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Stratospheric aerosols (SAs) are a variable component of the Earth's albedo that may be intentionally enhanced in the future to offset greenhouse gases (geoengineering). The role of tropospheric-sourced sulfur dioxide (SO2) in maintaining background SAs has been debated for decades without in-situ measurements of SO2 at the tropical tropopause to inform this issue. Here we clarify the role of SO2 in maintaining SAs by using new in-situ SO2 measurements to evaluate climate models and satellite retrievals. We then use the observed tropical tropopause SO2 mixing ratios to estimate the global flux of SO2 across the tropical tropopause. These analyses show that the tropopause background SO2 is about 5 times smaller than reported by the average satellite observations that have been used recently to test atmospheric models. This shifts the view of SO2 as a dominant source of SAs to a near-negligible one, possibly revealing a significant gap in the SA budget.

In the upper troposphere and lower stratosphere (UTLS), the accurate quantification of low water vapor concentrations has presented a significant measurement challenge. The instrumental uncertainties are passed on to estimates of H2O transport, cloud formation and the H2O role in the UTLS energy budget and resulting effects on surface temperatures. To address the uncertainty in UTLS H2O determination, the airborne mass spectrometer AIMS-H2O, with in-flight calibration, has been developed for fast and accurate airborne water vapor measurements. We present the new setup to measure water vapor by direct ionization of ambient air. Air is sampled via a backward facing inlet that includes a bypass flow to assure short residence times (< 0.2 s) in the inlet line, which allows the instrument to achieve a time resolution of ∼ 4 Hz. From the main inlet flow, a smaller flow is extracted into the novel pressure-controlled gas discharge ion source of the mass spectrometer. The air is directed through the gas discharge region where water molecules react to form hydronium ion clusters, H3O+(H2O)n (n= 0, 1, 2), in a complex reaction scheme similar to the reactions in the D-region of the ionosphere. These ions are counted to quantify the ambient water vapor mixing ratio. The instrument is calibrated during flight using a new calibration source based on the catalytic reaction of H2 and O2 on a Pt surface to generate a calibration standard with well defined and stable H2O mixing ratios. In order to increase data quality over a range of mixing ratios, two data evaluation methods are presented for lower and higher H2O mixing ratios respectively, using either only the H3O+(H2O) ions or the ratio of all water vapor dependent ions to the total ion current. Altogether, a range of water vapor mixing ratios from 1 to 500 ppmv (mole ratio, 10−6 mol mol−1) can be covered with an accuracy between 7 and 15 %. AIMS-H2O was deployed on two DLR research aircraft, the Falcon during CONCERT (Contrail and Cirrus Experiment) in 2011, and HALO during ML-CIRRUS (Mid-Latitude Cirrus) in 2014. The comparison of AIMS-H2O with the SHARC tunable diode laser hygrometer during ML-CIRRUS shows a very good overall agreement between both instruments for the entire campaign.

A novel buttress-root shaped ZnO tetrapod-like nanostructure and a classic tetrapod ZnO nanostructure were synthesized by a direct reaction of high-purity Zn granules with oxygen using an arc discharge method. The morphology of the products could be controlled by adjusting the oxygen partial pressure. The buttress-root shaped tetrapod-like nanostructure contains three triangular nanosheets, the diameters of nanoarms vary between 50 and 80 nm, and the angle between every two arms is about 109.5°. A nanorod-centered growth model has been proposed to explain the novel nanostructure. An ultraviolet (UV) emission band located at 389 nm (3.18 eV) and a broad blue emission band centered at 484 nm (2.57 eV) were observed at room temperature.

Flower-shaped Co-doped AlN nanorod arrays have been synthesized by a direct arc discharge method on an interface at high temperature. The diameter of the nanorods varies between 40 and 120 nm, and the length is in the order of several microns. High-resolution transmission electron microscopy observation indicates that Co-doped single-crystalline h-AlN nanorods grow along the \(\langle 10\bar{1}0\rangle\) direction. As-prepared AlN nanorods exhibit ferromagnetic behavior at temperatures of 300 K and 500 K.

