Spectroscopic measurements of volcanic gas emissions in the ultra-violet wavelength region

Abstract

In this thesis, three new remote sensing instruments were designed and applied to characterize volcanic gas plumes: a passive scanning differential optical absorption spectrometer (DOAS), an active Long-Path DOAS, and an SO2-camera. Using the passive DOAS, sulfur dioxide (SO2) emission fluxes were successfully quantified at 6 volcanoes. At Kilauea (Hawaii), e.g., elevated fluxes were measured in March 2008, an indication of an upcoming eruption which occurred just weeks later. Halogen chemistry in volcanic plumes was also studied. Bromine monoxide (BrO) was positively detected at Stromboli (Italy), Popocatepetl (Mexico) and Masaya (Nicaragua) volcanoes. By applying an active DOAS system to volcanoes for the first time, BrO measurements were conducted at night at Masaya. A distinct diurnal cycle was found in which the highest concentrations were present around local noon while they were below the detection limit at night, a strong indication that BrO is photochemically formed in volcanic plumes. Finally, radiative transfer modeling was used to simulate the optical paths of photons during passive remote sensing measurements. The results show that an inaccurate assessment of radiative transfer can induce large errors in these measurements. A correction algorithm is presented that for the first time allows the retrieval of aerosol conditions in volcanic plumes from DOAS measurements.