Earth Observation Data Group

Abstract:

Abstract Benzene is a simple neutral aromatic compound found in molecular clouds, comets, and planetary atmospheres. It has been confirmed on Jupiter, Saturn, Titan, and is expected on exoplanets. In this paper, the decomposition of benzene in a simulated asteroid or comet impact into an N2-dominated atmosphere was investigated. The impact plasma was simulated with laser-induced dielectric breakdown and the gas phase decomposition products were observed using high-resolution Fourier transform infrared spectroscopy. The gas phase decomposition products involve mainly HCN, C2H2, and smaller amounts of CH4 with yields of 3.1%–24.0%, 0–11.7%, and 0.5%–3.3%, respectively. Furthermore, in presence of water, benzene also produces CO and CO2 with yields of 2.4%–35.1% and 0.01%–4.8%, respectively. The oxidation state of the product mixture is proportional to the water content. Apart from that, a black-brownish solid phase is formed during the experiments, which makes up about 60% of the original carbon content. Our results therefore show that in anoxic N2-dominated planetary atmospheres, impacts might lead to the depletion of benzene and the formation of HCN, C2H2, and CH4 and, in the presence of water, to the formation of CO and CO2.

Abstract:

Field-portable Open Path Fourier Transform Infrared (OP-FTIR) spectrometers can be used to remotely measure the composition of volcanic plumes using absorption spectroscopy, providing invaluable data on total gas emissions. Quantifying the temporal evolution of gas compositions during an eruption helps develop models of volcanic processes and aids in eruption forecasting. Absorption measurements require a viewing geometry which aligns infrared source, plume, and instrument, which can be challenging. Here, we present a fast retrieval algorithm to estimate quantities of gas, ash and sulphate aerosols from thermal emission OP-FTIR measurements, and the results from two pilot campaigns on Stromboli volcano in Italy in 2019 and 2021. We validate the method by comparing time series of SO2 slant column densities retrieved using our method with those obtained from a conventional UV spectrometer, demonstrating that the two methods generally agree to within a factor of 2. The algorithm correctly identifies ash-rich plumes and gas bursts associated with explosions and quantifies the mass column densities and particle sizes of ash and sulphate aerosols (SA) in the plume. We compare the ash sizes retrieved using our method with the particle size distribution (PSD) of an ash sample collected during the period of measurements in 2019 by flying a Remotely Piloted Aircraft System into the path of a drifting ash plume and find that both modes of the bimodal PSD (a fine fraction with diameter around 5–10 μm and a coarse fraction around 65 μm) are identified within our datasets at different times. We measure a decrease in the retrieved ash particle size with distance downwind, consistent with settling of larger particles, which we also observed visually. We measure a decrease in the SO2/SA ratio as the plume travels downwind, coupled with an increase in measured SA particle size (range 2–6 μm), suggesting rapid hygroscopic particle growth and/or SO2 oxidation. We propose that infrared emission spectroscopy can be used to examine physical and chemical changes during plume transport and opens the possibility of remote night-time monitoring of volcanic plume emissions. These ground-based analyses may also aid the refinement of satellite-based aerosol retrievals.

Abstract:

A series of explosive eruptions began at La Soufrière, on St Vincent, on 9th April 2021, with the last event occurring on 22nd April. The eruption was observed by the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite East (GOES-East) platform. The instrument measures in 16 channels in the visible, near-infrared and infrared, across a large area which includes the Carribean. During the La Soufrière eruption, the ABI instrument made measurements for the full disc every 10-minutes, and for part of the eruption, a mesoscale region was moved over the volcano, providing data every minute. In this study, data from this satellite instrument has been used to construct four images: (a) a true colour image, (b) a false colour image (12.3 - 10.3 µm, 11.2 - 8.4 µm and 10.3 µm channels assigned to red, green and blue respectively), (c) 10.3 - 11.2 µm brightness temperature difference, and (d) 11.2 - 12.3 µm brightness temperature difference. These have been used to study the plumes produced during the April 2021 eruption, allowing the identification of at least 35 explosive events. In this repository, an animation of the created images has been provided for each of the explosive events identified. The animation names are constructed to indicate the volcano (LaSoufriere), the instrument (ABI), the type of data (i.e. full disc or meso), the event number, the start date/time (yyyymmddhhmm) and the end date/time (yyyymmddhhmm). For example: ‘LaSoufriere_ABI_full_event01_202104091250_202104091740.mp4’ Note that the start and end times indicate the start time of measurement period and some adjustment is needed to ascertain the time over the volcano for the full disc (~ +243 seconds). This has been accounted for in the title shown in each frame of the full disc animations. Also note that two animations are provided for event 5 as measurements from the mesoscale region began during this period. We are grateful to the NOAA Big Data Program through which the GOES-16 data are available. These animations accompany a paper: Taylor, I.A., Grainger, R.G., Prata, A.T., Proud, S,R, Mather, T.A., Pyle, D.M.: A satellite chronology of plumes from the April 2021 eruption of La Soufrière, St Vincent, Accepted for publication in Atmospheric, Chemistry and Physics.

Abstract:

Unsieved ash density measurements from 23 unsieved raw ash samples originating from 15 volcanoes, including mass of sample measured with a digital scale and volume measured with a nitrogen gas pycnometer. Data measured in July-August 2022.