Constraints on Pluto’s H and CH₄ profiles from New Horizons Alice Lyα observations

The Alice spectrograph on New Horizons performed several far-ultraviolet (FUV) airglow observations during the July 2015 flyby of Pluto. One of these observations, named PColor2, was a short (226 s) scan across the dayside disk of Pluto from a range of ∼34,000 km, at about 40 minutes prior to closest approach. The brightest observed FUV airglow signal at Pluto is the Lyman alpha (Lyα) emission line of atomic hydrogen, which arises primarily through the resonant scattering of solar Lyα by H atoms in the upper atmosphere, with a brightness of about 30 Rayleighs. Pluto appears dark against the much brighter (∼100 Rayleigh) sky background; this sky background is likewise the result of resonantly scattered solar Lyα, in this case by H atoms in the interplanetary medium (IPM). Here we use an updated photochemical model and a resonance line radiative transfer model to perform detailed simulations of the Lyα emissions observed in the Alice PColor2 scan. The photochemical models show that H and CH₄ abundances in Pluto’s upper atmosphere are a very strong function of the near-surface mixing ratio of CH₄, and could provide a useful way to remotely monitor seasonal climate variations in Pluto’s lower atmosphere. The morphology of the PColor2 Lyα emissions provides constraints on the current abundance profiles of H atoms and CH₄ molecules in Pluto’s atmosphere, and indicate that the globally averaged near-surface mixing ratio of CH₄ is currently close to 0.4%. This new result thus provides independent confirmation of one of the primary results from the solar occultation, also observed with the New Horizons Alice ultraviolet spectrograph

Constraints on Pluto’s H and CH₄ profiles from New Horizons Alice Lyα observations

The Alice spectrograph on New Horizons performed several far-ultraviolet (FUV) airglow observations during the July 2015 flyby of Pluto. One of these observations, named PColor2, was a short (226 s) scan across the dayside disk of Pluto from a range of ∼34,000 km, at about 40 minutes prior to closest approach. The brightest observed FUV airglow signal at Pluto is the Lyman alpha (Lyα) emission line of atomic hydrogen, which arises primarily through the resonant scattering of solar Lyα by H atoms in the upper atmosphere, with a brightness of about 30 Rayleighs. Pluto appears dark against the much brighter (∼100 Rayleigh) sky background; this sky background is likewise the result of resonantly scattered solar Lyα, in this case by H atoms in the interplanetary medium (IPM). Here we use an updated photochemical model and a resonance line radiative transfer model to perform detailed simulations of the Lyα emissions observed in the Alice PColor2 scan. The photochemical models show that H and CH₄ abundances in Pluto’s upper atmosphere are a very strong function of the near-surface mixing ratio of CH₄, and could provide a useful way to remotely monitor seasonal climate variations in Pluto’s lower atmosphere. The morphology of the PColor2 Lyα emissions provides constraints on the current abundance profiles of H atoms and CH₄ molecules in Pluto’s atmosphere, and indicate that the globally averaged near-surface mixing ratio of CH₄ is currently close to 0.4%. This new result thus provides independent confirmation of one of the primary results from the solar occultation, also observed with the New Horizons Alice ultraviolet spectrograph

Origin and Health Impacts of Emissions of Toxic By-Products and Fine Particles from Combustion and Thermal Treatment of Hazardous Wastes and Materials

High-temperature, controlled incineration and thermal treatment of contaminated soils, sediments, and wastes at Superfund sites are often preferred methods of remediation of contaminated sites under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 and related legislation. Although these methods may be executed safely, formation of toxic combustion or reaction by-products is still a cause of concern. Emissions of polycyclic aromatic hydrocarbons (PAHs); chlorinated hydrocarbons (CHCs), including polychlorinated dibenzo-p-dioxins and dibenzofurans; and toxic metals (e.g., chromium VI) have historically been the focus of combustion and health effects research. However, fine particulate matter (PM) and ultrafine PM, which have been documented to be related to cardiovascular disease, pulmonary disease, and cancer, have more recently become the focus of research. Fine PM and ultrafine PM are effective delivery agents for PAHs, CHCs, and toxic metals. In addition, it has recently been realized that brominated hydrocarbons (including brominated/chlorinated dioxins), redox-active metals, and redox-active persistent free radicals are also associated with PM emissions from combustion and thermal processes. In this article, we discuss the origin of each of these classes of pollutants, the nature of their association with combustion-generated PM, and the mechanisms of their known and potential health impacts

