SO2 Column Density Research Articles

Version 1 NOAA-20/OMPS Nadir Mapper total column SO2 product: continuation of NASA long-term global data record

Abstract. For nearly 2 decades, the Ozone Monitoring Instrument (OMI) aboard the NASA Aura spacecraft (launched in 2004) and the Ozone Mapping and Profiler Suite (OMPS) aboard the NASA/NOAA Suomi National Polar-orbiting Partnership (SNPP) satellite (launched in 2011) have been providing global monitoring of SO2 column densities from both anthropogenic and volcanic activities. Here, we describe the version-1 NOAA-20 (N20)/OMPS SO2 product (https://doi.org/10.5067/OMPS/OMPS_N20_NMSO2_PCA_L2_Step1.1, Li et al., 2023), aimed at extending the long-term climate data record. To achieve this goal, we apply a principal component analysis (PCA) retrieval technique, also used for the OMI and SNPP/OMPS SO2 products, to N20/OMPS. For volcanic SO2 retrievals, the algorithm is identical between N20 and SNPP/OMPS and produces consistent retrievals for eruptions such as Kilauea in 2018 and Raikoke in 2019. For anthropogenic SO2 retrievals, the algorithm has been customized for N20/OMPS, considering its greater spatial resolution and reduced signal-to-noise ratio as compared with SNPP/OMPS. Over background areas, N20/OMPS SO2 slant column densities (SCDs) show relatively small biases, comparable retrieval noise with SNPP/OMPS (after aggregation to the same spatial resolution), and remarkable stability with essentially no drift during 2018–2023. Over major anthropogenic source areas, the two OMPS retrievals are generally well-correlated, but N20/OMPS SO2 is biased low, especially for India and the Middle East, where the differences reach ∼ 20 % on average. The reasons for these differences are not fully understood but are partly due to algorithmic differences. Better agreement (typical differences of ∼ 10 %–15 %) is found over degassing volcanoes. SO2 emissions (https://doi.org/10.5067/MEASURES/SO2/DATA406, Fioletov et al., 2022) from large point sources, inferred from N20/OMPS retrievals, agree well with those based on OMI, SNPP/OMPS, and the TROPOspheric Monitoring Instrument (TROPOMI), with correlation coefficients >0.98 and overall differences <10 %. The ratios between the estimated emissions and their uncertainties offer insights into the ability of different satellite instruments to detect and quantify SO2 sources. While TROPOMI has the highest ratios of all four sensors, the ratios from N20/OMPS are slightly greater than OMI and substantially greater than SNPP/OMPS. Overall, our results suggest that the version-1 N20/OMPS SO2 product will successfully continue the long-term OMI and SNPP/OMPS SO2 data records. Efforts currently underway will further enhance the consistency of retrievals between different instruments, facilitating the development of multi-decade, coherent global SO2 datasets across multiple satellites.

Investigating Sulfur Chemistry in the HD163296 Disk

Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood. The protoplanetary disks are the birthplace of planets and its distinctive environment provides an intriguing platform for investigating models of sulfur chemistry. We analyzed the Atacama Large Millimeter/submillimeter Array observations of CS 7–6 transitions in the HD 163296 disk and performed astrochemical modeling to explore its sulfur chemistry. We simulated the distribution of sulfur-containing molecules and compared it with observationally deduced fractional column densities. We have found that the simulated column density of CS is consistent with the observationally deduced fractional column densities, while the simulated column density of C2S is lower than the observationally deduced upper limits on column densities. This results indicate that we have a good understanding of the chemical properties of CS and C2S in the disk. We also investigated the influence of the C/O ratio on sulfur-containing molecules and found that the column densities of SO, SO2, and H2S near the central star are dependent on the C/O ratio. Additionally, we found that the N[CS]/N[SO] ratio can serve as a promising indicator of the disk’s C/O ratio in HD 163296. Overall, the disk of HD 163296 provides a favorable environment for the detection of sulfur-containing molecules.

Tracing sulphur dioxide in volcanic deposits and ash emission during the 2019 Sinabung eruptions

