Emission of volatile halogenated organic compounds over various landforms at the Dead Sea

Abstract. Volatile halogenated organic compounds (VHOCs), such as methyl halides (CH3X; X = Br, Cl and I) and very short-lived halogenated substances (VSLS; CHBr3, CH2Br2, CHBrCl2, C2HCl3, CHCl3 and CHBr2Cl) are well known for their significant influence on ozone concentrations and oxidation capacity of the troposphere and stratosphere, and for their key role in aerosol formation. Insufficient characterization of the sources and emission rate of VHOCs limits our present ability to understand and assess their impact in both the troposphere and the stratosphere. Over the last two decades several natural terrestrial sources for VHOCs, including soil and vegetation, have been identified, but our knowledge about emission rates from these sources and their responses to changes in ambient conditions remains limited. Here we report measurements of the mixing ratios and the fluxes of several chlorinated and brominated VHOCs from different landforms and vegetated sites at the Dead Sea during different seasons. Fluxes were highly variable but were generally positive (emissive), corresponding with elevated mixing ratios for all of the VHOCs investigated in the four investigated site types – bare soil, coastal, cultivated and natural vegetated sites – except for fluxes of CH3I and C2HCl3 over the vegetated sites. In contrast to previous reports, we also observed emissions of brominated trihalomethanes, with net molar fluxes ordered as follows: CHBr2Cl > CHBr3 > CHBrCl2 > CHCl3. This finding can be explained by the enrichment of soil with Br. Correlation analysis, in agreement with recent studies, indicated common controls for the formation and emission of all the above trihalomethanes but also for CH2Br2. Also in line with previous reports, we observed elevated emissions of CHCl3 and C2HCl3 from mixtures of soil and different salt-deposited structures; the high correlations of flux with methyl halides, and particularly with CH3I, suggested that at least CH3I is also emitted via similar mechanisms or is subjected to similar controls. Overall, our results indicate elevate emission of VHOCs from bare soil under semi-arid conditions. Along with other recent studies, our findings point to the strong emission potential of a suite of VHOCs from saline soils and salt lakes, and call for additional studies of emission rates and mechanisms of VHOCs from saline soils and salt lakes

An Experimental Approach to a Rapid Propulsion and Aeronautics Concepts Testbed

Modern aircraft design tools have limitations for predicting complex propulsion-airframe interactions. The demand for new tools and methods addressing these limitations is high based on the many recent Distributed Electric Propulsion (DEP) Vertical Take-Off and Landing (VTOL) concepts being developed for Urban Air Mobility (UAM) markets. We propose that low cost electronics and additive manufacturing can support the conceptual design of advanced autonomy-enabled concepts, by facilitating rapid prototyping for experimentally driven design cycles. This approach has the potential to reduce complex aircraft concept development costs, minimize unique risks associated with the conceptual design, and shorten development schedule by enabling the determination of many "unknown unknowns" earlier in the design process and providing verification of the results from aircraft design tools. A modular testbed was designed and built to evaluate this rapid design-build-test approach and to support aeronautics and autonomy research targeting UAM applications utilizing a complex, transitioning-VTOL aircraft configuration. The testbed is a modular wind tunnel and flight model. The testbed airframe is approximately 80% printed, with labor required for assembly. This paper describes the design process, fabrication process, ground testing, and initial wind tunnel structural and thermal loading of a proof-of-concept aircraft, the Langley Aerodrome 8 (LA-8)

Greased Lightning (GL-10) Performance Flight Research: Flight Data Report

Modern aircraft design methods have produced acceptable designs for large conventional aircraft performance. With revolutionary electronic propulsion technologies fueled by the growth in the small UAS (Unmanned Aerial Systems) industry, these same prediction models are being applied to new smaller, and experimental design concepts requiring a VTOL (Vertical Take Off and Landing) capability for ODM (On Demand Mobility). A 50% sub-scale GL-10 flight model was built and tested to demonstrate the transition from hover to forward flight utilizing DEP (Distributed Electric Propulsion)[1][2]. In 2016 plans were put in place to conduct performance flight testing on the 50% sub-scale GL-10 flight model to support a NASA project called DELIVER (Design Environment for Novel Vertical Lift Vehicles). DELIVER was investigating the feasibility of including smaller and more experimental aircraft configurations into a NASA design tool called NDARC (NASA Design and Analysis of Rotorcraft)[3]. This report covers the performance flight data collected during flight testing of the GL-10 50% sub-scale flight model conducted at Beaver Dam Airpark, VA. Overall the flight test data provides great insight into how well our existing conceptual design tools predict the performance of small scale experimental DEP concepts. Low fidelity conceptual design tools estimated the (L/D)( sub max)of the GL-10 50% sub-scale flight model to be 16. Experimentally measured (L/D)( sub max) for the GL-10 50% scale flight model was 7.2. The aerodynamic performance predicted versus measured highlights the complexity of wing and nacelle interactions which is not currently accounted for in existing low fidelity tools

Copper Catalyzed Oceanic Methyl Halide Production

Methyl halides are found in all of Earth’s biomes, produced naturally or through manmade means. Their presence in the atmosphere is problematic, as they catalyze depletion of stratospheric ozone. To understand the full environmental impact of these compounds, it is important to identify their chemical cycling processes. Iron increases methyl halide production in soils and oceans, yet copper’s influence remains unknown despite its similar chemical oxidation properties to iron. I experimentally tested the effect of copper sulfate and sunlight on methyl halide fluxes in San Francisco Bay seawater. Samples exposed to copper sulfate and sunlight averaged higher positive flux rates than other treatments. Copper sulfate also increased carbon dioxide production and acidification of the water. The interaction of copper sulfate and sunlight in seawater suggests a new mechanism for methyl halide production, most likely via a photochemical reaction or through suppression of normal uptake processes causing overabundant concentrations

Methyl halide and methane fluxes in the northern Alaskan coastal tundra

[ 1] The Arctic tundra is a major source and sink of carbon-containing gases, but the biogeochemical cycling of halocarbons in this ecosystem has been largely unexplored. In this study, coastal tundra fluxes of methyl halides (CH3Cl, CH3Br, and CH3I) and methane (CH4) were measured near Barrow, Alaska (71 degrees N, 157 degrees W) during the 2005 growing season. Sites covered a range of microtopographic features including drained lake basins, channels, and high- and low-centered ice-wedge polygons. CH3Cl and CH3Br fluxes varied significantly with hydrologic conditions, with progressively higher net uptake rates observed with decreasing soil saturation. Drained tundra sites averaged - 620 nmol CH3Cl m(-2) d(-1) and - 9.8 nmol CH3Br m(-2) d(-1) while flooded tundra sites averaged -14 nmol CH3Cl m(-2) d(-1) and + 1.1 nmol CH3Br m(-2) d(-1). CH3Cl and CH3Br fluxes were positively correlated with each other as well as with CH4 emissions, suggesting that consumption of both compounds occurs primarily in aerobic environments. Average CH3I net emissions were relatively weak (4.0 nmol m(-2) d(-1)). Average methane fluxes (2.0 mmol m(-2) d(-1)) and their relationship with soil moisture were comparable to tundra emissions reported by prior studies. Methane fluxes showed a marked seasonality, with emissions tripling between early and late in the growing season, but methyl halide fluxes did not show a similar temporal trend. If these measurements are representative of the Arctic tundra, then the Arctic tundra is a regionally important sink for CH3Cl and CH3Br but a trivial source of CH3I.</p