On bromine, nitrogen oxides and ozone depletion in the tropospheric plume of Erebus volcano (Antarctica)

International audienceSince the discovery of bromine oxide (BrO) in volcanic emissions, there has been speculation concerning its role in chemical evolution and notably ozone depletion in volcanic plumes. We report the first measurements using Differential Optical Absorption Spectroscopy (DOAS) of BrO in the tropospheric plume of the persistently degassing Erebus volcano (Antarctica). These are the first observations pertaining to emissions from an alkaline phonolitic magma. The observed BrO/SO2 ratio of 2.5 x 10-4 is similar to that measured at andesitic arc volcanoes. The high abundance of BrO is consistent with high abundances of F and Cl relative to sulfur in the Erebus plume. Our estimations of HBr flux and BrO production rate suggest that reactive bromine chemistry can explain a 35% loss of tropospheric O3 observed in the Erebus plume at approximately 30 km from source (Oppenheimer et al., 2010). Erebus also has a permanent lava lake, which could result in generation of NOx by thermal fixation of atmospheric N2 at the hot lava surface. Any NOx emission could play a potent role in reactive bromine chemistry. However, the presence of NO2 could not be detected in the plume, about 400 m above the lake, in our DOAS observations of 2005. Nor could we reproduce spectroscopic retrievals that reportedly identified NO2 in DOAS observations from 2003 made of the Erebus plume (Oppenheimer et al., 2005). Based on the NO2 detection limit of our analysis, we can state an upper limit of the NO2/SO2 ratio of ≤ 0.012, an order of magnitude lower than previously reported. Our new result supports a rapid oxidation of NOx in the young plume and is more consistent with measurements of NOy species measured using an instrumented aircraft flying in the plume. Model simulations, tuned for Erebus, were performed to reproduce the BrO/SO2 observed in the young plume and to investigate the impact of NOx emissions at source on the subsequent formation of BrO in the plume. They support our hypothesis of rapid conversion of NOx to NOy in the vicinity of the lava lake. This study thus places new constraints on the interaction between reactive nitrogen and bromine species in volcanic plumes, and its effects on ozone

A re-assessment of aerosol size distributions from Masaya volcano (Nicaragua)

International audienceCascade impactors were used to sample volcanic aerosol from Masaya (Nicaragua) in 2007, 2009 and 2010. Differences were found in the size distributions of volcanic aerosol between these recent campaigns and with a campaign in 2001: (1) SO42− showed modes in both the fine (1 μm; with high Na+/K+) fractions in all of the recent campaigns despite being unimodal in 2001 (<1 μm); (2) The modal diameters for SO42− roughly doubled in 2009, compared to 2007 or 2010; (3) total Cl− was depleted in volcanic aerosol compared to background aerosol in all the more recent campaigns but was enriched in 2001. Other aspects of the volcanic aerosol appear to be persistent, such as a fine SO42−-H+-Na+-K+ mode, which was the most abundant mode in all campaigns, and a coarse Cl−-F−-Mg2+-Ca2+ mode of lower abundance. Water uptake and speciation in the aerosol were investigated using the equilibrium model, ISORROPIA II. Results show that the coarse SO42−-rich mode deliquesces at lower relative humidity (40% RH) than the fine SO42−-rich mode (50% RH) due to increased Na+/K+ in the former. The aerosol was predicted to be dry at ambient relative humidity in 2009 and dominated by NaHSO4, KHSO4, CaSO4 and MgSO4. In contrast, model results predict a liquid aerosol at ambient relative humidity in 2010. These results indicate that aerosol emissions from a volcano can vary in ionic composition and even more so in physical speciation (i.e., salts or solutions). These observations are set against a near-constant magmatic gas composition at Masaya, which highlights the significance of atmospheric and dynamic factors in the formation of volcanic aerosols

Near-source observations of aerosol size distributions in the eruptive plumes from Eyjafjallajökull volcano, March-April 2010

Near-source observations of aerosol size distributions (<15 km from the vent) were made during three eruptive phases of Eyjafjallajökull in 2010: Phase I - basaltic lava fountaining; Phase II - andesitic phreatomagmatic explosions (mass discharge rate of the order of 105 kg s-1); Phase III - andesitic magmatic explosions (mass discharge rate of the order of 103 kg s-1). Two methods were used, photometric measurements of suspended aerosol mass (with size distributions retrieved by inverse modelling); and sampling of ash fallout during Phases II and III (with size distributions measured by laser diffraction). The suspended aerosol in Phase I plume was dominated by particles sized <0.4 [mu]m in diameter. During Phase II, the suspended aerosol mass contained a high number of fine (<1 [mu]m) particles (an internal mixture of soluble aerosol and very fine ash) and coarse (>1 [mu]m) ash particles. The number ratio of fine and coarse particles fluctuated strongly within short intervals of time, indicative of changes in the fragmentation energy. The near-source ash fallout was poorly sorted (interquartile range 16-80 [mu]m); ash grains sized <1 [mu]m contributed up to 7% of total volume. The high water content and electrical charge in the plume are believed to have enhanced the deposition through particle aggregation. In Phase III the eruption became drier and less explosive. The suspended aerosol mass was strongly bimodal with high particle abundances at ~0.2 and 1-4 [mu]m. The ash fallout was better sorted (interquartile range 60-120 [mu]m; no grains <1 [mu]m), attributed to limited particle aggregation