Sulphur dioxide (SO2) emissions from Mt. Sinabung eruption were quantified in time series for 2019. Both pyroclastic materials and gas or aerosol ejected during volcanic eruption contain sulphur as sulphate salt deposits coating volcanic ash grains or gasses. Sulphur dioxide from the eruption will directly impact the surrounding area. Spectral from satellite optical sensors can be used to monitor and measure SO2 gas near real-time after an eruption. The distribution of SO2 column density in the atmosphere was tracked using the Sentinel-5P satellite. Regression kriging (RK) is applied to predict the spatial distribution of sulphur. The area under study is located in a radius of 3 to 7 km from the eruptive center, covering an area of about 4,517 ha. A total of 51 soil samples and volcanic ash were collected from 0- 20 cm soil depth based on a 1x1 km grid interval. All samples were air- dried, sieved, and analyzed for pH, sulphate, and total SO3 using XRF. The Google Earth Engine (GEE) platform was also used to process Sentinel-5P satellite imagery to determine the number and distribution of SO2 column density in the atmosphere during 2019. The pH of the ash is very acidic to neutral (3.56 - 6.55), while soils are considered acidic to neutral (4.67 - 6.52). The available sulphate content in soil ranges from 0 to 303.39 ppm and 0 to 142.47 ppm in volcanic ash samples. SO2 content in ash ranges from 0 to 16.53% and 0 to 3.71% in soils. Sentinel-5P satellite image spectral data shows that SO2 is concentrated mainly in the southern region, with the highest level occurring in August 2019. This study can serve as one of the volcanic mitigation programs and forecast the distribution of SO2 in an active volcanic region of Indonesia.

Spectral Calibration for SO2 Cameras with Light Dilution Effect Correction

The detection ability of SO2 cameras has been improved effectively, while the calibration is still the main factor that limits their measurement accuracy. This paper presents a nonlinear calibration theory by considering the effect of light dilution due to the path radiance as well as the dependence of plume aerosol on scattering wavelength. This new spectral calibration method is used to retrieve the SO2 column density and emission rate of the Etna volcano. Results show that, compared with the DOAS calibration approach, the inversion error can be reduced by 13% if the new spectral calibration is adopted. The superiority of the proposed method will become more obvious for long-distance detection of optically thick plumes.

An algorithm for correction of atmospheric scattering dilution effects in volcanic gas emission measurements using skylight differential optical absorption spectroscopy

Differential Optical Absorption Spectroscopy (DOAS) is commonly used to measure gas emissions from volcanoes. DOAS instruments measure the absorption of solar ultraviolet (UV) radiation scattered in the atmosphere by sulfur dioxide (SO2) and other trace gases contained in volcanic plumes. The standard spectral retrieval methods assume that all measured light comes from behind the plume and has passed through the plume along a straight line. However, a fraction of the light that reaches the instrument may have been scattered beneath the plume and thus has passed around it. Since this component does not contain the absorption signatures of gases in the plume, it effectively “dilutes” the measurements and causes underestimation of the gas abundance in the plume. This dilution effect is small for clean-air conditions and short distances between instrument and plume. However, plume measurements made at long distance and/or in conditions with significant atmospheric aerosol, haze, or clouds may be severely affected. Thus, light dilution is regarded as a major error source in DOAS measurements of volcanic degassing. Several attempts have been made to model the phenomena and the physical mechanisms are today relatively well understood. However, these models require knowledge of the local atmospheric aerosol composition and distribution, parameters that are almost always unknown. Thus, a practical algorithm to quantitatively correct for the dilution effect is still lacking. Here, we propose such an algorithm focused specifically on SO2 measurements. The method relies on the fact that light absorption becomes non-linear for high SO2 loads, and that strong and weak SO2 absorption bands are unequally affected by the diluting signal. These differences can be used to identify when dilution is occurring. Moreover, if we assume that the spectral radiance of the diluting light is identical to the spectrum of light measured away from the plume, a measured clean air spectrum can be used to represent the dilution component. A correction can then be implemented by iteratively subtracting fractions of this clean air spectrum from the measured spectrum until the respective absorption signals on strong and weak SO2 absorption bands are consistent with a single overhead SO2 abundance. In this manner, we can quantify the magnitude of light dilution in each individual measurement spectrum as well as obtaining a dilution-corrected value for the SO2 column density along the line of sight of the instrument. This paper first presents the theory behind the method, then discusses validation experiments using a radiative transfer model, as well as applications to field data obtained under different measurement conditions at three different locations; Fagradalsfjall located on the Reykjanaes peninsula in south Island, Manam located off the northeast coast of mainland Papua New Guinea and Holuhraun located in the inland of north east Island.