The effect of Zr on the microstructure, microchemistry and coercivity of Sm(CobalCu0.08Fe0. 10Zrx)8.5 (x = 0–0.10) magnets has been systematically investigated. The presence of Zr is responsible for the formation of the lamella structure. With increasing Zr content, a cellular-like structure gradually develops while the density of the lamella phase increases. A proper Zr content (0.015–0.060 at.%) is the key to form a complete and uniform cellular structure. Microchemistry data show that the Cu content in the cell boundaries in the magnet with 0.04 at.% Zr is higher than that with 0.015 at.% Zr, although both samples have similar microstructure morphologies. Higher coercivity is obtained in samples where the domain walls (DWs) are pinned at cell boundaries. For Zr-free or higher Zr samples, DWs nucleated at grain boundaries are responsible for the reduction in coercivity. During isothermal ageing, at a fixed Zr content, the coercivity is developed with increasing ageing time. These results clearly show that Zr plays an important role in the formation of a uniform cellular structure with the right microchemistry and that a critical amount of Zr is needed for the optimum magnetic properties.

Recent studies using NO, NOy, OH and HO2 (HOx) observations have postulated acetone and convection of peroxides as significant sources of HOx in the upper troposphere (UT). This work focuses on the effect these additional HOx sources have on the modeled NOy partitioning and comparisons of the modeled NOx/NOy ratio to observations. The measured NOx/NOy ratio is usually much higher than predicted regardless of the presence of acetone in the model. The exception occurs for air parcels having low NOy and O3 values. For these air parcels the measured NOx/NOy ratio is much lower than the calculated ratio unless acetone is included in the model. In all cases acetone increases the fraction of NOy that is peroxy acetyl nitrate (PAN) from typical values of much less than 0.1 to values as high as 0.35. Including acetone also reduces the scatter in a comparison between modeled and observed NOx/NOy ratios.

In situ measurements in the engine exhaust of a Concorde supersonic aircraft in the lower stratosphere are used to constrain heterogeneous reaction rates on soot particles in a plume model. Upper limit values are obtained for the product of the reactive uptake coefficients of O3 and NO2 and the mean surface area of individual soot particles using the model and the well-established O3-N2O correlation in the lower stratosphere. The low reactivity value obtained for O3 implies that soot reactions cannot account for ozone trends in the lower stratosphere.

This paper summarizes measured photodissociation quantum yields for acetone in the 290-320 nm wavelength region for pressures and temperatures characteristic of the upper troposphere. Calculations combine this laboratory data with trace gas concentrations obtained during the NASA and NOAA sponsored Stratospheric Tracers of Atmospheric Transport (STRAT) field campaign, in which measurements of OH, HO_(2), odd-nitrogen, and other compounds were collected over Hawaii, and west of California during fall and winter of 1995/1996. OH and HO_(2) concentrations within 2 to 5 km layers just below the tropopause are ∼50% larger than expected from O_(3), CH_(4), and H_(2)O chemistry alone. Although not measured during STRAT, acetone is inferred from CO measurements and acetone-CO correlations from a previous field study. These inferred acetone levels are a significant source of odd-hydrogen radicals that can explain a large part of the discrepancy in the upper troposphere. For lower altitudes, the inferred acetone makes a negligible contribution to HO_(x) (HO+HO_(2)), but influences NO_(y) partitioning. A major fraction of HO_(x) production by acetone is through CH_(2)O formation, and the HO_(x) discrepancy can also be explained by CH_(2)O levels in the 20 to 50 pptv range, regardless of the source.

The generation of sulfuric acid aerosols in aircraft exhaust has emerged as a critical issue in determining the impact of supersonic aircraft on stratospheric ozone. It has long been held that the first step in the mechanism of aerosol formation is the oxidation of SO2 emitted from the engine by OH in the exhaust plume. We report in situ measurements of OH and HO2 in the exhaust plumes of a supersonic (Air France Concorde) and a subsonic (NASA ER-2) aircraft in the lower stratosphere. These measurements imply that reactions with OH are responsible for oxidizing only a small fraction of SO2 (2%), and thus cannot explain the large number of particles observed in the exhaust wake of the Concorde.

