Range Of Mixing Ratios Research Articles

MAX-DOAS measurements and vertical profiles of glyoxal and formaldehyde in Madrid, Spain

Glyoxal (CHOCHO) and formaldehyde (HCHO) are organic trace gases that play an important role in tropospheric chemistry as oxidation products of a number of volatile organic compounds (VOCs). In this study, we report year-round daytime measurements of glyoxal and formaldehyde in the urban atmosphere of Madrid, Spain. Their vertical concentration profiles were retrieved using the Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique and a Radiative Transfer Model (RTM) that simulates solar photon paths through the atmosphere. The diurnal variations of HCHO show two distinct peaks during the day, in the early morning and late afternoon in spring and summer, while the second peak is shifted towards noon in autumn and winter, due to lower photolysis rates and more effective boundary layer accumulation of HCHO in those seasons. The HCHO surface mixing ratios range from 6 ppbv to 27 ppbv in spring-summer and from 10 ppbv to 30 ppbv in autumn-winter. Monthly hourly-averaged glyoxal surface mixing ratios in the early morning show higher values during winter, 2 ppbv, than in summer, 0.7 ppbv. We also evaluated the ratio between glyoxal and formaldehyde (RGF) surface mixing ratios, as an indicator of the nature of VOCs precursors. The RGF was also correlated with the measured NO2, which represents a direct signal of anthropogenic emissions, along with the VOCs emission inventories in Madrid. The RGF results yielded higher ratios in spring, 0.1–0.13, than in winter and autumn (in the range of 0.02–0.07) when NO2 levels were higher.

Co-delivery of paclitaxel and cisplatin in poly(2-oxazoline) polymeric micelles: Implications for drug loading, release, pharmacokinetics and outcome of ovarian and breast cancer treatments

Concurrent delivery of multiple drugs using nanoformulations can improve outcomes of cancer treatments. Here we demonstrate that this approach can be used to improve the paclitaxel (PTX) and alkylated cisplatin prodrug combination therapy of ovarian and breast cancer. The drugs are co-loaded in the polymeric micelle system based on amphiphilic block copolymer poly(2-methyl-2-oxazoline-block-2-butyl-2-oxazoline-block-2-methyl-2-oxazoline) (P(MeOx-b-BuOx-b-MeOx). A broad range of drug mixing ratios and exceptionally high two-drug loading of over 50 wt.% drug in a stable micellar solution is demonstrated. The drugs co-loading in the micelles result in a slowed-down release to serum, improved pharmacokinetics and increased tumor distribution for both drugs. A superior anti-tumor activity of co-loaded PTX/CP drug micelles compared to single drug micelles or their mixture was demonstrated in cisplatin-resistant human ovarian carcinoma A2780/CisR xenograft tumor and multidrug resistant breast cancer LCC-6-MDR orthotopic tumor models. The improved tumor delivery of co-loaded drugs was related to decreased drug release rates as confirmed by simulation for micelle, serum and tumor compartments in a three-compartmental model. Overall, the results provide support for the use of PTX and cisplatin co-loaded micelles as a strategy for improved chemotherapy of ovarian and breast cancer and potential for the clinical translation.

Synthesis of pollucite with Cs-polluted incineration ash mixed with soil for immobilization of radioactive Cs

The Fukushima unclear leakage in Japan on March 11 t h, 2011 resulted in huge amount of Cs-polluted incineration ashes and soils produced. The conventional solidification (cement and glass solidifications etc.) methods for nuclear wastes treatment seem unsuitable because too many solidification basis materials are also required. A novel hydrothermal method therefore has been developed to directly synthesize pollucite only with Cs-polluted incineration ash and soil to immobilize Cs. The results revealed that pollucite could be synthesized with a wide range of mixing ratios between incineration ash (PA) and soil (kaolin) even at a lower temperature (≥140 °C) for a shorter time (≥3 h), and however a higher temperature or a longer time favored to form pure pollucite. Moreover, the synthesized pollucite specimens possessed a high strength (flexural strength>16 MPa), suggesting that this hydrothermal synthesis might have the potential for treatment of Cs-polluted incineration ash and soil. The Extended X-ray Absorption Fine Structure (EXAFS) analyses further revealed that the polluted Cs did be immobilized into the structure of the synthesized pollucite rather than physically adsorbed in the pores. Leaching tests also demonstrated that the amount of Cs leached from the synthesized pollucite specimens was very low, similar to that of ceramic immobilization.