Weak degassing from remote Alaska volcanoes characterized with a new airborne imaging DOAS instrument and a suite of in situ sensors

Gas emissions from volcanoes occur when volatile species exsolve from magmatic and hydrothermal systems and make their way to the surface. Measurements of emitted gases therefore provide insights into volcanic processes. On 16 July 2021, we made airborne measurements of weak gas plumes emitted from four remote Alaska volcanoes: Iliamna Volcano, Mount Douglas, Mount Martin, and Mount Mageik. Integrated into a small fixed-wing aircraft, a new Imaging Differential Optical Absorption Spectroscopy (DOAS) instrument was used to map the spatial extent of SO2 plumes as they drifted downwind. Contrary to conventional Mobile DOAS instruments, which provide only a single viewing direction, the Imaging DOAS simultaneously measures SO2 column density along 48 individual viewing directions oriented in a swath above or below the aircraft. Each of the individual measurements have a comparable precision and sensitivity to those obtained by conventional instruments. Together, they provide high resolution 2D imagery of the volcanic plumes and allow calculation of limited emission rate time series information. Although zenith-facing DOAS measurements achieve greater accuracy and are performed here, the application of the Imaging DOAS in a nadir-facing setup is also discussed and compared to satellite observations made in similar geometries. Also onboard the aircraft, a suite of electrochemical and optical sensors measured the relative abundances of the six major volcanic volatile species H2O, CO2, SO2, H2S, HCl, and HF as the aircraft passed through the plumes. Mean SO2 emission rates of 90 ± 10, 20 ± 3, and 13 ± 3 t/d were measured at Iliamna Volcano, Mount Douglas, and Mount Martin, respectively. SO2 emissions were below the DOAS detection limit at Mount Mageik but CO2 and H2S could be measured with the in situ sensors. The information gleaned from these measurements was used to assess and compare activity at these volcanoes, all of which were found to be in a state of background degassing but whose emissions pointed to different source conditions ranging from mixed magmatic-hydrothermal to purely hydrothermal in character. Additional measurements at Mount Spurr, Redoubt Volcano, and Augustine Volcano failed to detect the very weak gas concentrations downwind of these persistently degassing vents.

Ground-Based MAX-DOAS Observation of Trace Gases from 2019 to 2021 in Huaibei, China

With the spread of the COVID-19 pandemic and the implementation of closure measures in 2020, population mobility and human activities have decreased, which has seriously impacted atmospheric quality. Huaibei City is an important coal and chemical production base in East China, which faces increasing environmental problems. The impact of anthropogenic activities on air quality in this area was investigated by comparing the COVID-19 lockdown in 2020 with the normal situation in 2021. Tropospheric NO2, HCHO and SO2 column densities were observed by ground-based multiple axis differential optical absorption spectroscopy (MAX-DOAS). In situ measurements for PM2.5, NO2, SO2 and O3 were also taken. The observation period was divided into four phases, the pre-lockdown period, phase 1 lockdown, phase 2 lockdown and the post-lockdown period. Ground-based MAX-DOAS results showed that tropospheric NO2, HCHO and SO2 column densities increased by 41, 14 and 14%, respectively, during phase 1 in 2021 vs. 2020. In situ results showed that NO2 and SO2 increased by 59 and 11%, respectively, during phase 1 in 2021 vs. 2020, but PM2.5 and O3 decreased by 15 and 17%, respectively. In the phase 2 period, due to the partial lifting of control measures, the concentration of pollutants did not significantly change. The weekly MAX-DOAS results showed that there was no obvious weekend effect of pollutants in the Huaibei area, and NO2, HCHO and SO2 had obvious diurnal variation characteristics. In addition, the relationship between the column densities and wind speed and direction in 2020 and 2021 was studied. The results showed that, in the absence of traffic control in 2021, elevated sources in the Eastern part of the city emitted large amounts of NO2. The observed ratios of HCHO to NO2 suggested that tropospheric ozone production involved NOX-limited scenarios. The correlation analysis between HCHO and different gases showed that HCHO mainly originated from primary emission sources related to SO2.

Physical properties of accretion shocks toward the Class I protostellar system Oph-IRS 44