Venus Thermospheric CO and Temperature Deduced From Cassini UVIS Airglow Measurements

Cassini UVIS measurements of Venus\u27s dayside airglow show prominent CO Fourth Positive bands, as well as other CO bands and atomic and ionic emissions from H, O, C, N, He, O+, C+, and C++. The Fourth Positive bands are excited by photon and photoelectron impact dissociative excitation of CO2, dissociative recombination of CO2+, photoelectron impact on CO, and fluorescent scattering of solar FUV (including Lyman-alpha). These mechanisms each produce a characteristic distribution of vibrational levels in the upper state, and in addition the dissociative processes yield CO molecules at higher rotational temperatures than do the processes acting directly on CO. Solar Lyman-alpha pumps the v\u27 = 14 level of the upper state, and because Lyman-alpha penetrates to the CO2 absorbing level below 120km, the v\u27 = 14 sequence is sensitive to CO densities at much lower altitudes than the bulk of the Fourth Positive emissions. We have constructed a model of the emission of these bands incorporating the above mechanisms and using the VTS3 model of thermospheric composition. We will present the preliminary results of our analysis of the relative importance of the various excitation processes and the distribution of CO in the morning equatorial thermosphere, with attention paid to the apparent wave structure (wavelength 2000 km) seen in the raw data

Venus Thermospheric CO and Temperature Deduced From Cassini UVIS Airglow Measurements

Cassini UVIS measurements of Venus\u27s dayside airglow show prominent CO Fourth Positive bands, as well as other CO bands and atomic and ionic emissions from H, O, C, N, He, O+, C+, and C++. The Fourth Positive bands are excited by photon and photoelectron impact dissociative excitation of CO2, dissociative recombination of CO2+, photoelectron impact on CO, and fluorescent scattering of solar FUV (including Lyman-alpha). These mechanisms each produce a characteristic distribution of vibrational levels in the upper state, and in addition the dissociative processes yield CO molecules at higher rotational temperatures than do the processes acting directly on CO. Solar Lyman-alpha pumps the v\u27 = 14 level of the upper state, and because Lyman-alpha penetrates to the CO2 absorbing level below 120km, the v\u27 = 14 sequence is sensitive to CO densities at much lower altitudes than the bulk of the Fourth Positive emissions. We have constructed a model of the emission of these bands incorporating the above mechanisms and using the VTS3 model of thermospheric composition. We will present the preliminary results of our analysis of the relative importance of the various excitation processes and the distribution of CO in the morning equatorial thermosphere, with attention paid to the apparent wave structure (wavelength 2000 km) seen in the raw data

Cassini UVIS Observations of Saturn's Auroras and Polar Haze

In 2016 and 2017, the Cassini Saturn Orbiter executed a final series of high inclination, low- periapsis orbits ideal for studying Saturn's polar regions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) obtained an extensive set of auroral images of both poles, some at the highest spatial resolution obtained during Cassini's long orbital mission (2004-2017). In some cases, two or three spacecraft slews at right angles to the long slit of the spectrograph were required to cover the entire auroral region to form images of auroral H2 and H emission. The long wavelength part of the northern UVIS polar images contains a signal from reflected sunlight with absorption signatures of acetylene and other Saturn hydrocarbons. Saturn's UV-dark polar hexagon is now seen in the new UVIS long- wavelength data, surrounded by a circular collar that is less dark. There is a definite spatial relationship between the UV-bright auroras and the dark material, with the dark material concentrated under or just inside of the main auroral oval. The outer dark collar roughly corresponds with the previously reported weaker outer auroral oval (Grodent et al., 2011; Lamy et al., 2013). Time variations in the dark material are seen. The spectroscopy of the different regions will be discussed. As has been previously discussed using Voyager data (Lane et al., 1982, West et al., 1983, Pryor and Hord, 1991), Hubble data (Ben Jaffel et al., 1995; Gerard et al., 1995) and Cassini data (Sayanagi et al., 2018), Saturn's auroras appear to be generating, through both neutral and ion chemistry, UV-dark material that is probably composed of complex hydrocarbons

scopic evidence for high altitude aurora at Jupiter from Galileo extreme ultraviolet spectrometer and Hopkins ultraviolet telescope observations

The Galileo Extreme Ultraviolet Spectrometer (EUVS) and th