SO2 Emission Rates Research Articles

Air quality assessment in and around coal washery complexes using interval type-2 fuzzy reasoning approach

This paper presents a model based on interval type-2 fuzzy reasoning approach for assessment of air quality in coal washery complexes. In the proposed model, emission rates of SPM and SO2 from various sources and activities of coal washery complexes are estimated using fuzzy models. The presented models would be a pioneering work for the environmental researchers, engineers, policy makers and protection agencies to assess the impact of industrial activities in coal washery complexes. This approach would enable a better understanding of the pattern of environmental degradation through the sources and quantitatively assess to overcome the problem.

Measuring SO2 Emission Rates at Kīlauea Volcano, Hawaii, Using an Array of Upward-Looking UV Spectrometers, 2014–2017

The Hawaiian Volcano Observatory uses an array of ten fixed, upward-looking ultraviolet spectrometer systems to measure SO2 emission rates at 10-second sample intervals from the Kīlauea summit. We present Kīlauea SO2 emission rates from the volcano’s summit and Middle East Rift Zone during 2014-2017 and discuss the major sources of error for these measurements. Due to the wide range of SO2 emissions encountered at the summit vent, we used a variable wavelength spectral analysis range to accurately quantify both high and low SO2 column densities. We present case studies comparing the measured emission rates from the fixed spectrometer array to independent road and helicopter-based traverse measurements and evaluate the magnitudes and sources of uncertainties for each method. To address the challenge of obtaining accurate plume speed measurements, we examine ground-based wind-speed, plume speed tracking via spectrometer, and SO2 camera derived plume speeds. Our analysis shows that 1) the summit array column densities calculated using a dual fit window, are within -6 to +22% of results obtained with a variety of other conventional and experimental retrieval methods 2) emission rates calculated from the summit array located ~3 km downwind of the Overlook vent provide the best, practical estimate of summit SO2 release under normal trade wind conditions 3) ground-based anemometer wind speeds are 22% less than plume speeds determined by cross-correlation of plume features 4) our best estimate of average Kīlauea SO2 release for 2014-2017 is 5100 t/d, which is comparable to the space-based OMI emissions of 5518 t/d 5) short-term variability of SO2 emissions reflect Kīlauea lava lake dynamics.

Policies to promote energy efficiency and air emissions reductions in China's electric power generation sector during the 11th and 12th five-year plan periods: Achievements, remaining challenges, and opportunities

This paper reviews China’s achievements in energy efficiency improvements and air emissions reductions from the electric power sector during the 11th five-year plan (FYP) (2006–2010) and 12th FYP (2011–2015) periods, and discusses the remaining challenges and opportunities for policy formulation. Mandates for closure of small coal-fired power plants (CFPPs), and replacement with large ones, together with the promulgation of air emissions standards and the development of renewable energy projects, have resulted in an improvement of 15% in energy efficiency and a reduction of 91%, 89% and 96% in emission rates of SO2, NOx and PM from China’s electric power sector over the last decade. Compared to the United States, the Chinese electric power generation fleet is more energy efficient and has lower average emissions rates of SO2 and NOx. Despite these achievements, two characteristics of the current system pose serious challenges for China’s clean power development: a) two thirds of China’s power generation still rely on coal, and more CFPPs are being built and approved to be built; and b) high curtailment of renewable energy limits its benefits. We review the root causes of these challenges and highlight opportunities for enacting policies to address them.