Context. The final outcome and chemical composition of a planetary system depend on its formation history: the physical processes that were involved and the molecular species available at different stages. Physical processes such as accretion shocks are thought to be common in the protostellar phase, where the envelope component is still present, and they can release molecules from the dust to the gas phase, altering the original chemical composition of the disk. Consequently, the study of accretion shocks is essential for a better understanding of the physical processes at disk scales and their chemical output. Aims. The purpose of this work is to assess how the material from the infalling envelope feeds the disk and the chemical consequences thereof, particularly the characteristics of accretion shocks traced by sulfur-related species. Methods. We present high angular resolution observations (0″.1, corresponding to 14 au) with the Atacama Large Millimeter/submillimeter Array (ALMA) of the Class I protostar Oph-IRS 44 (also known as YLW 16A). The continuum emission at 0.87 mm is observed, together with sulfur-related species such as SO, SO2, and 34SO2. The non-local thermodynamic equilibrium (non-LTE) radiative-transfer tool RADEX and the rotational diagram method are employed to assess the physical conditions of the SO2 emitting region. Results. Six lines of SO2, two lines of 34SO2, and one line of SO are detected toward IRS 44. The emission of all the detected lines peaks at ~0″.1 (~14 au) from the continuum peak and we find infalling-rotating motions inside 30 au. However, only redshifted emission is seen between 50 and 30 au. Colder and more quiescent material is seen toward an offset region located at a distance of ~400 au from the protostar, and we do not find evidence of a Keplerian profile in these data. The SO2 emitting region around the protostar is consistent with dense gas (≥108 cm−3), temperatures above 70 K, high SO2 column densities between 0.4 and 1.8 × 1017 cm−2, line widths between 12 and 14 km s−1, and an abundance ratio SO2/SO ≥ 1, suggesting that some physical mechanism is enhancing the gas-phase SO2 abundance. Conclusions. Accretion shocks are the most plausible explanation for the high temperatures, high densities, and velocities found for the SO2 emission. The offset region seems to be part of a localized streamer that is injecting material to the disk-envelope system through a protrusion observed only in redshifted emission and associated with the highest kinetic temperature. When material enters the disk-envelope system, it generates accretion shocks that increase the dust temperature and desorb SO2 molecules from dust grains. High-energy SO2 transitions (Eup ~ 200 K) seem to be the best tracers of accretion shocks that can be followed up by future higher angular resolution ALMA observations and compared to other species to assess their importance in releasing molecules from the dust to the gas phase.

Highlighting the role of earth observation Sentinel5P TROPOMI in monitoring volcanic eruptions: a report on Hunga Tonga, a Submarine Volcano

ABSTRACT The present study utilized earth observation Sentinel5P TROPOMI (TROPOspheric Monitoring Instrument) data for monitoring submarine volcanic activities. The world has seen a sequence of abrupt volcanic eruptions within one-month duration i.e., on 20th December 2021, 13th January 2022 and 15th January 2022. This caused the emissions of natural gaseous pollutants such as Sulphur Dioxide (SO2), Hydrogen Sulphide (H2S) and ash particles. Atmospheric SO2, AAI (Absorbing Aerosol Index) and Cloud fraction data are retrieved from the TROPOMI onboard the Copernicus Sentinel5P European Space Agency satellite. Results confirmed the increased concentration of SO2 column density after 20th December, and it was observed to be 0.002 mol/m2, the highest concentration during the period of study. Generally, SO2 concentration stays within 0.001 mol/m2 or less. Concentration was seen increasing after the first eruption and reached maximum after 15th January 2022 eruption to a level up to 0.002 mol/m2. Similar outcomes were observed for AAI for the chosen site. AAI values increased to 25,000 fold (AAI values of 1.25) during the first eruption and increased to 29,000 fold on 15th January 2022 after eruptions (AAI values of 1.45) as compared AAI values of 0.005 or negative AAI values before eruptions. A cloud fraction of value 1 is observed during this time, along with the top most cloud height at 14,233.16 m (14.23 kms) above the crater of the volcano (maximum estimation limit by S5P). These values are higher as compared to isolated islands, as there are no other sources of emissions at surrounding environment. The outcomes support the role of Earth Observation datasets for disaster monitoring and management plans for mitigation.

A data-augmentation approach to deriving long-term surface SO2 across Northern China: Implications for interpretable machine learning

Until recently, Northern China was one of the most SO2 polluted regions in the world. The lack of long-term and spatially resolved surface SO2 data hinders retrospective evaluation of relevant environmental policies and human health effects. This study aims to derive the spatiotemporal distribution of surface SO2 across Northern China during 2005–2019. As “concept drift” causes substantial estimation bias in back-extrapolation, we propose a new approach named the robust back-extrapolation via data augmentation approach (RBE-DA) to model the long-term surface SO2. The results show that the population-weighted regional SO2 ([SO2]pw) increased from 2005 to 2007 and decreased steadily afterwards. The [SO2]pw decreased by 80.4% from 74.2 ± 28.4 μg/m3 in 2007 to 14.6 ± 4.8 μg/m3 in 2019. The predicted spatial distributions for each year show that the SO2 pollution was severe (more than 20 μg/m3) in most areas of Northern China until 2017. By using model interpretation methods, we visually reveal the mechanism of estimation bias in the back-extrapolation. Specifically, the training data is severely imbalanced with respect to the satellite-retrieved SO2 column densities (i.e., it is short on high-value samples), so the benchmark model is unable to extrapolate the effects of this important predictor. This study provides long-term surface SO2 data for post hoc evaluation and human exposure assessment in Northern China, while demonstrating that the interpretable machine learning approach is critical for model diagnostics and refinement. Leveraging satellite retrievals, the RBE-DA approach can be applied worldwide to back-extrapolate various measures of air quality.

