-long ACSM data in France from stations in contrasted environments, close and far from industrial sulfur-rich activities. We demonstrate that aged volcanic sulfate aerosols exhibit a distinct chemical fingerprint, with NO₃ : SO₄ and Organic : SO₄ concentration ratios higher than freshly-emitted industrial sulfate but lower than background aerosols in urban/rural conditions. Combining AERONET (AErosol RObotic NETwork) sunphotometric data with ACSM observations, we also show a long persistence over weeks of volcanic sulfate aerosols while SO₂ disappears in a few days at most. Finally, gathering 6 month-long datasets from 19 sulfur monitoring stations of the EMEP (European Monitoring and Evaluation Programme) network allows us to demonstrate a much broader large-scale European particulate pollution in SO₄ associated to the Holuhraun eruption, from Scandinavia to France. Exploiting these in-situ data, we also show the various rates of SO₂ oxidation observed in the volcanic cloud, with SO₂ : SO₄ concentration ratios ranging in 0.6–7, distinct from background conditions of about 50. Most current studies generally focus on SO₂, an unambiguous and more readily measured marker of the volcanic cloud. However, our results here on sulfate aerosols raise fundamental questions about the cumulative impact of tropospheric eruptions on air quality, health, atmospheric composition and climate, which may be significantly underestimated. [ABSTRACT FROM AUTHOR]