Coupling Between Magmatic Degassing and Volcanic Tremor in Basaltic Volcanism

Magmatic degassing, typically measured as SO2 flux, plays a key role in controlling volcanic eruption style and is one of the key parameters used by volcano observatories to assess volcanic unrest and detect eruption precursors. Volcanic tremor, the integrated amplitude of seismic energy release over a range of frequencies, is also a key parameter in volcano monitoring. A connection between volcanic degassing and tremor has been inferred through correlations between the signals which are often, but not always, observed during periods of unrest or eruption. However, data are often equivocal and our understanding of the physical processes, which couple degassing with tremor are still evolving. New insights into degassing-tremor coupling can be made by investigation of the long-term relationship between degassing and tremor, focussing on the frequency-dependence of tremor and passive degassing behaviour. In this study, we examine how long-term SO2 emission rates and volcanic tremor on Mt. Etna, track rapid variability in eruptive dynamics. Correlations between SO2 flux and tremor are explored in both quiescent and eruptive periods, comparing the two parameters at both long and short time-scales (<< 1 day) for ~2 years. Our analysis reveals that over month-long timescales passive degassing of SO2 and tremor tend to be well-correlated, but these correlations are lost over shorter timescales. This reflects a coupling process between passive degassing and tremor, produced by a combination of gas flow through permeable magma and the convective flow of magma within the conduit. Short-term correlations are lost because variations in the continuous degassing process are relatively small compared with the overall degassing rate and fall below measurement noise..During eruptive periods strong correlations are observed between degassing and tremor, with a greater contribution of higher frequency signal in tremor, controlled by eruptive style. These observations suggest that in sin-eruptive periods the tremor source is dominated by the coupling between the eruption column and the ground through infrasonic waves, rather than conduit processes. Our results demonstrate the importance of high quality long-term observations and offer new insights into the physical mechanisms which couple degassing and volcanic tremor at active volcanoes.

Persistent growth of a young andesite lava cone: Bagana volcano, Papua New Guinea

Bagana, an andesite lava cone on Bougainville Island, Papua New Guinea, is thought to be a very young central volcano. We have tested this idea by estimating the volumes of lava extruded over different time intervals (1-, 2-, 3-, 9-, 15-, 70-years) using digital elevation models (DEMs), mainly created from satellite data. Our results show that the long-term extrusion rate at Bagana, measured over years to decades, has remained at about 1.0m3s−1. We present models of the total edifice volume, and show that, if our measured extrusion rates are representative, the volcano could have been built in only ~300years. It could also possibly have been built at a slower rate during a longer, earlier period of growth. Six kilometres NNW of Bagana, an andesite-dacite volcano, Billy Mitchell, had a large, caldera-forming plinian eruption 437years ago. We consider the possibility that, as a result of this eruption, the magma supply was diverted from Billy Mitchell to Bagana. It seems that Bagana is a rare example of a very youthful, polygenetic, andesite volcano. The characteristics of such a volcano, based on the example of Bagana, are: a preponderance of lava products over pyroclastic products, a high rate of lava extrusion maintained for decades, a very high rate of SO2 emission, evidence of magma batch fractionation and location in a trans-tensional setting at the end of an arc segment above a very steeply dipping and rapidly converging subduction zone.

Improved optical flow velocity analysis in SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; camera images of volcanic plumes – implications for emission-rate retrievals investigated at Mt Etna, Italy and Guallatiri, Chile

Abstract. Accurate gas velocity measurements in emission plumes are highly desirable for various atmospheric remote sensing applications. The imaging technique of UV SO2 cameras is commonly used to monitor SO2 emissions from volcanoes and anthropogenic sources (e.g. power plants, ships). The camera systems capture the emission plumes at high spatial and temporal resolution. This allows the gas velocities in the plume to be retrieved directly from the images. The latter can be measured at a pixel level using optical flow (OF) algorithms. This is particularly advantageous under turbulent plume conditions. However, OF algorithms intrinsically rely on contrast in the images and often fail to detect motion in low-contrast image areas. We present a new method to identify ill-constrained OF motion vectors and replace them using the local average velocity vector. The latter is derived based on histograms of the retrieved OF motion fields. The new method is applied to two example data sets recorded at Mt Etna (Italy) and Guallatiri (Chile). We show that in many cases, the uncorrected OF yields significantly underestimated SO2 emission rates. We further show that our proposed correction can account for this and that it significantly improves the reliability of optical-flow-based gas velocity retrievals. In the case of Mt Etna, the SO2 emissions of the north-eastern crater are investigated. The corrected SO2 emission rates range between 4.8 and 10.7 kg s−1 (average of 7.1 ± 1.3 kg s−1) and are in good agreement with previously reported values. For the Guallatiri data, the emissions of the central crater and a fumarolic field are investigated. The retrieved SO2 emission rates are between 0.5 and 2.9 kg s−1 (average of 1.3 ± 0.5 kg s−1) and provide the first report of SO2 emissions from this remotely located and inaccessible volcano.