Absorption spectra measurements at ~1 cm<sup>–1</sup> spectral resolution of <sup>32</sup>S, <sup>33</sup>S, <sup>34</sup>S, and <sup>36</sup>S sulfur dioxide for the 206–220 nm region and applications to modeling of the isotopic self-shielding

The sulfur isotope fractionation that occurs during SO2 photolysis is key to explaining the isotope signatures stored in ancient sedimentary rocks and understanding the atmospheric compositions of the early Earth and early Mars. Here, we report the photoabsorption cross-sections of 32SO2, 33SO2, 34SO2, and 36SO2 measured from 206 to 220 nm at 296 K. The wavelength resolution was set to 1 cm–1, 25 times higher than that of previous SO2 isotopologue absorption spectra measurements. The precision of ~10% is in agreement with previously reported SO2 absorption spectra. In comparison with previously reported high-resolution spectra of natural abundance, SO2 measurements demonstrate smaller cross-sectional magnitudes at absorption peaks and an offset wavelength by ~0.016 nm. Using the newly recorded isotopologue spectra, we calculated the sulfur isotope fractionation for self-shielding during SO2 photolysis. The calculated 34S fractionation (34ε) roughly reproduces the observed relationship between 34ε and the SO2 column density in previous photolysis experiments. Thus, the cross-section is useful for predicting 34S/32S isotope fractionation in an optically thick SO2 atmosphere. In contrast, for mass-independent fractionation (MIF-S, i.e., non-zero Δ33S), the measured spectra predicted a weakly negative Δ33S/δ34S slope of about –0.1. The small Δ33S/δ34S slope is consistent with the slopes of SO2 photolysis experiments under high-pressure atmospheres (i.e., the pressure broadened absorption line width will be comparable to the spectral resolution). Therefore, MIF-S during photolysis experiments was linked to spectroscopic measurements for the first time. We conclude that reasonable precision and high-resolution spectroscopic measurements are key to explaining the origin of MIF-S at column densities below 1018 cm–2. However, MIF-S production in chamber experiments or atmospheric conditions may require understanding pressure or temperature effects, such as linewidth broadening on the UV-absorption spectra, and how these effects manifest themselves on isotopologues.

Day–Night Monitoring of Volcanic SO2 and Ash Clouds for Aviation Avoidance at Northern Polar Latitudes

We describe NASA’s Applied Sciences Disasters Program, which is a collaborative project between the Direct Readout Laboratory (DRL), ozone processing team, Jet Propulsion Laboratory, Geographic Information Network of Alaska (GINA), and Finnish Meteorological Institute (FMI), to expedite the processing and delivery of direct readout (DR) volcanic ash and sulfur dioxide (SO2) satellite data. We developed low-latency quantitative retrievals of SO2 column density from the solar backscattered ultraviolet (UV) measurements using the Ozone Mapping and Profiler Suite (OMPS) spectrometers as well as the thermal infrared (TIR) SO2 and ash indices using Visible Infrared Imaging Radiometer Suite (VIIRS) instruments, all flying aboard US polar-orbiting meteorological satellites. The VIIRS TIR indices were developed to address the critical need for nighttime coverage over northern polar regions. Our UV and TIR SO2 and ash software packages were designed for the DRL’s International Planetary Observation Processing Package (IPOPP); IPOPP runs operationally at GINA and FMI stations in Fairbanks, Alaska, and Sodankylä, Finland. The data are produced within 30 min of satellite overpasses and are distributed to the Alaska Volcano Observatory and Anchorage Volcanic Ash Advisory Center. FMI receives DR data from GINA and posts composite Arctic maps for ozone, volcanic SO2, and UV aerosol index (UVAI, proxy for ash or smoke) on its public website and provides DR data to EUMETCast users. The IPOPP-based software packages are available through DRL to a broad DR user community worldwide.

ALMA Observation of SO2 Gas Originating from Io’s Volcanic Plume and Lava Areas

Abstract We detected the submillimeter spectrum of SO2 gas originating from volcanic plumes and lava areas in Jupiter’s moon Io by analyzing the ALMA archive data observed before and after ingress on 2018 March. As a result of synthesis imaging, high intensity regions of SO2 were found to be associated with the volcanically active areas around the Amaterasu Patera (305°W, 38°N) and around the Janus Patera (36°W, 4°S) and Kanehekili Fluctus (32°W, 17°S). By fitting the spectral lineshapes, the main and redshifted spectral components are identified around the Amaterasu Patera. The redshifted component can be attributed as the emission from the plume gas moving away in the line of sight. The rotational temperature and column density of SO2 were derived by employing the population diagram plots with spectral line intensities. The column densities of SO2 before ingress are (2.2 ± 1.1) × 1015 cm−2 around the Amaterasu Patera and (2.2 ± 1.1) × 1015 cm−2 around the Janus Patera. After ingress, the column densities are (1.8 ± 1.2) × 1015 cm−2 and (2.1 ± 0.1) × 1015 cm−2, respectively. This suggests that volcanic eruptions maintain the atmospheres in these regions during eclipse. The temperature around the Amaterasu Patera of 95 ± 28 K before ingress is similar to the temperature of 108 ± 48 K after ingress. On the other hand, the temperature around the Janus Patera increases from 151 ± 70 K before ingress to 311 ± 41 K after ingress. The result suggests that the atmospheric SO2 around the Janus Patera after ingress may be supplied by evaporation from the lava areas.