During the 1993 NASA Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE), anomalously low nitric oxide (NO) was found in a distinct sunlit layer located above the mid-latitude tropopause. The presence of a significant amount of reactive nitrogen (NO_y) in the layer implies the systematic removal of NO, which is without precedent in stratospheric in situ observations. Large increases in measured chlorine monoxide (ClO) and the hydroperoxyl radical (HO_2) also were observed in the layer. Heterogeneous reaction rate constants of chlorine nitrate (ClONO_2) with hydrogen chloride (HCl) and H_2O to form nitric acid (HNO_3) on sulfate aerosol are enhanced in the NO removal layer by local increases in H_2O and aerosol surface area. The associated conversion of NO_x (= NO + NO_2) to HNO_3 is the most likely cause of the observed low NO and NO_x/NO_y values and high ClO values.

Extensive in situ measurements of reactive nitrogen (NO y ) and ozone (O 3 ) were made in the lower stratosphere over a broad latitude range (60°N-70°S) during two different seasons (March and October) in 1994. Both NO y and O 3 mixing ratios show a strong latitude dependence, with values increasing toward the poles. The NO y /O 3 ratio reveals a high-gradient region near the tropics that is not well-represented in standard 2-D photochemical transport models. Improving the representation by changing the horizontal eddy-diffusion coefficients near the tropics has important implications for the predicted impacts of aircraft emissions on stratospheric O 3 .

This paper reports measurements of absolute differential cross sections for the direct scattering of oxygen atoms by He, Ne, Ar, Kr, Xe, ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, CO, ${\mathrm{CO}}_{2}$, ${\mathrm{H}}_{2}$O, ${\mathrm{SO}}_{2}$, ${\mathrm{NH}}_{3}$, ${\mathrm{CH}}_{4}$, ${\mathrm{CF}}_{4}$, and ${\mathrm{SF}}_{6}$ targets. The measured cross sections include contributions from all elastic and inelastic processes that result in a fast neutral oxygen atom product. Cross sections are presented for 0.5- and 1.5-keV projectile energies over the laboratory angular range 0.2\ifmmode^\circ\else\textdegree\fi{}--5\ifmmode^\circ\else\textdegree\fi{}. When compared in the center-of-mass reference frame, these cross sections exhibit a high degree of similarity in both amplitude and angular dependence. The cross sections for ${\mathrm{N}}_{2}$, CO, ${\mathrm{CO}}_{2}$, and ${\mathrm{H}}_{2}$O are inverted using a partial-wave analysis to yield empirical interaction potentials, which can then be used to extrapolate the measurements down to lower energies. Using these potentials, cross sections are evaluated at 0.1 keV. \textcopyright{} 1996 The American Physical Society.

Emission indices of reactive gases and particles were determined from measurements in the exhaust plume of a Concorde aircraft cruising at supersonic speeds in the stratosphere. Values for NO x (sum of NO and NO 2 ) agree well with ground-based estimates. Measurements of NO x and HO x indicate a limited role for nitric acid in the plume. The large number of submicrometer particles measured implies efficient conversion of fuel sulfur to sulfuric acid in the engine or at emission. A new fleet of supersonic aircraft with similar particle emissions would significantly increase stratospheric aerosol surface areas and may increase ozone loss above that expected for NO x emissions alone.

A complex three-dimensional (3D) feather-like AlN nanostructure was synthesized by a direct reaction of high-purity Al granules with nitrogen using an arc discharge method. By adjusting the discharge time, a coral-like nanostructure, which evolved from the feather-like nanostructure, has also been observed. The novel 3D feather-like AlN nanostructure has a hierarchical dendritic structure, which means that the angle between the trunk stem and its branch is always about 30° in any part of the structure. The fine branches on the surface of the feather-like nanostructure have shown a uniform fish scale shape, which are about 100 nm long, 10 nm thick and several tens of nanometers in width. An alternate growth model has been proposed to explain the novel nanostructure. The spectrum of the feather-like products shows a strong blue emission band centered at 438 nm (2.84 eV), which indicates their potential application as blue light-emitting diodes.

