Technological advances to improve the quantification of volcanic emissions

Variations in volcanic trace gas composition and fluxes are a valuable indicator for changes in magmatic systems and therefore allow monitoring of the volcanic activity. An established method to measure trace gas emissions is to use remote sensing techniques like, for example, Differential Optical Absorption Spectroscopy (DOAS) and more recently SO₂-cameras, that can quantify volcanic sulphur dioxide (SO₂) emissions during quiescent degassing and eruptive phases, making it possible to correlate fluxes with volcanic activity. 

We present flux measurements of volcanic SO₂ emissions based on the novel remote sensing technique of Imaging Fabry-Pérot Interferometer Correlation Spectroscopy (IFPICS) in the UV spectral range. The basic principle of IFPICS lies in the application of an Fabry-Pérot Interferometer (FPI) as wavelength selective element. The FPIs periodic transmission profile is matched to the periodic spectral absorption features of SO₂, resulting in high spectral information for its detection. This technique yields a higher trace gas selectivity and sensitivity than imaging approaches based on interference filters, e.g. SO₂-cameras and an increased spatio-temporal resolution over spectroscopic imaging techniques, e.g. imaging DOAS. Hence, IFPICS shows reduced cross sensitivities to broadband absorption (e.g. to ozone, aerosols), which allows the application to weaker volcanic SO₂ emitters and increases the range of possible atmospheric conditions. It further raises the possibility to apply IFPICS to other trace gas species like, for example, bromine monoxide, that still can be characterized with a high spatial and temporal resolution (< 1 HZ).

In October 2020, we acquired SO₂ column density distribution images of Mt Etna volcanic plume with a detection limit of 2x10¹⁷ molec cm^-2, 1 s integration time, 400x400 pixel spatial, and 0.3 Hz temporal resolution.  We compare the SO₂ fluxes retrieved by IFPICS with simultaneous flux measurements using the mutli-axis DOAS technique.