A Spectra Classification Methodology of Hyperspectral Infrared Images for Near Real-Time Estimation of the SO2 Emission Flux from Mount Etna with LARA Radiative Transfer Retrieval Model

Fast and accurate quantification of gas fluxes emitted by volcanoes is essential for the risk mitigation of explosive eruption, and for the fundamental understanding of shallow eruptive processes. Sulphur dioxide (SO2), in particular, is a reliable indicator to predict upcoming eruptions, and its systemic characterization allows the rapid assessment of sudden changes in eruptive dynamics. In this regard, infrared (IR) hyperspectral imaging is a promising new technology for accurately measure SO2 fluxes day and night at a frame rate down to 1 image per second. The thermal infrared region is not very sensitive to particle scattering, which is an asset for the study of volcanic plume. A ground based infrared hyperspectral imager was deployed during the IMAGETNA campaign in 2015 and provided high spectral resolution images of the Mount Etna (Sicily, Italy) plume from the North East Crater (NEC), mainly. The LongWave InfraRed (LWIR) hyperspectral imager, hereafter name Hyper-Cam, ranges between 850–1300 cm−1 (7.7–11.8 µm). The LATMOS (Laboratoire Atmosphères Milieux Observations Spatiales) Atmospheric Retrieval Algorithm (LARA), which is used to retrieve the slant column densities (SCD) of SO2, is a robust and a complete radiative transfer model, well adapted to the inversion of ground-based remote measurements. However, the calculation time to process the raw data and retrieve the infrared spectra, which is about seven days for the retrieval of one image of SO2 SCD, remains too high to infer near real-time (NRT) SO2 emission fluxes. A spectral image classification methodology based on two parameters extracting spectral features in the O3 and SO2 emission bands was developed to create a library. The relevance is evaluated in detail through tests. From data acquisition to the generation of SO2 SCD images, this method requires only ~40 s per image, which opens the possibility to infer NRT estimation of SO2 emission fluxes from IR hyperspectral imager measurements.

Io's SO2 atmosphere from HST Lyman-α images: 1997 to 2018

The atmosphere of Jupiter's volcanic moon Io consists of mainly sulfur dioxide (SO2), and this main constituent has been studied with a variety of observing techniques across many wavelengths over the years. Here we study absorption by SO2 at the hydrogen Ly-α line (1216 Å) in a large set of images taken by the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST) between 1997 and 2018. An advanced statistical analysis using a Monte-Carlo trial method is applied to derive the SO2 column density from the Ly-α intensity, which includes the uncertainties of the used variables such as solar and background flux. Our analysis produces a probability distribution function of the SO2 column density and highlights some short-comings of the observing technique. Most importantly, the HST/STIS images of the surface-reflected Ly-α flux are only sensitive to SO2 column densities between ~1015 cm−2 and ~5×1016 cm−2. Due to strong non-linearity in the relationship between the SO2 abundance and the Ly-α flux at the low and high values of detected flux, SO2 abundance directly retrieved from the STIS images will generally fall within these boundaries. This explains the relatively low equatorial column density of about 1016 cm−2 reported by previous studies using the Ly-α images (e.g., Feldman et al., 2000; Feaga et al., 2009) compared to other studies (e.g., Spencer et al., 2005; Tsang et al., 2013; Jessup and Spencer, 2015; Lellouch et al., 2015), where the obtained column density is often 1017 cm−2. By assuming a log-normal probability distribution function for the column density, a new estimate of the SO2 column density is then fitted, indirectly accounting for abundances beyond the detectability limits. This method suggests slightly higher equatorial SO2 abundances and much larger upper-limits, revealing that the Ly-α observations are in fact consistent with the higher abundances found in other studies. We then investigate the SO2 abundances at three volcanic sites (Loki, Marduk, Thor), where plumes were observed before and where the sensitivity in our images is comparably high. The observations did not reveal transient changes due to local outgassing at any of the three sites. Finally, the heliocentric distance of Io changed from 4.95 AU to 5.45 AU between the observation dates, potentially allowing us to investigate the influence of solar intensity changes on the SO2 column density via surface frost sublimation. However, the derived error bars are significantly larger than the derived variability, preventing any firm conclusion on seasonal changes and local volcanic outgassing.