Performance and Emissions Control of Commercial-Scale Biochar Production Unit

Abstract.Two commercial biochar production machines – a single-auger unit and a larger dual-auger version – were operated to evaluate feedstock specifications, biochar quality, throughput rates, and emissions profiles. Biochar was produced from woody biomass feedstocks of various species, contamination levels, comminution methods, and moisture contents. Feedstocks with ash content exceeding 15% dry basis or moisture content exceeding 25% wet basis were observed to decrease fixed carbon content of biochar and to increase the labor effort required to operate the machine. The dual-auger version of the machine was able to process 380 kg h-1 of biomass feedstock (dry basis) to produce 63 kg h-1 of biochar with a mean electricity demand of 4.5 kW. Average CO, propane, NOx, and SO2 emission rates from the flare of this machine were measured to be 160, 120, 51, and 43 g h-1, respectively, with total particulate matter (PM), PM10, and PM2.5 emission rates of 380, 40, and 4.5 g h-1, respectively. Results from these experiments indicate that high-quality biochar can be produced from a variety of feedstocks, including forest residuals, as long as the ash and moisture content are within the specifications. Future research and development should focus on increasing the throughput of the machine, implementing an automated control system to reduce the operational effort, and improving safety and product consistency. Keywords: Biochar, Biomass, Biomass conversion technology, Carbon sequestration, Forest residuals, Gasification, Pyrolysis.

Pyplis–A Python Software Toolbox for the Analysis of SO2 Camera Images for Emission Rate Retrievals from Point Sources

Ultraviolet (UV) SO2 cameras have become a common tool to measure and monitor SO2 emission rates, mostly from volcanoes but also from anthropogenic sources (e.g., power plants or ships). Over the past decade, the analysis of UV SO2 camera data has seen many improvements. As a result, for many of the required analysis steps, several alternatives exist today (e.g., cell vs. DOAS based camera calibration; optical flow vs. cross-correlation based gas-velocity retrieval). This inspired the development of Pyplis (Python plume imaging software), an open-source software toolbox written in Python 2.7, which unifies the most prevalent methods from literature within a single, cross-platform analysis framework. Pyplis comprises a vast collection of algorithms relevant for the analysis of UV SO2 camera data. These include several routines to retrieve plume background radiances as well as routines for cell and DOAS based camera calibration. The latter includes two independent methods to identify the DOAS field-of-view (FOV) within the camera images (based on (1) Pearson correlation and (2) IFR inversion method). Plume velocities can be retrieved using an optical flow algorithm as well as signal cross-correlation. Furthermore, Pyplis includes a routine to perform a first order correction of the signal dilution effect (also referred to as light dilution). All required geometrical calculations are performed within a 3D model environment allowing for distance retrievals to plume and local terrain features on a pixel basis. SO2 emission rates can be retrieved simultaneously for an arbitrary number of plume intersections. Hence, Pyplis provides a state-of-the-art framework for more efficient and flexible analyses of UV SO2 camera data and, therefore, marks an important step forward towards more transparency, reliability and inter-comparability of the results. Pyplis has been extensively and successfully tested using data from several field campaigns. Here, the main features are introduced using a dataset obtained at Mt. Etna, Italy on 16 September 2015.