Hydrogen-rich syngas produced from co-gasification of wet sewage sludge and torrefied biomass in self-generated steam agent

A synergistic scheme of co-gasification of wet sewage sludge and torrefied biomass was proposed in order to get the hydrogen-rich syngas, which could avoid the dual energy input for drying of wet sewage sludge and steam generation. Co-gasification behavior of wet sewage sludge and torrefied biomass was evaluated by using a general non-stoichiometric thermodynamic equilibrium model developed based upon the Gibbs free energy minimization. The tenary plot of CHO system was used to evaluate the theoretical carbon formation performance at thermodynamic equilibrium state. The effects of mixing ratio and torrefaction severity on carbon conversion ratio, compositions of dry syngas, and H2 yield were also addressed. High mixing ratio of wet sewage sludge and high gasification temperature were required for the high carbon conversion ratio. The gasification temperature of 1100 K was a favorable level for the H2 yield and energy input. The optimal mixing ratio range of wet sewage sludge for low and middle temperatures torrefied biomass samples was between 30% and 40%, while that for high temperature ones was approximately 55%. This work could provide a feasible technical route and basic data for the resource and energy utilization of sewage sludge and biomass.

(Invited) Gel Behavior of Sugar-Based Polymers and Their Composites

Cellulose is a linear sugar-based polymer and a main component of wood pulp which are a material of paper. In this decade, the cellulose nano-fibers are gathering attentions in the material science because of their mechanical properties and environmental suitability. In particular, the 2,2,6,6-tetramethyl-1-piperdinyloxy free radical (TEMPO)-oxidized cellulose nano-fiber (TOCNF) is the ultrafine fiber and have many carboxyl groups on its surface, which are suitable for the chemical modifications. From this viewpoint, we have examined the modifications of TOCNF to develop absorbers. It was demonstrated that the nanocomposites of nanoparticle/dendrimer/TOCNF allowed the diffusion of small molecules in their matrix, although the simple TOCNF formed a film with powerful gas-barrier function. Thus, the availability of these nanocomposites for absorbers were verified; however, the detailed structures of these nanocomposites were not yet confirmed. In this study, The TOCNF was hybridized with amine-polymers (poly(amido amine) dendrimer and poly(ethyleneimine) with different molecular weights). The hybrids formed transparent gels, and especially the dendrimer led to a homogeneous viscoelastic gelation in the wide range of mixing ratio. The number binding ratios of polymers per TOCNF suggested that the dendrimer partially covered the surface of TOCNF, facilitating the cross-linking, while the poly(ethyleneimine) could vary their conformations to cover the TOCNF at the different concentrations.

Perturbing the spin crossover transition activation energies in Fe(H2B(pz)2)2(bipy) with zwitterionic additions

A thermal component to the soft x-ray induced spin crossover transition exists in the switching of a spin crossover compound (complex [Fe{H2B(pz)2}2(bipy)] (pz = pyrazol-1-yl, bipy = 2,2′-bipyridine) combined with the dipolar molecular additives (zwitterionic p-benzoquinonemonoimine C6H2()2()2). The addition of the zwitterionic molecule locks the Fe(II) complex in a largely low spin state configuration over an unusually broad temperature range that includes temperatures well above the thermal spin crossover temperature of 160 K. It is demonstrated here that the process of exciting the [Fe{H2B(pz)2}2(bipy)] moiety, in the presence of with C6H2()2()2, to an electronic state characteristic of the high spin state though incident x-ray fluences, has a thermal activation energies are determined to 14–18 meV for a range of mixing ratios from 1:2 to 1:10. Those activation energies are also significantly reduced as compared to values of 60–80 meV found for nanometer thin films of [Fe{H2B(pz)2}2(bipy)] on SiO2.

Drug Combination Synergy in Worm-like Polymeric Micelles Improves Treatment Outcome for Small Cell and Non-Small Cell Lung Cancer.