First Measurements of Gas Flux with a Low-Cost Smartphone Sensor-Based UV Camera on the Volcanoes of Northern Chile

UV cameras have been used for over a decade in order to remotely sense SO2 emission rates from active volcanoes, and to thereby enhance our understanding of processes related to active and passive degassing. Whilst SO2 column density retrievals can be more accurate/sophisticated using alternative techniques (e.g., Differential Optical Absorption Spectrometer (DOAS), Correlation Spectrometer (COSPEC)), due to their higher spectral resolutions, UV cameras provide the advantage of high time-resolution emission rates, a much greater spatial resolution, and the ability to simultaneously retrieve plume speeds. Nevertheless, the relatively high costs have limited their uptake to a limited number of research groups and volcanic observatories across the planet. One recent intervention in this regard has been the introduction of the PiCam UV camera, which has considerably lowered instrumental cost. Here we present the first data obtained with the PiCam system from seven persistently degassing volcanoes in northern Chile, demonstrating robust field operation in challenging conditions and over an extended period of time, hence adding credence to the potential of these units for more widespread dissemination to the international volcanic gas measurement community. Small and weak plumes, as well as strongly degassing plumes were measured at distances ranging 0.6–10.8 km from the sources, resulting in a wide range of SO2 emission rates, varying from 3.8 ± 1.8 to 361 ± 31.6 td−1. Our acquired data are discussed with reference to previously reported emission rates from other ground-based remotely sensed techniques at the same volcanoes, in particular considering: resolution of single plume emissions in multi-plume volcanoes, light dilution, plume geometry, seasonal effects, and the applied plume speed measurement methodology. The main internal/external factors that influence positive/negative PiCam measurements include camera shake, light dilution, and the performance of the OpenCV and control points post processing methods. A simple reprocessing method is presented in order to correct the camera shake. Finally, volcanoes were separated into two distinct groups: low and moderate SO2 emission rates systems. These groups correlate positively with their volcanological characteristics, especially with the fluid compositions from fumaroles.

An attempt to detect transient changes in Io’s SO[formula omitted] and NaCl atmosphere

Io’s atmosphere is predominately SO2 that is sustained by a combination of volcanic outgassing and sublimation. The loss from the atmosphere is the main mass source for Jupiter’s large magnetosphere. Numerous previous studies attributed various transient phenomena in Io’s environment and Jupiter’s magnetosphere to a sudden change in the mass loss from the atmosphere supposedly triggered by a change in volcanic activity. Since the gas in volcanic plumes does not escape directly, such causal correlation would require a transient volcano-induced change in atmospheric abundance, which has never been observed so far.Here we report four observations of atmospheric SO2 and NaCl from the same hemisphere of Io, obtained with the IRAM NOEMA interferometer on 11 December 2016, 14 March, 6 and 29 April 2017. These observations are compared to measurements of volcanic hot spots and Io’s neutral and plasma environment. We find a stable NaCl column density in Io’s atmosphere on the four dates. The SO2 column density derived for December 2016 is about 30% lower compared to the SO2 column density found in the period of March to April 2017. This increase in SO2 from December 2016 to March 2017 might be related to increasing volcanic activity observed at several sites in spring 2017, but the stability of the volcanic trace gas NaCl and resulting decrease in NaCl/SO2 ratio do not support this interpretation. Observed dimmings in both the sulfur ion torus and Na neutral cloud suggest rather a decrease in mass loading in the period of increasing SO2 abundance. The dimming Na brightness and stable atmospheric NaCl furthermore dispute an earlier suggested positive correlation of the sodium cloud and the hot spot activity at Loki Patara, which considerably increased in this period. The environment of Io overall appears to be in a rather quiescent state, preventing further conclusions. Only Jupiter’s aurora morphology underwent several short-term changes, which are apparently unrelated to Io’s quiescent environment or the relatively stable atmosphere.