Sensitivity of Aerosol Distribution and Climate Response to Stratospheric SO2 Injection Locations

AbstractInjection of SO2 into the stratosphere has been proposed as a method to, in part, counteract anthropogenic climate change. So far, most studies investigated injections at the equator or in a region in the tropics. Here we use Community Earth System Model version 1 Whole Atmosphere Community Climate Model (CESM1(WACCM)) to explore the impact of continuous single grid point SO2 injections at seven different latitudes and two altitudes in the stratosphere on aerosol distribution and climate. For each of the 14 locations, 3 different constant SO2 emission rates were tested to identify linearity in aerosol burden, aerosol optical depth, and climate effects. We found that injections at 15°N and 15°S and at 25 km altitude have equal or greater effect on radiation and surface temperature than injections at the equator. Nonequatorial injections transport SO2 and sulfate aerosols more efficiently into middle and high latitudes and result in particles of smaller effective radius and larger aerosol burden in middle and high latitudes. Injections at 15°S produce the largest increase in global average aerosol optical depth and increase the change in radiative forcing per Tg SO2/yr by about 15% compared to equatorial injections. High‐altitude injections at 15°N produce the largest reduction in global average temperature of 0.2° per Tg S/yr for the last 7 years of a 10 year experiment. Injections at higher altitude are generally more efficient at reducing surface temperature, with the exception of large equatorial injections of at least 12 Tg SO2/yr. These findings have important implications for designing a strategy to counteract global climate change.

Gas and ash emissions associated with the 2010–present activity of Sinabung Volcano, Indonesia

Sinabung Volcano (Sumatra, Indonesia) awoke from over 1200years of dormancy with multiple phreatic explosions in 2010. After a period of quiescence, Sinabung activity resumed in 2013, producing frequent explosions, lava dome extrusion, and pyroclastic flows from dome and lava flow collapses, becoming one of the world's most active volcanoes and displacing over 20,000 citizens. This study presents a compilation of the geochemical datasets collected by the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM) from 2010–current (2016), which provides insights into the evolution of the eruption. Based on observations of SO2 emissions, ash componentry, ash leachate chemistry, and bulk ash geochemistry, the eruption can be split into six distinct geochemical phases. The initial stage of phreatic summit explosions (phase A) occurred from August–September 2010, during which background SO2 emissions averaged ~550±180t/d (1s.d.). An eruptive pause (phase B) starting in October 2010 abruptly ended in September 2013 with a resumption of conduit-clearing eruptions (phase C). This third phase had a relatively modest background SO2 emission rate (avg. ~430±310t/d) and produced ash consisting of accidental ejecta with high S/Cl leachate molar ratios (12.0±8.2, max 34), suggestive of deep-sourced magma and/or the incorporation of hydrothermal sulfur-bearing phases. Lava extrusion at the summit (phase D) began in mid-December 2013, and was accompanied by relatively low SO2 emission rates (360±200t/d) and lower, but variable, S/Cl leachate ratios (6.3±8.5). The most intense phase of the eruption (phase E) occurred from mid-January to late February 2014 following a major lava dome collapse. This period included increased lava extrusion rates, dozens of large eruptions per day, high SO2 emission rates (average: 1680±1070t/d, peak: ~3800t/d), and a dramatic drop in S/Cl ash leachates to ratios (average 1.4±0.5), consistent with increased degassing from shallow magma and the clearing out of sulfurous phases from the old hydrothermal system. From March 2014 through the time of writing (September 2016), Sinabung settled into a relatively steady state of lower activity (phase F). Ash emissions now consist of dominantly juvenile andesitic-dacitic material with low S/Cl leachate ratios (average 1.1±0.6). In August 2016, SO2 emissions started being measured in a continuous manner using a network of permanent scanning DOAS instruments. Background SO2 emission rates average 450±290t/d for the entirety of phase F, but have been progressively decreasing to an average of ~250–300t/d since June 2016. This long-term gradual decline in SO2 emission rates at Sinabung since early 2014 is consistent with an apparent decrease in magma supply and lava effusion rates. Our conceptual degassing model suggests that large explosions and pyroclastic flows could continue in the near-term owing to conduit plugging and dome collapses, remaining a major threat until the magma supply rate decreases further and the eruption ends.

