Vitchko Tsanev

Characterization and evolution of tropospheric plumes from Lascar and Villarrica volcanoes, Chile

Chile, reveal that both are significant and sustained emitters of SO2 (28 and 3.7 kg s � 1 , respectively), HCl (9.6 and 1.3 kg s � 1 , respectively), HF (4.5 and 0.3 kg s � 1 , respectively) and near-source sulfate aerosol (0.5 and 0.1 kg s � 1 , respectively). Aerosol plumes are characterized by particle number fluxes (0.08–4.0 mm radius) of � 10 17 s � 1 (Lascar) and � 10 16 s � 1 (Villarrica), the majority of which will act as cloud condensation nuclei at supersaturations >0.1%. Impactor studies suggest that the majority of these particles contain soluble SO4� . Most aerosol size distributions were bimodal with maxima at radii of 0.1–0.2 mm and 0.7–1.5 mm. The mean particle effective radius (Reff) ranged from 0.1 to 1.5 mm, and particle size evolution during transport appears to be controlled by particle water uptake (Villarrica) or loss (Lascar) rather than sulfate production. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 8409 Volcanology: Atmospheric effects (0370); 8494 Volcanology: Instruments and techniques; KEYWORDS: volcanoes, degassing, aerosol sulphur dioxide, sulphate, Llaima

Ozone depletion in tropospheric volcanic plumes

Ground based remote sensing techniques are used to measure volcanic SO2 fluxes in efforts to characterise volcanic activity. As these measurements are made several km from source there is the potential for in-plume chemical transformation of SO2 to sulphate aerosol (conversion rates are dependent on meteorological conditions), complicating interpretation of observed SO2 flux trends. In contrast to anthropogenic plumes, SO2 lifetimes are poorly constrained for tropospheric volcanic plumes, where the few previous loss rate estimates vary widely (from 99% per hour). We report experiments conducted on the boundary layer plume of Masaya volcano, Nicaragua during the dry season. We found that SO2 fluxes showed negligible variation with plume age or diurnal variations in temperature, relative humidity and insolation, providing confirmation that remote SO2 flux measurements (typically of approximate to500-2000 s old plumes) are reliable proxies for source emissions for ash free tropospheric plumes not emitted into cloud or fog.

Observations of the plume generated by the December 2005 oil depot explosions and prolonged fire at Buncefield (Hertfordshire, UK) and associated atmospheric changes

The explosions and subsequent fire at the Buncefield oil depot in December 2005 afforded a rare opportunity to study the atmospheric consequences of a major oil fire at close range, using ground-based remote-sensing instruments. Near-source measurements (less than 10 km) suggest that plume particles were approximately 50% black carbon (BC) with refractive index 1.73−0.42i, effective radius (Reff) 0.45–0.85 μm and mass loading approximately 2000 μg m−3. About 50 km downwind, particles were approximately 60–75% BC with refractive index between 1.80−0.52i and 1.89−0.69i, Reff∼1.0 μm and mass loadings 320–780 μg m−3. Number distributions were almost all monomodal with peak at r<0.1 μm. Near-source UV spectroscopy revealed elevated trace gas concentrations of SO2 (70 ppbv), NO2 (140 ppbv), HONO (20 ppbv), HCHO (160 ppbv) and CS2 (40 ppbv). Our measurements are consistent with others of the Buncefield plume, and with studies of the 1991 Kuwaiti oil-fire plumes; differences from the latter reflecting in part contrasts in combustion efficiency and source composition (refined fuels versus crude oils) leading to important potential differences in atmospheric impacts. Other measurements made as the plume passed overhead approximately 50 km downwind showed a reduced solar flux reaching the surface, but little effect on the atmospheric potential gradient (electric field). The wind speed data from the day of the explosion hint at a possible explosion signature.

Reactive halogens (BrO and OClO) detected in the plume of Soufrière Hills Volcano during an eruption hiatus

Volcanic plumes are sites of dynamic chemistry involving halogen gases. Here we present new data on the relative abundances of SO2, BrO and OClO gases emitted from Soufriere Hills Volcano [SHV). They were collected during an eruptive hiatus but during sustained degassing at this halogen-rich volcano. By comparison with data from a previous study during an eruptive phase and application of the data and modeling of Villemant et al. (2008), we suggest that, after consideration of errors, either the rate of HBr conversion to BrO is variable, ranging from ∼30% to ∼15%, and/or the relative partitioning of Cl and Br into the gas phase from the melt changes according to eruptive activity. We examine the potential implications of this for fluid-melt partitioning, and compare our results with data from the experimental literature. Our work contributes toward understanding the controls on the BrO/SO2 ratio for volcano monitoring purposes; the changes in plume chemistry with regard to bromine at the onset of lava extrusion may be large and rapid. OClO was detected in the plume at SHV for the first time. This species has only previously been detected in emissions from Mount Etna (using ground-based methods) and from Puyehue Cordon Caulle (using satellite-based methods). No HCHO or NOy species were detected in the spectra.

Correlation between SO2 emissions rate and S contained in fuel used in a power plant, Noumea, New Caledonia

SO2 emissions from fossil fuel power plants can have significant impacts on human health and ecosystems. Consequently, numerous techniques are in use to monitor these emissions, in order to comply with environmental legislations. Here we highlight the correlation between SO2 emissions rate and the S contained in fuel used in power plant. We obtained a maximum of 1.3 kg.s-1 of SO2 emissions rate and a minimum of 0.4 kg.s-1 corresponding respectively to 2.9 % and 1.2 % of S contained in fuel. Measurements also indicate that high concentration of SO2 released from the Noumea 121 MW power plant is rapidly diluted in the first 10 minutes, corresponding to 3-4 km distance from the source downwind. Thus inhabitants living within the 3-4 km radius are potentially exposed to power plant emissions.