Earth Observation Data Group

Abstract:

Uncertainty-bounded satellite retrievals of volcanic ash cloud properties such as ash cloud-top height, effective radius, optical depth and mass loading are needed for the robust quantitative assessment required to warn aviation of potential hazards. Moreover, there is an imperative to improve quantitative ash cloud estimation due to the planned move towards quantitative ash concentration forecasts by the Volcanic Ash Advisory Centers. Here we apply the Optimal Retrieval of Aerosol and Cloud (ORAC) algorithm to Advanced Himawari Imager (AHI) measurements of the ash clouds produced by the June 2019 Raikoke (Russia) eruption. The ORAC algorithm uses an optimal estimation technique to consolidate a priori information, satellite measurements and associated uncertainties into uncertainty-bounded estimates of the desired state variables. Using ORAC, we demonstrate several improvements in thermal infrared volcanic ash retrievals applied to broadband imagers. These include an improved treatment of measurement noise, accounting for multi-layer cloud scenarios, distinguishing between heights in the troposphere and stratosphere, and the retrieval of a wider range of effective radii sizes than existing techniques by exploiting information from the 10.4 µm channel. Our results indicate that 0.73 ± 0.40 Tg of very fine ash (radius ≤ 15 µm) was injected into the atmosphere during the main eruptive period from 21 June 18:00 UTC to 22 June 10:00 UTC. The total mass of very fine ash decreased from 0.73 to 0.10 Tg over ∼ 48 h, with an e-folding time of 20 h. We estimate a distal fine ash mass fraction of 0.73 % ± 0.62 % based on the total mass of very fine ash retrieved and the ORAC-derived height–time series. Several distinct ash layers were revealed by the ORAC height retrievals. Generally, ash in the troposphere was composed of larger particles than ash present in the stratosphere. We also find that median ash cloud concentrations fall below peak ash concentration safety limits (< 4 mg m−3) 11–16 h after the eruption begins, if typical ash cloud geometric thicknesses are assumed. The ORAC height retrievals for the near-source plume showed good agreement with GOES-17 side-view height data (R=0.84; bias = −0.75 km); however, a larger negative bias was found when comparing ORAC height retrievals for distal ash clouds against Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP) measurements (R=0.67; bias = −2.67 km). The dataset generated here provides uncertainties at the pixel level for all retrieved variables and could potentially be used for dispersion model validation or be implemented in data assimilation schemes. Future work should focus on improving ash detection, improving height estimation in the stratosphere and exploring the added benefit of visible channels for retrieving effective radius and optical depth in opaque regions of nascent ash plumes.

Abstract:

&lt;div&gt;Asteroids and comets are often rich in polyaromatic hydrocarbons (PAHs), which represent in general about 30 % of total carbon in space. The fate of these molecules in extraterrestrial delivery was investigated by experimentally simulating asteroid impacts &amp;#8211; using laser induced breakdown (LIBD) &amp;#8211; into rocky planetary atmospheres and surfaces. Experiments were performed with benzene, naphtalene and anthracene as simple members of PAHs. The effect of LIBD on chemistry of these compounds in various chemical environments, such as atmospheric composition and solid phase matrices, were also studied. The main gas phase products are acetylene and HCN, followed by CO and CO2, whose yields mainly depend on the content of water vapour in the atmosphere. A brownish solid product was also observed. Therefore, simple aromatic compounds, and likely also PAHs, can be a viable source of HCN &amp;#8211; molecule with significant prebiotic importance&amp;#8211; in planetary environments.&lt;/div&gt; &lt;div&gt;&amp;#160;&lt;/div&gt;

Abstract:

&lt;p&gt;Several of the Venera, Vega and Pioneer probe data as well as ground based observation support the presence of so-called Redox Disequilibrium Pairs (RDPs) in atmosphere of so hostile world as Venus (Greaves 2021). State of the art chemical networks cannot explain origin of an important RDP, phosphine, in oxidized atmosphere of Venus by a conventional processes (Bains 2021). We used the hybrid Density Functional Theory (DFT) for investigation of a series of chemical reaction pathways leading to the reduction of phosphate monoxide to phosphine. Our calculations indicated that a reaction network similar to photochemical synthesis of methane from carbon monoxide over acidic surfaces suggested for Mars (Civi&amp;#353; 2019) can also occur in clouds of Venus. As a seminal step, we have explored &amp;#8211; via state-of-the-art quantum-based calculations &amp;#8211; the a priori energetic feasibility of the following reaction:&lt;/p&gt;&lt;p&gt;HCO(radical) + PO = CO2 + PH (biradical).&lt;/p&gt;&lt;p&gt;Our calculations have shown that chemical conversion is constituted of three steps. Two of them are energetically favoured, however, the final conversion to phosphine is hardened by a significant activation barrier. This barrier can be overcome by a reaction of OPH radical with hydrogen radical. For assessing the potential of the newly introduced reaction mechanisms, models of the Venus and early Earth atmospheres in ARGO code and modified STAND chemical network were created and verified. Comparison of reaction yields suggests that this pathway is potentially effective enough and could be the source of phosphine recently discovered on Venus.&amp;#160;&lt;/p&gt;&lt;p&gt;We acknowledge the support provided by the Czech Science Foundation within the project reg. no. 21-11366S and by ERDF/ESF &quot;Centre of Advanced Applied Sciences&quot; (No. CZ.02.1.01/0.0/0.0/16_019/0000778). We acknowledge support of the Czech Academy of Sciences, Strategy AV21, project VP16. The Czech team is part of the VenSpec-H Consortium onboard the ESA EnVision mission.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Civi&amp;#353; S. et al.: Formation of Methane and (Per)Chlorates on Mars. ACS Earth Space Chem. 2019, 3, 2, 221&amp;#8211;232.&lt;/p&gt;&lt;p&gt;Bains W. et al.: Phosphine on Venus Cannot Be Explained by Conventional Processes. Astrobiology 2021, 10 (21), 1277-1304.&lt;/p&gt;&lt;p&gt;Greaves J. S. et al.: &amp;#160;Phosphine gas in the cloud decks of Venus. Nature Astronomy 2021, 5, 655&amp;#8211;664.&lt;/p&gt;

Abstract:

&lt;p&gt;Benzene is the simplest organic compound with a 6-carbon aromatic ring. As such, it was used as a first order representative of aromatic compounds in planetary atmospheres. These compounds can be brought by asteroid&amp;#160;impacts into rocky planetary atmospheres, where they can serve as precursors for further synthesis. Our experiments show that benzene vapours in nitrogen-dominated atmospheres subjected to asteroid&amp;#160;impacts (modelled by laboratory laser shots) lead&amp;#160;to the formation of acetylene and hydrogen cyanide. Both these products appear in many proposed mechanisms of prebiotic chemistry.&lt;/p&gt;