Effect of petrochemical industrial emissions of reactive alkenes and NO\u3csub\u3ex\u3c/sub\u3e on tropospheric ozone formation in Houston, Texas

Petrochemical industrial facilities can emit large amounts of highly reactive hydrocarbons and NOx to the atmosphere; in the summertime, such colocated emissions are shown to consistently result in rapid and efficient ozone (O3) formation downwind. Airborne measurements show initial hydrocarbon reactivity in petrochemical source plumes in the Houston, TX, metropolitan area is primarily due to routine emissions of the alkenes propene and ethene. Reported emissions of these highly reactive compounds are substantially lower than emissions inferred from measurements in the plumes from these sources. Net O3 formation rates and yields per NOx molecule oxidized in these petrochemical industrial source plumes are substantially higher than rates and yields observed in urban or rural power plant plumes. These observations suggest that reductions in reactive alkene emissions from petrochemical industrial sources are required to effectively address the most extreme O3 exceedences in the Houston metropolitan area

A Small Mission Featuring an Imaging X-ray Polarimeter with High Sensitivity

We present a detailed description of a small mission capable of obtaining high precision and meaningful measurement of the Xray polarization of a variety of different classes of cosmic Xray sources. Compared to other ideas that have been suggested this experiment has demonstrated in the laboratory a number of extremely important features relevant to the ultimate selection of such a mission by a funding agency. The most important of these questions are: 1) Have you demonstrated the sensitivity to a polarized beam at the energies of interest (i.e. the energies which represent the majority (not the minority) of detected photons from the Xray source of interest? 2) Have you demonstrated that the device's sensitivity to an unpolarized beam is really negligible and/or quantified the impact of any systematic effects upon actual measurements? We present our answers to these questions backed up by laboratory measurements and give an overview of the mission

Laboratory studies of astrophysical ices

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. This thesis reports the results of three laboratory studies, each concerned with some aspect of ices in an astrophysical environment, presented as independent papers: 1. Molecular hydrogen is the most abundant molecule in interstellar space, and is therefore of central importance to the physics and chemistry of that environment. Experiments simulating the codeposition of molecular hydrogen and water ice on interstellar grains demonstrate that amorphous water ice at 12 K can incorporate a substantial amount of H2, up to a mole ratio of H2/H2O = 0.53. We find that the physical behavior of ~80% of the hydrogen can be explained satisfactorily in terms of an equilibrium population, thermodynamically governed by a wide distribution of binding site energies. Such a description predicts that gas phase accretion could lead to mole fractions of H2 in interstellar grain mantles as high as 0.3. Accretion of gas phase H2 onto grain mantles, rather than photochemical production of H2 within the ice, could be a general explanation for recent observations of frozen H2 in interstellar ices. The possibility of interstellar grains that are rich in H2 could strongly affect our understanding of grain surface chemistry and gas-grain interactions. 2. Photochemical models of Triton's atmosphere predict ethylene (C2H4) as a primary product of methane photodissociation, formed at a high enough level that it should be readily observable as a surface condensate in [...] years, yet it has not been observed. Ultraviolet photolysis experiments on C2H4 ice were done to simulate its irradiation on Triton's surface. Our results show that C2H4 ice is readily dissociated by radiation of wavelengths [...], with C2H4 ice as a primary product. Dilution in an inert N2 matrix does not affect the photochemical yield of C2H4, suggesting that the reaction C2H4 [...] C2H2 is unimolecular. Quantum yields for both the destruction of C2H4 and the formation of C2H2 are discussed, as functions of both irradiation wavelength and dilution in N2 ice. Applying these results to Triton, we find that the ambient UV flux reaching Triton's surface is more than adequate to prevent the build-up of an ethylene ice layer. 3. Thermal models of icy satellite surfaces that allow the scattering and absorption of incident sunlight at significant depths predict an enhancement of subsurface temperatures over the mean surface temperature known as the solid-state greenhouse effect. We verify that a solid-state greenhouse can readily be produced in a bed of evacuated glass beads, used as a crude analog for the surface of an icy body. Measurements of the thermal and radiative properties thought to govern the size of this temperature enhancement confirm that it can be reasonably predicted from these parameters

Deuterium in the Solar System

A survey of the abundances of deuterium in planetary atmospheres and small bodies has been carried out. The observed pattern of D/H ratios in the solar system may be interpreted in terms of a few simple concepts: origin, fractionation, and dilution. There appear to be two distinct reservoirs of hydrogen in the solar nebula: the bulk of hydrogen as H_2, and a smaller amount in ices and organics. The latter reservoir is characterized by a higher D/H ratio than the former, and may be the principal source of hydrogen to the terrestrial planets and small bodies. The evolution of planetary atmospheres over the age of the solar system has resulted in substantial changes in the D/H ratio in the atmospheres of the terrestrial planets. In the giant planets the abundance of D is dominated by the primordial HD, and there has been negligible chemical evolution since formation. Quantitative modeling of the D/H ratio in the solar system remains hampered by the lack of appropriate chemical kinetics data

