Robert E. Sievers

Measurements of aromatic hydrocarbon ratios and NOx concentrations in the rural troposphere: Observation of air mass photochemical aging and NOx removal

Abstract Measurements of the aromatic hydrocarbons (benzene, toluene, ethylbenzene and ortho(o)-xylene) at Niwot Ridge, Colorado have shown distinct correlations between the ratios of the concentrations of these compounds and the degree of direct urban influence. The major atmospheric removal mechanism of aromatic hydrocarbons is reaction with the hydroxyl radical, OH. This allows the decrease in the ratios of aromatic hydrocarbon concentrations to be related to the transport time and average OH number density within an air mass, if assumptions are made concerning background sources of aromatic hydrocarbons. Measured ratios of aromatic compounds at this site, along with ratios reported for several cities in the western United States, and estimates of transport times from these cities were used to calculate temporally and spatially averaged OH number densities. Hydroxyl radical number density estimates using toluene-, ethylbenzene-, and o-xylene-to-benzene ratios, were 1.2 ± 0.6 × 106, 1.0 ±0.8 × 106 and 0.48 ± 0.8 × 106 molecules cm−3, respectively. Considering the uncertainties in the assumptions used in the above estimates, we obtain a diurnal-average upper limit of 2.4 × 106 molecules cm−3. The correlations between measured ratios are found to yield slopes consistent with those predicted by experimental OH rate constants for benzene, toluene and ethylbenzene, and approximately a factor of two different in the case of benzene, toluene and o-xylene. The ratio of NOx: benzene was found to yield no correlation with toluene: benzene ratio for periods of westerly flow, but was well correlated with toluene: benzene ratio during periods of direct urban impact on the site (upslope easterly winds). The correlation of these ratios in urban plume air masses was consistent with NO2 + OH + M being the major daytime removal mechanism of NOx in the summertime.

Vapor Deposition of Metals by Hydrogen Reduction of Metal Chelates

Thin film deposits of Cu, Ni, and Rh were obtained by hydrogen reduction of , , , and from the gas phase (tfa = trifluoroacetylacetonate anion; hfa = hexafluoroacetylacetonate anion). The chelates are well suited for gas plating purposes by virtue of their high volatility and ease of reduction by hydrogen. The deposition process can be conducted at atmospheric pressure and at temperatures as low as 250°C. The process is potentially cyclic, free chelating agent being regenerated by the reduction reaction.

SUBMICRON-SIZED SPHERICAL YTTRIUM OXIDE BASED PHOSPHORS PREPARED BY SUPERCRITICAL CO2-ASSISTED AEROSOLIZATION AND PYROLYSIS

The synthesis of Eu(III)- and Tb(III)-doped yttrium oxide phosphor powders by supercritical CO2-assisted aerosolization and pyrolysis (at 1010 °C) from aqueous solutions of Y(NO3)3, Eu(NO3)3, and Tb(NO3)3 is presented. Dense, submicron aerosols are formed by contacting aqueous solutions of the precursor metal nitrates with supercritical CO2 at 1500 psi, and decompressing the mixture through a restrictor nozzle into a heated tube. X-ray diffraction data indicate that the powders are crystalline, and consist of a single phase. Scanning electron microscope shows that they are spherical in morphology and less than 1 μm in size with average diameters of ∼0.2 μm. The cathodoluminescence intensity of the Y1.91Eu0.09O3 powders, annealed at 1200 °C for 1 h, is more than twice greater than that of the industrial standard (P56, 3–10 μm in diameter) phosphor. The phosphors synthesized by this method are promising candidates for use in high-resolution low-voltage flat panel displays.

Monoterpene hydrocarbons in the nighttime troposphere.

Monoterpene hydrocarbons were measured during the night at a rural site in the Rocky Mountains. The compounds positively identified and quantified were ..cap alpha..-pinene, camphene, ..beta..-pinene, ..delta../sup 3/-carene, and d-limonene. The average sum of the mixing ratios of the five compounds measured during the nighttime between July and Oct., 1982, was 0.63 ppb (volume), which was about twice the corresponding daytime average sum. No significant difference was observed between day and night in the relative concentrations of the individual monoterpenes. Increased atmospheric stability, with attendant reduced mixing and dilution during the night, was found to contribute to the large nighttime vs. daytime monoterpene mixing ratios. Nighttime atmospheric stability was also responsible for the observation of ozone diminution and a corresponding inverse relationship between monoterpene and ozone mixing ratios. The results indicate that, at this site, transport rather than chemistry determines the concentrations of the monoterpenes. The ultimate fate of the monoterpenes is chemical reaction with O/sub 3/, OH, or NO/sub 3/. Because of the differences in rate constants of reactions between the various monoterpenes and the above species, chemical reaction should cause systematic changes in relative concentrations of monoterpenes, which are characteristic of the reactant species involved.

Microdetermination of nitrates and nitrites in saliva, blood, water, and suspended particulates in air by gas chromatography

A generally applicable method for the analysis of nitrates and nitrites has been used for a wide variety of samples, including human saliva, blood, drinking water, and airborne particulates. Aqueous nitrate ion is first converted to nitrobenzene by reaction with benzene (or another aromatic reactant) in the presence of a catalyst. The nitrobenzene is then quantitated by electron capture gas chromatography (GC-ECD). Nitrite ion and gaseous oxides of nitrogen can be determined also if such samples are treated appropriately prior to CG-ECD analysis. Other reactants such as 1,3,5-trimethoxybenzene can also be used in the place of benzene. The high sensitivity of ECD allows the quantitation of as little as 0.1 ppm (w/w) nitrate in a single drop of saliva or blood.