Rates for large-scale vertical transport of air in the Tropical Tropopause Layer (TTL) were determined using high-resolution, in situ observations of CO2 concentrations in the tropical upper troposphere and lower stratosphere during the NASA Tropical Composition, Cloud and Climate Coupling (TC4) campaign in August 2007. Upward movement of trace gases in the deep tropics was notably slower in TC4 than during the Costa Rica AURA Validation Experiment (CR-AVE), in January 2006. Transport rates in the TTL were combined with in situ measurements of chlorinated and brominated organic compounds from whole air samples to determine chemical loss rates for reactive chemical species, providing empirical vertical profiles for 24-h mean concentrations of hydroxyl radicals (OH) and chlorine atoms in the TTL. The analysis shows that important short-lived species such as CHCl3, CH2Cl2, and CH2Br2 have longer chemical lifetimes than the time for transit of the TTL, implying that these species, which are not included in most models, could readily reach the stratosphere and make significant contributions of chlorine and/or bromine to stratospheric loading.

Measurements and calculations of differential cross sections for direct scattering, single-charge transfer, and double-charge transfer in collisions of 1.5-, 2.0-, 6.0-, and 10.0-keV (He-3)2+ with an He-4 target are reported. The measurements cover laboratory scattering angles below 1.5 deg with an angular resolution of about 0.03 deg. A quantum-mechanical molecular-state representation is employed in the calculations; in the case of single-charge transfer a two-state close-coupling calculation is carried out taking into account electron-translation effects. The theoretical calculations agree well with the experimental results for direct scattering and double-charge transfer. The present calculation identifies the origins of oscillatory structures observed in the differential cross sections.

Measurements of absolute differential cross sections for ${\mathrm{H}}^{+}$-${\mathrm{H}}_{2}$ direct, single-, and double-charge-transfer scattering at 0.5, 1.5, and 5.0 keV are reported at laboratory scattering angles less than 1\ifmmode^\circ\else\textdegree\fi{} with an angular resolution of approximately 0.02\ifmmode^\circ\else\textdegree\fi{}. The cross sections exhibit deep interference oscillations in single-charge-transfer scattering, but no such oscillations are present in direct and double-charge-transfer scattering. Theoretical cross sections derived using the diatoms-in-molecules method to describe the molecular states in a semiclassical molecular-orbital three-state close-coupling model within a semiclassical framework agree satisfactorily with the experimental results.

Absolute differential cross sections for charge-transfer scattering of ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ from molecules are reported over the laboratory angular range 0.02\ifmmode^\circ\else\textdegree\fi{}--1.0\ifmmode^\circ\else\textdegree\fi{}. Cross sections have been determined at 0.5, 1.5, and 5.0 keV for collisions of ${\mathrm{H}}^{+}$ with ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}$, and at 1.5 keV for collisions of ${\mathrm{H}}^{+}$ with CO, ${\mathrm{CO}}_{2}$, NO, and ${\mathrm{CH}}_{4}$, and of ${\mathrm{He}}^{+}$ with ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, CO, and NO. The data exhibit considerable structure over the experimental angular range. Absolute integral cross sections from 0\ifmmode^\circ\else\textdegree\fi{} to 1.0\ifmmode^\circ\else\textdegree\fi{} have been obtained and are compared with the published total cross sections.