Nanoparticle-based systems for concurrent delivery of multiple drugs can improve outcomes of cancer treatments, but face challenges because of differential solubility and fairly low threshold for incorporation of many drugs. Here we demonstrate that this approach can be used to greatly improve the treatment outcomes of etoposide (ETO) and platinum drug combination ("EP/PE") therapy that is the backbone for treatment of prevalent and deadly small cell lung cancer (SCLC). A polymeric micelle system based on amphiphilic block copolymer poly(2-oxazoline)s (POx) poly(2-methyl-2-oxazoline- block-2-butyl-2-oxazoline- block-2-methyl-2-oxazoline) (P(MeOx- b-BuOx- b-MeOx) is used along with an alkylated cisplatin prodrug to enable co-formulation of EP/PE in a single high-capacity vehicle. A broad range of drug mixing ratios and exceptionally high two-drug loading of over 50% wt. drug in dispersed phase is demonstrated. The highly loaded POx micelles have worm-like morphology, unprecedented for drug loaded polymeric micelles reported so far, which usually form spheres upon drug loading. The drugs co-loading in the micelles result in a slowed-down release, improved pharmacokinetics, and increased tumor distribution of both drugs. A superior antitumor activity of co-loaded EP/PE drug micelles compared to single drug micelles or their combination as well as free drug combination was demonstrated using several animal models of SCLC and non-small cell lung cancer.

Stringent upper limit of CH4 on Mars based on SOFIA/EXES observations

Discovery of CH4 in the Martian atmosphere has led to much discussion since it could be a signature of biological and/or geological activities on Mars. However, the presence of CH4 and its temporal and spatial variations are still under discussion because of the large uncertainties embedded in the previous observations. We performed sensitive measurements of Martian CH4 by using the Echelon-Cross-Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) on 16 March 2016, which corresponds to summer (Ls = 123.2∘) in the northern hemisphere on Mars. The high altitude of SOFIA (~13.7 km) enables us to significantly reduce the effects of terrestrial atmosphere. Thanks to this, SOFIA/EXES improves our chances of detecting Martian CH4 lines because it reduces the impact of telluric CH4 on Martian CH4, and allows us to use CH4 lines in the 7.5 μm band which has less contamination. However, our results show no unambiguous detection of Martian CH4. The Martian disk was spatially resolved into 3 × 3 areas, and the upper limits on the CH4 volume mixing ratio range from 1 to 9 ppb across the Martian atmosphere, which is significantly less than detections in several other studies. These results emphasize that release of CH4 on Mars is sporadic and/or localized if the process is present.

Enrichment of intact phosphoproteins using immobilized titanium(IV) affinity chromatography microspheres

AbstractApproximately a third of eukaryotic proteins are estimated to be phosphorylated, and the protein phosphorylation is significant in regulating almost all aspects of cell life. Due to low stoichiometry of phosphorylation, efficient enrichment is often an essential step in phosphoproteomics study. Over the decades, lots of enrichment materials have been successfully developed and widely used for intact phosphoproeins. One of these materials is immobilized titanium(IV) affinity chromatography (Ti4+‐IMAC) microspheres, which has been widely studied and used for phosphopeptides enrichment. Application of Ti4+‐IMAC for intact phosphoprotein enrichment has also proven possible, where intact phosphoproteins (α‐casein and β‐casein) were successfully enrichment out of their mixture with BSA (1:1:10, w/w). Here we report our detailed investigation of intact phosphoprotein enrichment using Ti4+‐IMAC. With BSA and standard intact phosphoprotein β‐casein, selectivity with a wide range of mixing ratios of 1:1, 1:100, 1:500, 1:1000 and 1:2000 (β‐casein:BSA, w/w) and binding capacity were investigated; the enrichment capability of Ti4+‐IMAC was further investigated with real biological systems, including non‐fat milk, egg white and swine liver tissue extract. The results show that Ti4+‐IMAC is a promising material for intact phosphoprotein enrichment.

Effect of dynamic interfacial dilational properties on the foam stability of catanionic surfactant mixtures in the presence of oil

The dynamic interfacial dilational properties of catanionic surfactant mixtures and the relationship with foam stability in the presence of oil are studied in the present work. The dynamic interfacial dilational properties of catanionic mixtures at aqueous-oil interface have been studied by means of oscillating the drop profile method. The mixing ratio of anionic/cationic surfactants and the hydrophobic chain length of the surfactants influence the foam stability in the presence of oil through the interfacial dilational properties. Over a wide range of mixing ratio of SDS/C12TAB, interfacial tension and dilational modulus of the catanionic mixtures reaches similar equilibrium values. But as the mixing ratio approaches 1:1, comparable anionic and cationic surfactants are adsorbed at interface. This significantly speeds up the dynamic adsorption progress, which benefits the fast foaming progress. In addition, the increase of the alkyl chain length of CnTAB in SDS-CnTAB (n = 8, 10, 12, 14, 16) mixtures enhances the equilibrium modulus, but slows down the dynamic adsorption progress. Thus the foamability and stability decreases when surfactants have overlong hydrophobic chains. Overall, the fast generation of a tightly packed interfacial layer is in favor of the foamability and foam stability in the presence of oil.