Deposition of palladium films by a novel supercritical fluid transport-chemical deposition process

Abstract Palladium was pyrolytically deposited by a supercritical fluid transport-chemical deposition method using the metal β-diketonate complex bis-(2,2,7-trimethyl-3,5-octanedionato)palladium(II). Deposition at a rate of 95 nm/min occurred at a substrate temperature of 740 °C. X-ray diffraction and electron microprobe analyses of the reflective films that were deposited on fused silica substrates showed that they contained polycrystalline palladium. The films were electrically conductive, but conductivity was substantially lower than that for bulk palladium. X-ray diffraction of the films deposited on (100) Si substrates showed that palladium silicide was formed.

Highly permeable open-pore polyurethane columns for liquid chromatography

Novel highly permeable polyurethane chromatogrphic columns have been prepared by thein Situ polymerization of toluene-carbon tetrachloride solutions of a polyol and an isocyanate which have been drawn into narrow-bore glass tubing. The agglomerated spherical polyurethane particles are bonded to each other in a rigid monolithic structure and are very homogeneous: depending on plymerization conditions, particles 1 to 10 μm in diameter can be prepared. Even though the columns are filled with very small particles, they show extremely high permeabilities. For example, 1-m 2.3-mm-I.D. columns exhibit less thant 100 p.s.i. inlet pressure at a 1.0 ml flow-rate with most solvents. Owing to the high capacity of the plyurethane columns, high-speedc analytical separations have been performed at 3 p.s.i. inlet pressure and preparative-scale separations have been performed on milligram quantities in less than 1 h.

Thermogravimetric studies of metal β-diketonates☆

Abstract Thermogravimetric analysis (TGA) is applied to the rapid determination of the relative volatilities of various metal β-diketonate chelates. Differences are seen in the volatility of a series of thermally stable tris (2,2,6,6-tetramethyl-3,5-heptanedionato) rare earth chelates. The trend in volatility of the rare earth chelates is related to the size of the trivalent rare earth ion and is independent of chelate mass. The order of increasing volatility as seen from the thermograms of the volatile rare earth chelates parallels the order of increasing ease of elution of these chelates from non-polar gas chromatographic liquid partioning phases. Some of the chelates are considerably more volatile than alkane hydrocarbons of considerably lower carbon number. Volatilities of metal β-diketonates of Cr(III), Fe(III), Rh(III), Al(III), Na(I), Zr(IV), Sc(III), Y(III), and the trivalent lanthanides are compared. Differences in the volatilities of metal chelates, arising from substitution in the chelate ligand, are illustrated for metal chelate derivatives of various β-diketone ligands.

Successful respiratory immunization with dry powder live-attenuated measles virus vaccine in rhesus macaques

Measles remains an important cause of childhood mortality worldwide. Sustained high vaccination coverage is the key to preventing measles deaths. Because measles vaccine is delivered by injection, hurdles to high coverage include the need for trained medical personnel and a cold chain, waste of vaccine in multidose vials and risks associated with needle use and disposal. Respiratory vaccine delivery could lower these barriers and facilitate sustained high coverage. We developed a novel single unit dose, dry powder live-attenuated measles vaccine (MVDP) for respiratory delivery without reconstitution. We tested the immunogenicity and protective efficacy in rhesus macaques of one dose of MVDP delivered either with a mask or directly intranasal with two dry powder inhalers, PuffHaler and BD Solovent. MVDP induced robust measles virus (MeV)-specific humoral and T-cell responses, without adverse effects, which completely protected the macaques from infection with wild-type MeV more than one year later. Respiratory delivery of MVDP was safe and effective and could aid in measles control.

Stabilizing Formulations for Inhalable Powders of Live-Attenuated Measles Virus Vaccine

Carbon dioxide Assisted Nebulization with a Bubble Dryer((R)) (CAN-BD) processing allows particles to be made in the 3-5 mum size range, which is desirable for lung delivery, without destroying biological activity. In response to the Grand Challenge in Global Health Initiative #3, we have been developing an inhalable needle-free live-attenuated measles virus vaccine for use in developing countries. Measles was chosen because it is the number one vaccine preventable killer of children worldwide. Powders were processed by CAN-BD, where a solution containing excipients and live-attenuated measles virus in water was mixed intimately with supercritical or near superctitical carbon dioxide to form an emulsion. The emulsion was expanded to atmospheric pressure through a flow restrictor. The resulting plume was dried by heated nitrogen and the powders collected on a filter at the bottom of the drying chamber. Powders were analyzed using varying techniques including X-ray diffraction, scanning electron microscopy, Andersen cascade impaction, differential scanning calorimetery, Karl Fischer titration, and viral plaque assay. CAN-BD has been used to produce powders of live-attenuated measles virus vaccine with characteristics desirable for lung delivery. The powders retain viral activity through forming and drying the microparticles by CAN-BD, and have passed the WHO stability test for 1 week at 37 degrees C. The powders have an amorphous character and a glass transition temperature of around 60 degrees C. Lyophilization, the present standard commercial method of processing measles vaccine makes solids with a water content of less than 1%. By substituting myo-inositol for sorbitol and using the CAN-BD drying technique the water content can be lowered to 0.5%. The most successful formulations to date have been based conceptually on the current lyophilized formulation, but with modifications to the type and amounts of sugar. Of current interest are formulations containing myo-inositol, as they retain high viral activity and have low initial water content.