Computer vision for improved estimates of SO2 emission rates and plume dynamics

ABSTRACTImaging cameras operating at ultraviolet (UV) and infrared (IR) wavelengths can measure sulphur dioxide (SO2) gas path concentrations or slant column densities. These measurements are useful in a variety of applications including the monitoring of emissions from volcanoes and also emissions from stacks at industrial plants and on ships. The usefulness of these data is increased if the emission rates (or fluxes) of the gases can also be estimated. Here we present an optical flow algorithm that allows rapid and accurate estimates of emission rates using both UV and IR camera imagery sampling at around 1 Hz or higher. Examples are provided from measurements made at Turrialba volcano, Costa Rica, and also at a ship in Hong Kong harbour. Other aspects of the properties of the fluid flow are also introduced, notably the divergence and the vorticity of the two-dimensional wind field. We demonstrate how the divergence can be used in a new method to calculate the emission rate and show how rotational effects observed in volcanic plumes and the resulting entrainment of ambient air affects plume rise and can be observed using vorticity. This is an important aspect for understanding the emplacement of gases and particles into the atmosphere that are subsequently transported by atmospheric winds, sometimes causing pollution episodes at long distances from the source.

Volcanogenic SO2, a natural pollutant: Measurements, modeling and hazard assessment at Vulcano Island (Aeolian Archipelago, Italy)

Sulfur dioxide (SO2) is a major component of magmatic gas discharges. Once emitted in the atmosphere it can affect the air and land environment at different spatial and temporal scales, with harmful effects on human health and plant communities.We used a dense dataset of continuous SO2 flux and meteorological measurements collected at Vulcano over an 8-year period spanning from May 2008 to February 2016 to model air SO2 concentrations over the island. To this end, we adopted the DISGAS (DISpersion of GAS) numerical code coupled with the Diagnostic Wind Model (DWM). SO2 concentrations in air were determined for three different SO2 emission rates: a reference SO2 flux of ∼18 t/d (the median of more than 800 measurements), an enhanced SO2 flux of 40 t/d (average of all measurements plus 1 σ), and a maximum SO2 flux of 106 t/d (maximum value measured in the investigated period). Maximum SO2 concentrations in air were estimated at the crater, near the high-T fumarole field that is the source of the gas, and ranged from 2000 ppb to ∼24,000 ppb for the reference flux, from 2000 ppb to 51,000 ppb for the enhanced flux and from 5000 ppb to 136,000 ppb for the maximum flux, with peak values in limited areas at the bottom of the crater. These concentrations pose a hazard for people visiting the crater, for sensitive individuals in particular. Based on estimated SO2 concentrations in air, we also consider the phytotoxic effects of SO2 on local vegetation.

Long‐term monitoring of long‐period seismicity and space‐based SO2 observations at African lava lake volcanoes Nyiragongo and Nyamulagira (DR Congo)

AbstractMagma ascent that may lead to an eruption is commonly accompanied by variations of long‐period seismic activity and SO2 degassing. Space‐based measurements of SO2 emission rates represent a rapidly emerging and highly convenient approach for volcano monitoring; however, combining these long‐term remote sensing observations with seismic data is still rare and, in particular, the potential of such a multidisciplinary approach as volcano monitoring tool remains largely unexplored. Here shallow magmatic activity and magma migration patterns at the two closely located African volcanoes Nyiragongo and Nyamulagira are inferred from a nearly 3 years long SO2 emissions record and seismic observations between April 2014 and February 2017. The discrimination of magma movements into shallow plumbing systems allows for signs of volcanic unrest to be deciphered on a daily time scale, even with limited instrumentation on site.