An experimental study of multimodal glass suspension rheology to test and validate a polydisperse suspension viscosity model

Experimental measurements of non-colloidal multimodal suspension viscosities are performed over a wide range of mixing ratios and used to test the robustness and predictive capability of a recent viscosity model (Mwasame et al. in Phys Fluids 28:061701, 2016b), subsequently referred to as the MWB model. Three unimodally distributed particle suspensions with narrow size distributions are blended to make the bimodal and trimodal suspensions used in the rheological experiments. We demonstrate how predictions for mixture viscosities can be made using the MWB model only requiring the volume-weighted average particle sizes and viscosity correlations of the individual unimodal suspensions comprising the blend. The resultant model predictions are found to be in good agreement with measured bimodal and trimodal viscosity data to within expected experimental uncertainty. The datasets provided here can be used to validate future modeling efforts, and the MWB model can be used to optimize the viscosity of multimodal suspension mixtures for specific performance criteria.

Co-pyrolysis of lignocellulosic biomass and microalgae: Products characteristics and interaction effect

Co-pyrolysis of biomass has a potential to change the quality of pyrolytic bio-oil. In this work, co-pyrolysis of bamboo, a typical lignocellulosic biomass, and Nannochloropsis sp. (NS), a microalgae, was carried out in a fixed bed reactor at a range of mixing ratio of NS and bamboo, to find out whether the quality of pyrolytic bio-oil was improved. A significant improvement on bio-oil after co-pyrolysis of bamboo and NS was observed that bio-oil yield increased up to 66.63wt% (at 1:1) and the content of long-chain fatty acids in bio-oil also dramatically increased (the maximum up to 50.92% (13.57wt%) at 1:1) whereas acetic acid, O-containing species, and N-containing compounds decreased greatly. Nitrogen transformation mechanism during co-pyrolysis also was explored. Results showed that nitrogen in microalgae preferred to transform into solid char and gas phase during co-pyrolysis, while more pyrrolic-N and quaternary-N generated with diminishing protein-N and pyridinic-N in char.

Application of adhesively bonded single lap joints for fracture assessment of adhesive materials

ABSTRACTIn this study, a method has been proposed to obtain the failure envelope of brittle adhesives using the experimental failure loads of precracked single lap joints (SLJs). The proposed technique is based on the principles of linear elastic fracture mechanics (LEFM), on J-integral relations, and on results of a numerical analysis. Compared to the previous approaches, the introduced experimental method has some advantages such as low manufacturing costs and simpler test procedure. The proposed method can also provide a wide range of mode mix ratios without the need of an additional apparatus. The fracture envelope obtained from the proposed method was then verified by performing some fracture tests including double cantilever beam (DCB), end-notched flexure (ENF), and single leg bending (SLB) specimens. Good correlation was seen between the fracture envelopes of the proposed method and the ones obtained from the fracture mechanics experiments.

Carbon Monoxide Affecting Planetary Atmospheric Chemistry

Abstract CO is an important component in many atmospheres, including Titan, Triton, and Pluto, and has also been detected in the atmosphere of a number of exoplanets. Numerous experimental simulations have been carried out in the laboratory to understand the chemistry in atmospheres, but very few simulations have included CO in the initial gas mixtures. The effect of CO on the chemistry occurring in these atmospheres is still poorly understood. We have investigated the effect of CO on both gas and solid phase chemistry in a series of planetary atmosphere simulation experiments using gas mixtures of CO, , and with a range of CO mixing ratios from 0.05% to 5% at low temperature (∼100 K). We find that CO affects the gas phase chemistry, the density, and the composition of the solids. Specifically, with the increase of CO in the initial gases, there is less but more , HCN, , and produced in the gas phase, while the density, oxygen content, and degree of unsaturation of the solids increase. The results indicate that CO has an important impact on the chemistry occurring in our experiments and accordingly in planetary atmospheres.