Air quality impacts of the 2018 Mt. Kilauea Volcano eruption in Hawaii: A regional chemical transport model study with satellite-constrained emissions

Abstract Volcanic eruptions could bring a vast amount of sulfur dioxide (SO2) and ash into the air, often imposing substantial impacts on air quality and the ecosystem. Quantifying its impacts, however, is difficult due to the uncertainties in estimating the strength and variations of volcanic emissions. Here we developed and evaluated a new approach to combine satellite SO2 detection and chemical transport modeling to assess the impact of the 2018 Mt. Kilauea eruption on air quality over Hawaii. During the sustained eruption of the Kilauea Volcano in Hawaii's Big Island from May to July 2018, considerable SO2 and PM2.5 enhancements were observed both from the ground and from space. We studied this case using an experimental version of the NOAA National Air Quality Forecast Capability (NAQFC) modeling system. Daily emissions of SO2 and ash were estimated using a combination of SO2 column density retrieved by Ozone Mapping and Profiling Suite (OMPS) Nadir-Mapper (NM) aboard the Suomi-NPP satellite and the NAQFC model with an inverse emission modeling approach. We found that the volcanic SO2 emission rates peaked at 15,000 mol/s from the Kilauea's East Rift zone and Summit. The formation and transport of volcanic smog, or Vog, was highly dependent upon the vertical distribution of the volcanic emission, controlled by the heat flux of emission sources. We conducted four model simulations with various emission settings, and compared them to satellite data (CALIOP, OMPS and VIIRS) and in-situ measurements. All the runs tended to underpredict the peak values of surface SO2 and PM2.5 (particulate matter smaller than 2.5 μm in diameter). The “No Plume Rise” run underestimated the Vog plume rise and downstream transport. Using fixed emission rate or removing the temporal variations (”3-Day Mean”) led to miss peak Vog effects or inconsistent transport pattern compared to the observations. Therefore, the Base simulation with daily-varying emission and plume rise was used to quantify the air quality effects of the Kilauea eruption. We found that the volcanic eruption elevated surface PM2.5 concentration by 30–40 μg/m3 in the southeast part of the Big Island, with peak values up to 300 μg/m3. The Vog effect on trace gases, such as O3, NOx, and non-methane hydrocarbons, were much weaker (

SO2 Emission Estimates Using OMI SO2 Retrievals for 2005-2017.

SO2 column densities from Ozone Monitoring Instrument provide important information on emission trends and missing sources, but there are discrepancies between different retrieval products. We employ three Ozone Monitoring Instrument SO2 retrieval products (National Aeronautics and Space Administration (NASA) standard (SP), NASA prototype, and BIRA) to study the magnitude and trend of SO2 emissions. SO2 column densities from these retrievals are most consistent when viewing angles and solar zenith angles are small, suggesting more robust emission estimates in summer and at low latitudes. We then apply a hybrid 4D‐Var/mass balance emission inversion to derive monthly SO2 emissions from the NASA SP and BIRA products. Compared to HTAPv2 emissions in 2010, both posterior emission estimates are lower in United States, India, and Southeast China, but show different changes of emissions in North China Plain. The discrepancies between monthly NASA and BIRA posterior emissions in 2010 are less than or equal to 17% in China and 34% in India. SO2 emissions increase from 2005 to 2016 by 35% (NASA)–48% (BIRA) in India, but decrease in China by 23% (NASA)–33% (BIRA) since 2008. Compared to in situ measurements, the posterior GEOS‐Chem surface SO2 concentrations have reduced NMB in China, the United States, and India but not in South Korea in 2010. BIRA posteriors have better consistency with the annual growth rate of surface SO2 measurement in China and spatial variability of SO2 concentration in China, South Korea, and India, whereas NASA SP posteriors have better seasonality. These evaluations demonstrate the capability to recover SO2 emissions using Ozone Monitoring Instrument observations.

Extended database of SO2 column densities over Pakistan by exploiting satellite observations

Increasing levels of atmospheric SO2 is a major threat and is now widely included in health risk assessment studies. An annual estimation of SO2 has been conducted for both anthropogenic and natural activities at country level. Satellite observations of atmospheric sulfur dioxide (SO2) are obtained over Pakistan during the time span of 2005–2016. The data was acquired from the Ozone Monitoring Instrument (OMI) onboard NASA's Aura satellite. DOAS (Differential Optical Absorption Spectroscopy) based algorithm was utilized to retrieve SO2 column densities. In addition to spatio-temporal analysis of SO2 column, seasonal cycles over major areas of Pakistan are evaluated and discussed. Year 2007, 2011 exhibited anomalous high levels of SO2 attributed to trans-boundary volcanic plumes observed in Pakistan. SO2 plumes were caused by Dallafilla and Nabro volcanic eruption and spread over East African, the Middle Eastern and South Asian regions. A temporal increase of about 78% was observed in anthropogenic SO2 levels for a period of 2005–2016 across Pakistan. Further, the relative change was maximum in Khyber Pakhtoon Khwa (KPK region 46%) followed by Punjab (38%), Sindh (28%) and Baluchistan (18%), respectively. The economic prosperity in recent years resulted in increased demand for energy by both the industrial and domestic sector, and consequent increase in SO2 emissions in Pakistan.