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 10km) suggest that plume particles were approximately 50% black carbon (BC) with refractive index 1.73-0.42i, effective radius (Reff) 0.45-0.85μm and mass loading approximately 2000μgm-3. About 50km downwind, particles were approximately 60-75% BC with refractive index between 1.80-0.52i and 1.89-0.69i, R eff∼1.0μm and mass loadings 320-780μgm-3. Number distributions were almost all monomodal with peak at r&lt;0.1μm. Near-source UV spectroscopy revealed elevated trace gas concentrations of SO2 (70ppbv), NO2 (140ppbv), HONO (20ppbv), HCHO (160ppbv) and CS 2 (40ppbv). 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 50km 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. © 2007 The Royal Society

Size distributions of fine silicate and other particles in Masaya's volcanic plume.

Direct-sampling and remote-sensing measurements were made at the crater rim of Masaya volcano (Nicaragua) to sample the aerosol plume emanating from the active vent. We report the first measurements of the size distribution of fine silicate particles (d <10 mu m) in Masaya's plume, by automated scanning electron microscopy (QEMSCAN) analysis of a particle filter. The particle size distribution was approximately lognormal with modal d similar to 1.15 mu m. The majority of these particles were found to be spherical. These particles are interpreted to be droplets of quenched magma produced by a spattering process. Compositional analyses confirm earlier reports that the fine silicate particles show a range of compositions between that of the degassing magma and nearly pure silica and that the extent of compositional variability decreases with increasing particle size. These results indicate that fine silicate particles are altered owing to reactions with acidic droplets in the plume. The emission flux of fine silicate particles was estimated as similar to 10(11) s(-1), equivalent to similar to 55 kg d(-1). Sun photometry, aerosol spectrometry, and thermal precipitation were used to determine the overall particle size distribution of the plume (0.01 < d(mu m) < 10). Sun photometry and aerosol spectrometry measurements indicate the presence of a large number of particles (assumed to be aqueous) with d similar to 1 mu m. Aerosol spectrometry measurements further show an increase in particle size as the nighttime approached. The emission flux of particles from Masaya was estimated as similar to 10(17) s(-1), equivalent to similar to 5.5 Mg d(-1) where d < 4 mu m

Near-source observations of aerosol size distributions in the eruptive plumes from Eyjafjallajökull volcano, March-April 2010

Near-source observations of aerosol size distributions (1 [mu]m) ash particles. The number ratio of fine and coarse particles fluctuated strongly within short intervals of time, indicative of changes in the fragmentation energy. The near-source ash fallout was poorly sorted (interquartile range 16-80 [mu]m); ash grains sized <1 [mu]m contributed up to 7% of total volume. The high water content and electrical charge in the plume are believed to have enhanced the deposition through particle aggregation. In Phase III the eruption became drier and less explosive. The suspended aerosol mass was strongly bimodal with high particle abundances at ~0.2 and 1-4 [mu]m. The ash fallout was better sorted (interquartile range 60-120 [mu]m; no grains <1 [mu]m), attributed to limited particle aggregation

Surge in sulphur and halogen degassing from Ambrym volcano, Vanuatu

Volcanoes provide important contributions to atmospheric budgets of SO2 and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January 2005 indicate fluxes of 18-270 kg s-1 of SO2, and 62-110 gs-1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on Earth. We also estimate high Cl and F fluxes of ~8-14 and ~27-50 kg s-1, respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating SO2 output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single passively degassing volcano can make to the atmospheric budget of sulfur and halogens. © 2009 Springer-Verlag

Gas and aerosol emissions from Villarrica volcano, Chile

Here we report results from a multidisciplinary field campaign at Villarrica volcano, Chile, in March 2009. A range of direct sampling and remote sensing techniques was employed to assess gas and aerosol emissions from the volcano, and extend the time series of measurements that have been made during recent years. Airborne traverses beneath the plume with an ultraviolet spectrometer yielded an average SO2 flux of 3.7 kg s− 1. This value is similar to previous measurements made at Villarrica during periods of quiescent activity. The composition of the plume was measured at the crater rim using electrochemical sensors and, for the first time, open-path Fourier transform infrared spectroscopy, yielding a composition of 90.5 mol% H2O, 5.7% CO2, 2.6% SO2, 0.9% HCl, 0.3% HF and < 0.01% H2S. Comparison with previous gas measurements made between 2000 and 2004 shows a correlation between increased SO2/HCl ratios and periods of increased activity. Base-treated filter packs were also employed during our campaign, yielding molar ratios of HBr/SO2 = 1.1 × 10− 4, HI/SO2 = 1.4 × 10− 5 and HNO3/SO2 = 1.1 × 10−3 in the gas phase. Our data represent the most comprehensive gas inventory at Villarrica to date, and the first evaluation of HBr and HI emissions from a South American volcano. Sun photometry of the plume showed the near-source aerosol size distributions were bimodal with maxima at < 0.1 and ~ 1 μm. These findings are consistent with results from analyses in 2003. Electron microscope analysis of particulate matter collected on filters showed an abundance of spherical micron-sized particles that are rich in Si, Mg and Al. Non-spherical, S-rich particles were also observed