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Rapid Primary Sulfate Aerosol Generation Observed With OP‐FTIR in the Eruptive Plume of the Fagradalsfjall Basaltic Eruption, Iceland, 2021.

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Title: Rapid Primary Sulfate Aerosol Generation Observed With OP‐FTIR in the Eruptive Plume of the Fagradalsfjall Basaltic Eruption, Iceland, 2021.
Authors: Smekens, Jean‐François1,2 (AUTHOR) Jean-Francois.Smekens@nau.edu, Mather, Tamsin A.1 (AUTHOR), Burton, Mike R.3,4 (AUTHOR), Varnam, Matthew3,5 (AUTHOR), Pfeffer, Melissa A.6 (AUTHOR)
Source: Journal of Geophysical Research. Atmospheres. 6/28/2024, Vol. 129 Issue 12, p1-20. 20p.
Subject Terms: *Volcanic eruptions, *Air quality monitoring, *Particulate matter, *Volcanic gases, Sulfate aerosols, Volcanic plumes
Geographic Terms: Iceland
Abstract: Open‐Path Fourier‐Transform Infrared (OP‐FTIR) absorption spectroscopy is a powerful method for remote characterization of volcanic plume composition from safe distances. Many studies have used it to examine the composition of volcanic gas emitted at the surface, which is influenced by initial volatile contents and magma ascent/storage processes, and help to reveal the dynamics controlling surface activity. However, to evaluate the health hazard threats associated with volcanic emissions and their potential impact on wider atmospheric conditions, near‐source particle measurements are also key. Here we present a forward model and fitting algorithm which allows quantification of particle size and abundance. This was successfully applied to radiometrically uncalibrated OP‐FTIR spectra collected with a highly dynamic radiation source during the Fagradalsfjall eruption, Iceland, on 11 August 2021. Quantification of plume temperatures ranging from 350 to 650 K was essential to characterize the emission‐absorption behavior of SO2, enabling retrievals of particulate matter in the thermal infrared spectral window (750–1250 cm−1) in each spectrum. For the first time, we observe the rapid formation of primary aerosols in young plumes (only a few seconds old) with OP‐FTIR. Temperature‐dependent SO2/SO42− molar ratios range from 100 to 250, consistent with a primary formation mechanism controlled by cooling and entrainment of atmospheric gases. This novel aerosol spectrum retrieval opens new frontiers in field‐based measurements of sulfur partitioning and volcanic plume evolution, with the potential to improve volcano monitoring and quantification of air quality hazard assessments. Plain Language Summary: Open‐Path Fourier‐Transform Infrared (OP‐FTIR) spectroscopy is often used during volcanic eruptions to identify and quantify the amounts of different gases released during eruptions from a safe distance. This is important because gas compositions contain information about where magma came from and how it rose to the surface and erupted, and help us understand the impact of eruptions on air quality and climate. This paper presents a new way of analyzing spectra which allows us to quantify the amount and composition of aerosols, small droplets of water and other chemicals such as sulfuric acid. These aerosols can have important impacts on air quality and local climate, or even global climate in the case of large eruptions. We used this new approach during an eruption in 2021 on Iceland, pointing the instrument directly at the erupting vent, and were able to observe the formation of aerosols very close to their emission point, where they undergo rapid cooling. This is the first time we have been able to directly measure this aerosol formation process during an eruption. Our work opens new opportunities to re‐analyze older data to extract further insights and provides new opportunities to better understand the impacts of future eruptions. Key Points: We present a new method for retrieving water and sulfate aerosol column densities from Open‐Path Fourier‐Transform Infrared measurements of near‐source volcanic plumesTemperature‐dependent SO2/SO42− ratios range from 100 in colder plumes to 250 in hotter plumesThis method enables quantitative observation of primary aerosol formation in young plumes, a few seconds after emission [ABSTRACT FROM AUTHOR]
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Abstract:Open‐Path Fourier‐Transform Infrared (OP‐FTIR) absorption spectroscopy is a powerful method for remote characterization of volcanic plume composition from safe distances. Many studies have used it to examine the composition of volcanic gas emitted at the surface, which is influenced by initial volatile contents and magma ascent/storage processes, and help to reveal the dynamics controlling surface activity. However, to evaluate the health hazard threats associated with volcanic emissions and their potential impact on wider atmospheric conditions, near‐source particle measurements are also key. Here we present a forward model and fitting algorithm which allows quantification of particle size and abundance. This was successfully applied to radiometrically uncalibrated OP‐FTIR spectra collected with a highly dynamic radiation source during the Fagradalsfjall eruption, Iceland, on 11 August 2021. Quantification of plume temperatures ranging from 350 to 650 K was essential to characterize the emission‐absorption behavior of SO2, enabling retrievals of particulate matter in the thermal infrared spectral window (750–1250 cm−1) in each spectrum. For the first time, we observe the rapid formation of primary aerosols in young plumes (only a few seconds old) with OP‐FTIR. Temperature‐dependent SO2/SO42− molar ratios range from 100 to 250, consistent with a primary formation mechanism controlled by cooling and entrainment of atmospheric gases. This novel aerosol spectrum retrieval opens new frontiers in field‐based measurements of sulfur partitioning and volcanic plume evolution, with the potential to improve volcano monitoring and quantification of air quality hazard assessments. Plain Language Summary: Open‐Path Fourier‐Transform Infrared (OP‐FTIR) spectroscopy is often used during volcanic eruptions to identify and quantify the amounts of different gases released during eruptions from a safe distance. This is important because gas compositions contain information about where magma came from and how it rose to the surface and erupted, and help us understand the impact of eruptions on air quality and climate. This paper presents a new way of analyzing spectra which allows us to quantify the amount and composition of aerosols, small droplets of water and other chemicals such as sulfuric acid. These aerosols can have important impacts on air quality and local climate, or even global climate in the case of large eruptions. We used this new approach during an eruption in 2021 on Iceland, pointing the instrument directly at the erupting vent, and were able to observe the formation of aerosols very close to their emission point, where they undergo rapid cooling. This is the first time we have been able to directly measure this aerosol formation process during an eruption. Our work opens new opportunities to re‐analyze older data to extract further insights and provides new opportunities to better understand the impacts of future eruptions. Key Points: We present a new method for retrieving water and sulfate aerosol column densities from Open‐Path Fourier‐Transform Infrared measurements of near‐source volcanic plumesTemperature‐dependent SO2/SO42− ratios range from 100 in colder plumes to 250 in hotter plumesThis method enables quantitative observation of primary aerosol formation in young plumes, a few seconds after emission [ABSTRACT FROM AUTHOR]
ISSN:2169897X
DOI:10.1029/2023JD040574