Rapid primary sulphate aerosol generation observed with OP FTIR in the eruptive plume of the Fagradalsfjall basaltic eruption, Iceland, 2021
Open-Path Fourier-Transform Infrared (OP-FTIR) absorption spectroscopy is a powerful method for remote characterisation 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 volat...
| Published in: | Journal of Geophysical Research: Atmospheres |
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| Main Authors: | , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
American Geophysical Union
2024
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| Subjects: | |
| Online Access: | https://doi.org/10.1029/2023JD040574 https://ora.ox.ac.uk/objects/uuid:e646e073-977a-4ee1-b434-7c2a71e0966f |
| Summary: | Open-Path Fourier-Transform Infrared (OP-FTIR) absorption spectroscopy is a powerful method for remote characterisation 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 characterise the emission-absorption behaviour 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. Temperaturedependent SO2/SO4 2- 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 sulphur partitioning and volcanic plume evolution, with the potential to improve volcano monitoring and quantification of air quality hazard assessments. |
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