Observations of CO2 were made in the upper troposphere and lower stratosphere in the deep tropics in order to determine the patterns of large-scale vertical transport and age of air in the Tropical Tropopause Layer (TTL). Flights aboard the NASA WB-57F aircraft over Central America and adjacent ocean areas took place in January and February, 2004 (Pre-AURA Validation Experiment, Pre-AVE) and 2006 (Costa Rice AVE, CR-AVE), and for the same flight dates of 2006, aboard the Proteus aircraft from the surface to 15 km over Darwin, Australia (Tropical Warm Pool International Cloud Experiment , TWP-ICE). The data demonstrate that the TTL is composed of two layers with distinctive features: (1) the lower TTL, 350–360 K (potential temperature (θ); approximately 12–14 km), is subject to inputs of convective outflows, as indicated by layers of variable CO2 concentrations, with air parcels of zero age distributed throughout the layer; (2) the upper TTL, from θ= ~360 K to ~390 K (14–18 km), ascends slowly and ages uniformly, as shown by a linear decline in CO2 mixing ratio tightly correlated with altitude, associated with increasing age. This division is confirmed by ensemble trajectory analysis. The CO2 concentration at the level of 360 K was 380.0(±0.2) ppmv, indistinguishable from surface site values in the Intertropical Convergence Zone (ITCZ) for the flight dates. Values declined with altitude to 379.2(±0.2) ppmv at 390 K, implying that air in the upper TTL monotonically ages while ascending. In combination with the winter slope of the CO2 seasonal cycle (+10.8±0.4 ppmv/yr), the vertical gradient of 0.78 (±0.09) ppmv gives a mean age of 26(±3) days for the air at 390 K and a mean ascent rate of 1.5(±0.3) mm s−1. The TTL near 360 K in the Southern Hemisphere over Australia is very close in CO2 composition to the TTL in the Northern Hemisphere over Costa Rica, with strong contrasts emerging at lower altitudes (

Sn1−xCoxO2 films have been fabricated to study the local structure of Co dopant and the mediation effects of donor defects (oxygen vacancies and Sn interstitials) on magnetic properties. Compared to as-grown film, the ferromagnetism is evidently enhanced after annealing in vacuum at 400 °C due to the increase in oxygen vacancies. While annealing at higher temperature, the ferromagnetism declines because of the domination of decrease in Sn interstitials over increase in oxygen vacancies in the films. The incorporation of Co dopant as well as the presence of oxygen vacancies and Sn interstitials is verified using x-ray absorption fine structure spectroscopy. The variations in the concentration of defects as a function of annealing temperature are obtained by positron annihilation spectroscopy technique. Additionally, the changes in structure and ferromagnetism after annealing in different atmospheres further demonstrate the crucial roles of oxygen vacancies and Sn interstitials in tuning ferromagnetism.

This paper reports measurements of absolute differential cross sections for electron capture and loss for fast hydrogen atoms incident on H2, N2, O2, Ar, and He. Cross sections have been determined in the 2.0- to 5.0-keV energy range over the laboratory angular range 0.02-2 deg, with an angular, resolution of 0.02 deg. The high angular resolution allows observation of the structure at small angles in some of the cross sections. Comparison of the present results with those of other authors generally shows very good agreement.

Irradiation damage of FeCrCo, AlNiCo, SmCo, and NdFeB permanent magnets was investigated by using γ-ray irradiation. Results of magnetic property measurement show that FeCrCo and NdFeB have more demagnetization than AlNiCo and SmCo. X-ray diffraction analysis shows that γ-ray irradiation leads to the increase of FeCrCo crystal mismatch and decrease of AlNiCo ordering degree. The investigations by positron annihilation spectroscopy technique show that the defects in AlNiCo and SmCo increase after γ-ray irradiation. The defects induced by γ-ray irradiation in NdFeB magnets are not the main source that leads to partial demagnetization. The irradiation resistances of these magnets are discussed in detail considering the thermal stability, coercivity mechanisms, and defect damage.

Absolute differential cross sections for He+He elastic scattering at laboratory angles in the range 0.018/sup 0/--0.5/sup 0/ have been measured for projectile energies of 0.5, 1.5, and 5.0 keV. The experiment employs a position-sensitive detector for determining the angular distribution of scattered particles. The differential cross sections exhibit a transition from classical to quantum behavior within the range of angles studied, and excellent agreement is observed with partial-wave-theory calculations using phase shifts derived from the He-He interaction potentials of Ceperley and Partridge (J. Chem. Phys. 84, 820 (1986)) and Foreman, Rol, and Coffin (J. Chem. Phys. 61, 1658 (1974)).