Plume Segmentation from UV Camera Images for SO2 Emission Rate Quantification on Cloud Days

We performed measurements of SO2 emissions with a high UV sensitive dual-camera optical system. Generally, in order to retrieve the two-dimensional SO2 emission rates of a source, e.g., the slant column density of a plume emitted by a stack, one needs to acquire four images with UV cameras: two images including the emitting stack at wavelengths with high and negligible absorption features (λon/off), and two additional images of the background intensity behind the plume, at the same wavelengths as before. However, the true background intensity behind a plume is impossible to obtain from a remote measurement site at rest, and thus, one needs to find a way to approximate the background intensity. Some authors have presented methods to estimate the background behind the plume from two emission images. However, those works are restricted to dealing with clear sky, or almost homogeneously illuminated days. The purpose of this work is to present a new approach using background images constructed from emission images by an automatic plume segmentation and interpolation procedure, in order to estimate the light intensity behind the plume. We compare the performance of the proposed approach with the four images method, which uses, as background, sky images acquired at a different viewing direction. The first step of the proposed approach involves the segmentation of the SO2 plume from the background. In clear sky days, we found similar results from both methods. However, when the illumination of the sky is non homogeneous, e.g., due to lateral sun illumination or clouds, there are appreciable differences between the results obtained by both methods. We present results obtained in a series of measurements of SO2 emissions performed on a cloudy day from a stack of an oil refinery in Montevideo City, Uruguay. The results obtained with the UV cameras were compared with scanning DOAS measurements, yielding a good agreement.

On the use of different spectral windows in DOAS evaluations: Effects on the estimation of SO2 emission rate and mixing ratios during strong emission of Popocatépetl volcano

Reported SO2 emission values at strongly degassing volcanoes might be underestimated. Scanning spectroscopic instruments are widely used at volcanoes to quantify SO2 emission rates and, occasionally, molar ratios between SO2 and other gases such as BrO. Frequently, Differential Optical Absorption Spectroscopy is applied to evaluate spectra in the ultraviolet range. If radiative transfer effects are not considered in the evaluations, the retrieved column densities may vary depending on which spectral window is used. We compare the use of different windows for data collected at Popocatépetl volcano during strong degassing periods, when high column densities lead to especially high dependence on the applied evaluation window. We propose the use of three different windows (310–322nm, 314.7–326.7nm and 322–334nm) and a simple algorithm to choose the most accurate column density from them. The SO2 evaluation using proper spectral windows would allow a more realistic estimation of the SO2 emission rates.

The quantification of atmospheric emissions from complex configuration sources using reverse dispersion modelling

Reverse dispersion modelling was employed to quantify sulphur dioxide (SO2) and nitrogen dioxide (NO2) emissions from brick firing clamp kilns and spontaneous combustion from a coal discard dump. Reverse dispersion modelling technique integrates ambient monitoring and dispersion simulation to calculate actual emission rates from an assumed rate of 1 g per second (g/s). Emission rates and emission factors were successfully quantified for SO2, but not for NO2, due to the influence of external sources and the complexity regarding the varying proportion of nitrogen oxides released from the kiln. Quantified emission factor for clamp kiln firing ranged from 1.91–3.24 g of SO2 per brick fired and 0.67–1.14 g of SO2 per kilogram of bricks fired. The variation in SO2 emission factors was linked to high variability in energy input. The source configuration input to the dispersion model, assumed to represent the kiln, was changed from a volume source to a more effective “bi-point” source situated at the top of the kiln, with buoyancy calculated from the carbon combustion rate. In addition, SO2 emission rate for spontaneous combustion from the discard dump was quantified as 0.35 g/s. 274 tons of discard material was estimated to burn annually, assuming that the emission rate is consistent over a year. Consequently, the reverse dispersion modelling and the elevated “bi-point” source technique may be considered a novel approach for quantifying emissions from combustion of materials or mixture of materials where knowledge of source parameters is limited.