Saltwater intrusion as potential driver of phosphorus release from limestone bedrock in a coastal aquifer

An important but often overlooked consequence of saltwater intrusion is the potential increase of groundwater soluble reactive phosphorus concentrations. The phosphorus sorption dynamics of two limestone rocks of different composition were investigated by simulating seawater intrusion over a wide range of mixing ratios between freshwater and saltwater. Both rocks exhibited a logarithmic loss of sorption efficiency in mixtures containing more than approximately 3 mM Cl− concentration (100 mg Cl−/L; about <1% saltwater). We infer that aquifer solids immersed in freshwater would undergo phosphorus desorption in response to the introduction of this minor amount of seawater. This Cl− concentration is within the range designated as fresh water. Thus we conclude that increased soluble reactive phosphorus availability from saltwater-induced desorption may occur at the ion exchange front, which is actually landward of the saltwater intrusion front as it is commonly defined. Sorption efficiency in our experiments continued to decline as salinity increased, until Cl− concentration reached a second threshold of 50 or 200 mM (1700 or 7700 mg Cl−/L), depending on the rock composition, particularly iron content. Further increase in salinity would produce little increase in groundwater soluble reactive phosphorus concentration. Our results have implications for soluble reactive phosphorus availability in estuaries that receive mixing zone groundwater discharge.

Influence of Z-pin embedded length on the interlaminar traction response of multi-directional composite laminates

The work in this paper investigated the performance of composites through-thickness reinforcing Z-pins as a function of their embedded length in pre-preg laminates. Single Z-pins were inserted into multidirectional carbon fibre laminates with increasing thicknesses, corresponding to embedded lengths from 1mm to 10mm and tested through a range of mixed mode displacement ratios to investigate their interlaminar bridging traction response. Detailed analysis of the tests revealed a non-linear tangential friction response and its strong dependence on the embedded length of the Z-pin. Using a new power law empirical relationship for the tangential friction force per unit length, a modified Z-pin bridging traction analytical model was proposed, giving good predictions of the full mixed mode bridging mechanics of a CFRP Z-pin in a multidirectional composite laminate of varying thickness. Several characteristics of the model are discussed and their influence on predicting the Z-pin bridging energy response have been analysed.

Response of suspended sediment particle size distributions to changes in water chemistry at an Andean mountain stream confluence receiving arsenic rich acid drainage

AbstractAcid drainage is an important water quality issue in Andean watersheds, affecting the sustainability of urban, agricultural, and industrial activities. Mixing zones receiving acid drainage are critical sites where changes in pH and chemical environment promote the formation and dissolution of iron and aluminum oxy/hydroxides. These particles can significantly change the speciation of toxic metals and metalloids throughout drainage networks via sorption, desorption, and settling processes. However, little is known about the behavior of particle size distributions (PSDs) in streams affected by acid drainage and their relationship to metal speciation. This work studied: (a) the PSDs for a wide range of mixing ratios found at a fluvial confluence affected by acid drainage, and (b) the response of PSDs and arsenic speciation to environmental changes found when the particles approach complete mixing conditions. The confluence between the Azufre River (pH ~ 2, high concentration of dissolved metals) and Caracarani River (pH = 8.6, low concentration of dissolved metals) was used as a representative model for study. Field measurements show a bimodal PSD with modal diameters of ~50 and 300 μm. At shorter distances from the junction, the smaller modes with smaller particle volumes were dominant across the stream cross‐sections. A systematic shift towards larger particle sizes and larger particle volumes occurred downstream. The analysis of laboratory PSDs for Azufre/Caracarani mixing ratios between 0.01 and 0.5 (pH from 6.2 to 2.3) showed a bimodal trend with ~15 and 50 μm characteristic diameters; larger particles formed at pH&gt;4. When particle suspensions were transferred in laboratory experiments from very low pH to full mixing conditions (pH ~ 2.8 and mixing ratio ~ 0.25) particle sizes varied, and the dissolved arsenic concentration decreased. The observed reaction kinetics were slow compared to the time scale of advective transport, creating opportunities for engineered controls for arsenic. This work contributes to a better understanding of the chemical‐hydrodynamic interactions in watersheds affected by mining, and identifying opportunities to improve water quality at points of use.

A versatile, refrigerant- and cryogen-free cryofocusing–thermodesorption unit for preconcentration of traces gases in air

