[1] The fate of deepwater releases of gas and oil mixtures is initially determined by solubility and volatility of individual hydrocarbon species; these attributes determine partitioning between air and water. Quantifying this partitioning is necessary to constrain simulations of gas and oil transport, to predict marine bioavailability of different fractions of the gas-oil mixture, and to develop a comprehensive picture of the fate of leaked hydrocarbons in the marine environment. Analysis of airborne atmospheric data shows massive amounts (∼258,000 kg/day) of hydrocarbons evaporating promptly from the Deepwater Horizon spill; these data collected during two research flights constrain air-water partitioning, thus bioavailability and fate, of the leaked fluid. This analysis quantifies the fraction of surfacing hydrocarbons that dissolves in the water column (∼33% by mass), the fraction that does not dissolve, and the fraction that evaporates promptly after surfacing (∼14% by mass). We do not quantify the leaked fraction lacking a surface expression; therefore, calculation of atmospheric mass fluxes provides a lower limit to the total hydrocarbon leak rate of 32,600 to 47,700 barrels of fluid per day, depending on reservoir fluid composition information. This study demonstrates a new approach for rapid-response airborne assessment of future oil spills. Citation: Ryerson, T. B., et al. (2011), Atmospheric emissions from the Deepwater Horizon spill constrain airwater partitioning, hydrocarbon fate, and leak rate, Geophys. Res. Lett., 38, L07803,

This paper presents a characterization of a commercially available position-sensitive detector of energetic ions and neutrals. The detector consists of two microchannel plates followed by a resistive position-encoding anode. The work includes measurement of absolute efficiencies of H+, He+, and O+ ions in the energy range between 250 and 5000 eV, measurement of relative detection efficiencies as a function of particle impact angle, and a simple method for accurate measurement of the time at which a particle strikes the detector.

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A chemical ionization mass spectrometer (CIMS) instrument has been developed for the fast, precise, and accurate measurement of water vapor (H₂O) at low mixing ratios in the upper troposphere and lower stratosphere (UT/LS). A low-pressure flow of sample air passes through an ionization volume containing an α-particle radiation source, resulting in a cascade of ion-molecule reactions that produce hydronium ions (H₃O⁺) from ambient H₂O. The production of H₃O⁺ ions from ambient H₂O depends on pressure and flow through the ion source, which were tightly controlled in order to maintain the measurement sensitivity independent of changes in the airborne sampling environment. The instrument was calibrated every 45 min in flight by introducing a series of H₂O mixing ratios between 0.5 and 153 parts per million (ppm, 10⁻⁶ mol mol⁻¹) generated by Pt-catalyzed oxidation of H₂ standards while overflowing the inlet with dry synthetic air. The CIMS H₂O instrument was deployed in an unpressurized payload area aboard the NASA WB-57F high-altitude research aircraft during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) mission in March and April 2011. The instrument performed successfully during seven flights, measuring H₂O mixing ratios below 5 ppm in the lower stratosphere at altitudes up to 17.7 km, and as low as 3.5 ppm near the tropopause. Data were acquired at 10 Hz and reported as 1 s averages. In-flight calibrations demonstrated a typical sensitivity of 2000 Hz ppm⁻¹ at 3 ppm with a signal to noise ratio (2 σ, 1 s) greater than 32. The total measurement uncertainty was 9 to 11%, derived from the uncertainty in the in situ calibrations

This paper reports measurements of absolute differential cross sections for elastic and for chargetransfer scattering in He -He collisions. Elastic-scattering cross sections have been determined at 1.5 keV over the laboratory angular range 0.04'-1. 0' while charge-transfer cross sections have been determined at 1.5, 2.5, and 5.0 keV over the range 0.02'-1. 0', and at 0.25 and 0.50 keV over the range 0. 02'-7. 8'. The experimental data exhibit strong oscillations over the range of angles and energies studied and are in agreement with partial-wave theory calculations using phase shifts derived from proposed forms of the gerade and ungerade He2+ interaction potentials. The experimental cross sections have also been integrated over angle to provide absolute integral cross sections.