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.

This paper reports measurements and calculations of absolute differential cross sections for H{sup +}-He charge-transfer and direct scattering. Charge-transfer measurements have been obtained at 5.0 keV laboratory energy over the laboratory angular range 0.02{degree}--1.0{degree}, while direct scattering has been observed at 0.5, 1.5, and 5.0 keV laboratory energy over a closely corresponding angular range. Calculations are reported for 0.5, 1.5, and 5.0 keV charge-transfer and direct scattering. The measured cross sections are in good agreement with those derived from fully quantum-mechanical molecular-orbital close-coupling calculations. Direct scattering cross sections are also found to be in agreement with single-potential calculations using directly summed Jeffreys-Wentzel-Kramers-Brillouin phase shifts derived from proposed H{sup +}-He ground-state interaction potentials. The cross sections exhibit significant structure over the range of angles and energies studied. The measured cross sections have been integrated over the experimental angular range providing absolute integral cross sections for comparison with theoretical results and previously measured total cross sections.

Relative differential cross sections for He-He collisions in the keV-energy range are reported for laboratory scattering angles between 35/sup 0/ and 56/sup 0/. The experiment utilizes two position-sensitive detectors to detect both collision products in coincidence following the collision. A strong periodic variation in the differential cross section with scattering angle is present whenever the collision partners have identical nuclei and is ascribable to well-known interference effects resulting from the indistinguishability of the collision products. Calculations of these differential cross sections considering only the Coulomb interaction between nuclei of the colliding atoms agree well with the experimental data.

This paper reports measurements of absolute differential cross sections for elastic scattering of 0.5-, 1.5-, and 5.0-keV He atoms by Ne, Ar, Kr, and Xe at laboratory scattering angles between 0.05\ifmmode^\circ\else\textdegree\fi{} and 0.5\ifmmode^\circ\else\textdegree\fi{}. Comparisons are made between the measured differential cross sections and those calculated from various model potentials. These comparisons reveal the range of validity of potentials appearing in the literature and provide new information about the lower repulsive walls of the ground-state He\char21{}rare-gas interaction potentials.

Absolute differential cross sections for scattering of 0.5-, 1.5-, and 5.0-keV H and He atoms by H/sub 2/ and N/sub 2/ over the laboratory angular range 0.05/sup 0/--0.5/sup 0/ are reported. Charged collision products are not detected, and no determination is made of the energy loss experienced by the scattered projectile. The measured cross sections therefore include both inelastic and elastic processes. The data are in excellent accord with previous measurements of these processes at larger angles. The data have been integrated over angle to permit comparison with other experimental data.

Measurements of absolute differential cross sections for direct and charge-transfer scattering of ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ by the rare gases have been made. Direct scattering cross sections are reported at 1.5 keV for collisions of ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ with Ne, Ar, Kr, and Xe over the laboratory angular range 0.03\ifmmode^\circ\else\textdegree\fi{}--1.0\ifmmode^\circ\else\textdegree\fi{}. Charge-transfer cross sections are reported for the laboratory scattering angles below 1.0\ifmmode^\circ\else\textdegree\fi{} for ${\mathrm{H}}^{+}$-Ar, Kr at 0.5, 1.5, and 5.0 keV, for ${\mathrm{H}}^{+}$-Xe at 5.0 keV, and for ${\mathrm{He}}^{+}$-Ne at 1.5 keV. The data exhibit a wealth of structure over the experimental angular range, and cross sections have been integrated over angle to provide absolute integral cross sections.

Absolute differential cross sections are reported for collisions between 0.5, 1.5, and 5.0-keV-energy H atoms and He, Ne, Ar, Kr, and Xe over the laboratory-frame angular range 0.018\ifmmode^\circ\else\textdegree\fi{}--0.5\ifmmode^\circ\else\textdegree\fi{}. The scattered neutral particles are detected, and the measured cross sections include both elastic and inelastic events. The H-He results are in excellent accord with previous measurements at larger angles. Empirical interaction potential-energy curves have been extracted from the data for all collisions studied.