The Kon-Tiki Mission Demonstrating Large Solar Sails for Deep Space Missions

Two key NASA strategic documents, Our Dynamic Space Environment: Heliophysics Science and Technology Roadmap for 2014-2033 and 2013 Solar and Space Physics: Science for a Technological Society, contain over a dozen references describing the value of solar sails to enable revolutionary new observational capabilities. Based on these needs, the NASA Marshall Space Flight Center (MSFC) developed the Kon-Tiki mission concept to mature solar sail technology for use in future Heliophysics missions, as well as missions of interest across a broad user community (e.g., space weather and Earth polar observatories). Kon-Tiki would serve as a pathfinder for missions that observe the solar environment from unique vantage points such as the Solar Polar Imager (SPI), opening a fundamentally new range of observational capabilities for the Heliophysics Program and for space weather monitoring. Observations away from the Sun-Earth line (SEL) present unique opportunities for answering the outstanding science questions of Heliophysics, for improving space-weather monitoring and prediction, and for revealing new discoveries about our Sun and solar system. High solar inclinations are particularly compelling. Investment in, and demonstration of, the technology needed to enable polar missions is essential to making this unique vantage point a reality in the next decade. Propellantless solar sails can be used to create artificial equilibria and indefinite station-keeping at locations sunward of L1 along the SEL, or at any desired offset from the SEL leading or trailing the Earth in its orbit. They can change the heliocentric inclination of a spacecraft from the ecliptic to as high as solar polar, stopping and remaining at any intermediate inclination orbit in between. Sails can be used to hover over the Earths poles, using solar photon pressure to offset the Earths gravitational attraction, creating functional equivalents of geostationary earth orbits. The Kon-Tiki mission would fly a small spacecraft with a large (>1200 square meter) solar sail containing embedded reflectivity control devices (RCDs) and photovoltaic cells. The mission concept includes successful deployment of the solar sail, validation of all sail subsystems, controlled station-keeping inside of the Sun-Earth L1 point, attitude control of the sail with the RCDs (including spinning and despinning), demonstration of pointing performance for science imaging, and finally an increase in heliocentric inclination (out of the ecliptic)

Planetary polarization nephelometer

We have proposed to develop a polarization nephelometer for use on future planetary descent probes. It will measure both the scattered intensity and polarization phase functions of the aerosols it encounters descending through an atmosphere. These measurements will be taken at two wavelengths separated by about an octave, with one light source near 500nm and another near 1mum. Adding polarization measurements to the intensity phase functions greatly increases our ability to constrain the size distribution, shape and chemical composition of the sampled particles. There remain important questions about these parameters of the aerosols on Venus, the giant planets and Titan that can only be addressed with a nephelometer like ours. The NRC Planetary Sciences Decadal Survey has identified probe missions to Venus and Jupiter as a priority. On both of these missions, our proposed instrument would be an excellent candidate for flight. We also expect that future probe missions to Saturn, Uranus, Neptune or Titan would employ our instrument. It could also find use in Earth in situ aerosol studies. We will use a technique to simultaneously measure intensity and polarization phase functions that uses polarization modulation of a light source. This technique has been implemented in laboratory settings, but not with considerations to the environment on a planetary descent probe. We have proposed to design and build a flexible breadboard nephelometer to test the components and concepts of our approach. We would then test the device against well defined aerosols, ensuring that it accurately measures their expected intensity and polarization phase functions. With the knowledge gained in this flexible design, we would then design and build a breadboard polarization nephelometer more suited to integration on a planetary descent probe. To include traceability in the technical requirements of our device, we would also conduct an Observing System Simulation Experiment. In this study, we would determine what the performance trade-offs are for de-scoping each capability of our instrument. Additionally, it would aid us in optimizing the nominal design parameters to yield the most unambiguous aerosol microphysical information. All of these investigations will be carried out to enhance the likelihood of success and useful data return of our proposed instrument in its descent through a planetary atmosphere. Considerations will also be given to mass, volume, power and cost

Small Satellite Platform Imaging X-Ray Polarimetry (IXPE) Mission Concept and Implementation

The goal of the Imaging X-Ray Polarimetry Explorer (IXPE) Mission is to expand understanding of high-energy astrophysical processes and sources, in support of NASA’s first science objective in Astrophysics: “Discover how the universe works.” Polarization uniquely probes physical anisotropies—ordered magnetic fields, aspheric matter distributions, or general relativistic coupling to black-hole spin—that are not otherwise measurable. The IXPE Observatory consists of spacecraft and payload modules built up in parallel to form the Observatory during system integration and test. The payload includes three polarization sensitive, x-ray detector arrays paired with three x-ray mirror module assemblies (MMA). A deployable boom provides the correct separation (focal length) between the detector units and MMAs. This paper summarizes the IXPE mission science objectives and instrument concept, describes the Observatory implementation concept and overviews mission operations. Additional information can be found at: https://wwwastro.msfc.nasa.gov/ixpe