Magmatic degassing, lava dome extrusion, and explosions from Mount Cleveland volcano, Alaska, 2011–2015: Insight into the continuous nature of volcanic activity over multi-year timescales

Mount Cleveland volcano (1730m) is one of the most active volcanoes in the Aleutian arc, Alaska, but heightened activity is rarely accompanied by geophysical signals, which makes interpretation of the activity difficult. In this study, we combine volcanic gas emissions measured for the first time in August 2015 with longer-term measurements of thermal output and lava extrusion rates between 2011 and 2015 calculated from MODIS satellite data with the aim to develop a better understanding of the nature of volcanic activity at Mount Cleveland. Degassing measurements were made in the month following two explosive events (21 July and 7 August 2015) and during a period of new dome growth in the summit crater. SO2 emission rates ranged from 400 to 860td−1 and CO2/SO2 ratios were <3, consistent with the presence of shallow magma in the conduit and the observed growth of a new lava dome. Thermal anomalies derived from MODIS data from 2011 to 2015 had an average repose time of only 4days, pointing to the continuous nature of volcanic activity at this volcano. Rapid increases in the cumulative thermal output were often coincident with visual confirmation of dome growth or accumulations of tephra in the crater. The average rate of lava extrusion calculated for 9 periods of rapid increase in thermal output was 0.28m3s−1, and the total volume extruded from 2011 to 2015 was 1.9–5.8Mm3. The thermal output from the lava extrusion events only accounts for roughly half of the thermal budget, suggesting a continued presence of shallow magma in the upper conduit, likely driven by convection. Axisymmetric dome morphology and occasional drain back of lava into the conduit suggests low-viscosity magmas drive volcanism at Mount Cleveland. It follows also that only small overpressures can be maintained given the small domes and fluid magmas, which is consistent with the low explosivity of most of Mount Cleveland's eruptions. Changes between phases of dome growth and explosive activity are somewhat unpredictable and likely result from plugs that are related to the dome obtaining a critical dimension, or from small variations in the magma ascent rate that lead to crystallization-induced blockages in the upper conduit, thereby reducing the ability of magma to degas. We suggest the small magma volumes, slow ascent rates, and low magma viscosity lead to the overall lack of anomalous geophysical signals prior to eruptions, and that more continuous volcanic degassing measurements might lead to more successful eruption forecasting at this continuously-active open-vent volcano.

Volcanic gas composition changes during the gradual decrease of the gigantic degassing activity of Miyakejima volcano, Japan, 2000-2015

The composition of volcanic gases discharged from Miyakejima volcano has been monitored during the intensive degassing activity that began after the eruption in 2000. During the 15 years from 2000 to 2015, Miyakejima volcano discharged 25.5 Mt of SO2, which required degassing of 3 km3 of basaltic magma. The SO2 emission rate peaked at 50 kt/day at the end of 2000 and quickly decreased to 5 kt/day by 2003. During the early degassing period, the volcanic gas composition was constant with the CO2/SO2 = 0.8 (mol ratio), H2O/SO2 = 35, HCl/SO2 = 0.08, and SO2/H2S = 15. The SO2 emission rate decreased gradually to 0.5 kt/day by 2012, and the gas composition also changed gradually to CO2/SO2 = 1.5, H2O/SO2 = 150, HCl/SO2 = 0.15, and SO2/H2S = 6. The compositional changes are not likely caused by changes in degassing pressure or volatile heterogeneity of a magma chamber but are likely attributed to an increase of hydrothermal scrubbing caused by large decrease of the volcanic gas emission rate, suggesting a supply of gases with constant composition during the 15 years. The intensive degassing was modeled based on degassing of a convecting magma conduit. The gradual SO2 emission rate that decrease without changes in volcanic gas composition is attributed to a reduction of diameter of the convecting magma conduit.

