Abstract
Abstract. We developed an optimal-estimation algorithm to simultaneously retrieve, for the first time, coexisting volcanic gaseous SO2 and sulfate aerosols (SA) from ground-based Fourier transform infrared (FTIR) observations. These effluents, both linked to magmatic degassing process and subsequent atmospheric evolution processes, have overlapping spectral signatures leading to mutual potential interferences when retrieving one species without considering the other. We show that significant overestimations may be introduced in SO2 retrievals if the radiative impact of coexistent SA is not accounted for, which may have impacted existing SO2 long-term series, e.g. from satellite platforms. The method was applied to proximal observations at Masaya volcano, where SO2 and SA concentrations, and SA acidity, were retrieved. A gas-to-particle sulfur partitioning of 400 and a strong SA acidity (sulfuric acid concentration: 65 %) were found, consistent with past in situ observations at this volcano. This method is easily exportable to other volcanoes to monitor magma extraction processes and the atmospheric sulfur cycle in the case of ash-free plumes.
Highlights
Volcanic gas and particulate emissions affect tropospheric and stratospheric compositions, air quality and the environment, the distribution and optical properties of low and high clouds, the Earth radiation budget from the regional to the global scale, and climate (e.g. von Glasow et al, 2009; Robock, 2000)
We demonstrate that systematic detection, quantification and chemical characterisation of volcanic sulfate aerosols using OP-Fourier transform infrared (FTIR) spectrometry is feasible
The raw FTIR observations for this spectrum are in the Supplement
Summary
Volcanic gas and particulate emissions affect tropospheric and stratospheric compositions, air quality and the environment, the distribution and optical properties of low and high clouds, the Earth radiation budget from the regional to the global scale, and climate (e.g. von Glasow et al, 2009; Robock, 2000). One of the most important environmental pollutants and the main source of radiative forcing from volcanoes is long-lived acidic and highly reflective sulfate aerosols (SA), directly emitted (primary SA) or formed by gas-to-particle conversion of sulfur dioxide (SO2) emissions (secondary SA). Observing these volcanic emissions and their atmospheric processes and variability in space and time using groundbased and satellite remote sensing is a crucial step towards understanding and quantifying their environmental and climatic impacts.
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