Abstract. We present a compact and versatile cryofocusing–thermodesorption unit, which we developed for quantitative analysis of halogenated trace gases in ambient air. Possible applications include aircraft-based in situ measurements, in situ monitoring and laboratory operation for the analysis of flask samples. Analytes are trapped on adsorptive material cooled by a Stirling cooler to low temperatures (e.g. −80 °C) and subsequently desorbed by rapid heating of the adsorptive material (e.g. +200 °C). The set-up involves neither the exchange of adsorption tubes nor any further condensation or refocusing steps. No moving parts are used that would require vacuum insulation. This allows for a simple and robust design. Reliable operation is ensured by the Stirling cooler, which neither contains a liquid refrigerant nor requires refilling a cryogen. At the same time, it allows for significantly lower adsorption temperatures compared to commonly used Peltier elements. We use gas chromatography – mass spectrometry (GC–MS) for separation and detection of the preconcentrated analytes after splitless injection. A substance boiling point range of approximately −80 to +150 °C and a substance mixing ratio range of less than 1 ppt (pmol mol−1) to more than 500 ppt in preconcentrated sample volumes of 0.1 to 10 L of ambient air is covered, depending on the application and its analytical demands. We present the instrumental design of the preconcentration unit and demonstrate capabilities and performance through the examination of analyte breakthrough during adsorption, repeatability of desorption and analyte residues in blank tests. Examples of application are taken from the analysis of flask samples collected at Mace Head Atmospheric Research Station in Ireland using our laboratory GC–MS instruments and by data obtained during a research flight with our in situ aircraft instrument GhOST-MS (Gas chromatograph for the Observation of Tracers – coupled with a Mass Spectrometer).

Quantitative Decoding of Complex Gas Mixtures Using Mixed-Potential Sensor Arrays

Advances in sensor technologies are required to go beyond the limitations of current commercial sensors and enable advanced combustion and emission control for fuel-saving lean-burn and low temperature combustion (LTC) engines. Oxygen l-sensors are an integral part of on-board diagnostics (OBD) of today’s spark-ignition vehicle emission systems, but a suitable analog is not available for NOx, NH3 and NMHC detection to control after-treatment systems and perform OBD functions in lean-burn engines. Mixed-potential sensors fabricated via well-established commercial manufacturing methods present a promising avenue to enable the widespread utilization of NOx, NH3 and NMHC sensing technology. Los Alamos National Lab (LANL) has developed patented pre-commercial prototype mixed-potential sensors exhibiting strong preferential selectivity and sensitivity to these target emission constituents. However, a single device with absolute selectivity remains elusive (1-3). The work herein presents an alternative strategy to absolute selectivity, in which the cross-sensitivity of a set of sensor elements run at varying operating conditions is exploited through the use of Bayesian inference techniques based on physical models of sensor-analyte interactions. We have previously shown that the individual concentration of each analyte species in NH3/C3H6 mixtures can be uniquely determined from the sensor voltage response of a single sensor operating at four different current bias points by employing a Bayesian interference model (4). This model was recently extended to de-convolute the gas speciation of NO/C3H8 mixtures utilizing the voltage response from two sensors of different electrode composition, LSCr|YSZ|Pt and Au|YSZ|Pt. In this work, we seek to further explore the mixed-potential array concept by employing multiple sensors in order to uniquely identify the concentration of NO, NO2, NH3, and C3H8 in complex mixtures relevant to diesel exhaust. Sensor voltage response data collected on a wide range of mixing ratios are used to train the Bayesian model. Gas mixtures not used in the training set are then used to test the accuracy of the model. This research represents the first stages of developing miniaturized mixed-potential electrochemical sensor (MPES) arrays as an all-in-one NOx/NH3/NMHC sensor package that will provide quantitative emissions monitoring and OBD for all lean-burn engine applications. Acknowledgements The research was funded by the Los Alamos National Laboratory Directed Research Development Exploratory Research (LDRD-ER) program.

A CHARACTERISTIC TRANSMISSION SPECTRUM DOMINATED BY H2O APPLIES TO THE MAJORITY OF HST/WFC3 EXOPLANET OBSERVATIONS

ABSTRACT Currently, 19 transiting exoplanets have published transmission spectra obtained with the Hubble/WFC3 G141 near-IR grism. Using this sample, we have undertaken a uniform analysis incorporating measurement-error debiasing of the spectral modulation due to H2O, measured in terms of the estimated atmospheric scale height, . For those planets with a reported H2O detection (10 out of 19), the spectral modulation due to H2O ranges from 0.9 to 2.9 with a mean value of 1.8 ± 0.5 . This spectral modulation is significantly less than predicted for clear atmospheres. For the group of planets in which H2O has been detected, we find the individual spectra can be coherently averaged to produce a characteristic spectrum in which the shape, together with the spectral modulation of the sample, are consistent with a range of H2O mixing ratios and cloud-top pressures, with a minimum H2O mixing ratio of ppm corresponding to the cloud-free case. Using this lower limit, we show that clouds or aerosols must block at least half of the atmospheric column that would otherwise be sampled by transmission spectroscopy in the case of a cloud-free atmosphere. We conclude that terminator-region clouds with sufficient opacity to be opaque in slant-viewing geometry are common in hot Jupiters.