Retrieval of absolute SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks

Abstract. Scanning spectrometer networks using scattered solar radiation in the ultraviolet spectral region have become an increasingly important tool for monitoring volcanic sulfur dioxide (SO2) emissions. Often measured spectra are evaluated using the differential optical absorption spectroscopy (DOAS) technique. In order to obtain absolute column densities (CDs), the DOAS evaluation requires a Fraunhofer reference spectrum (FRS) that is free of absorption structures of the trace gas of interest. For measurements at volcanoes such a FRS can be readily obtained if the scan (i.e. series of measurements at different elevation angles) includes viewing directions where the plume is not seen. In this case, it is possible to use these viewing directions (e.g. zenith) as FRS. Possible contaminations of the FRS by the plume can then be corrected by calculating and subtracting an SO2 offset (e.g. the lowest SO2 CD) from all viewing directions of the respective scan. This procedure is followed in the standard evaluations of data from the Network for Observation of Volcanic and Atmospheric Change (NOVAC). While this procedure is very efficient in removing Fraunhofer structures and instrumental effects it has the disadvantage that one can never be sure that there is no SO2 from the plume in the FRS. Therefore, using a modelled FRS (based on a high-resolution solar atlas) has a great advantage. We followed this approach and investigated an SO2 retrieval algorithm using a modelled FRS. In this paper, we present results from two volcanoes that are monitored by NOVAC stations and which frequently emit large volcanic plumes: Nevado del Ruiz (Colombia) recorded between January 2010 and June 2012 and from Tungurahua (Ecuador) recorded between January 2009 and December 2011. Instrumental effects were identified with help of a principal component analysis (PCA) of the residual structures of the DOAS evaluation. The SO2 retrieval performed extraordinarily well with an SO2 DOAS retrieval error of 1 − 2 × 1016 [molecules cm−2]. Compared to a standard evaluation, we found systematic differences of the differential slant column density (dSCD) of only up to ≈ 15 % when looking at the variation of the SO2 within one scan. The major advantage of our new retrieval is that it yields absolute SO2 CDs and that it does not require complicated instrumental calibration in the field (e.g. by employing calibration cells or broadband light sources), since the method exploits the information available in the measurements.We compared our method to an evaluation that is similar to the NOVAC approach, where a spectrum that is recorded directly before the scan is used as an FRS and an SO2 CD offset is subtracted from all retrieved dSCD in the scan to correct for possible SO2 contamination of the FRS. The investigation showed that 21.4 % of the scans (containing significant amounts of SO2) at Nevado del Ruiz and 7 % of the scans at Tungurahua showed much larger SO2 CDs when evaluated using modelled FRS (more than a factor of 2). For standard evaluations the overall distribution of the SO2 CDs in a scan can in some cases indicate whether the plume affects all viewing directions and thus these scans need to be discarded for NOVAC emission rate evaluation. However, there are other cases where this is not possible and thus the reported SO2 emission rates would be underestimated. The new method can be used to identify these cases and thus it can considerably improve SO2 emission budgets.

Pre‐eruptive inflation caused by gas accumulation: Insight from detailed gas flux variation at Sakurajima volcano, Japan

AbstractSulfur dioxide (SO2) emission rate observations were made at Sakurajima volcano, Japan, to quantify the relationship between the SO2 emission rate and inflation prior to Vulcanian explosions. The explosions associated with precursory inflation events were preceded by decreases in SO2 emission rates by 10–60 min. The amounts of accumulated gas were calculated using time series of SO2 emission rate. The amounts of accumulated SO2 and increases in strain records before the explosions showed a positive correlation. The volume increase of a deformation source calculated using the strain records was of the comparable order of magnitude as the volume of the accumulated volcanic gas. The results suggest that the inflations before the explosions were caused by the gas accumulation.