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PubMed2006

Performances under representative pressure and temperature conditions of the gas chromatography-mass spectrometry space experiment to investigate Titan's atmospheric composition.

In the frame of the calibration of the aerosol collector and pyrolyser, and gas chromatography-mass spectrometry experiments of the Huygens probe arrived at Titan, systematic experimental studies were led to estimate the influence of the operating conditions on the analyses that should have been achieved in the Titan's atmosphere. The primary objective of this study was to estimate the influence of operating conditions variations induced by (i) instrumental modifications made shortly before the probe launch which can have changed the operating pressures; (ii) the change of the probe environmental conditions (pressure, temperature) during its descent in the atmosphere; (iii) a possible deviation of pressure and temperature regulations from their nominal values because of the long journey of the instrument in space, or of other external events. The secondary objective of this work was to create an analytical database that can be used as a reference to treat the chromatograms obtained in situ, and help to identify chromatographically the analyzed species, complementary to mass spectrometry. Beyond the application to a specific instrument, this work was also useful to experimentally estimate the fundamental evolution of the separation as a function of the changes of operating conditions with time. The obtained results show (i) the significant influence of inlet and outlet pressure variation on the time of analysis, but not on the separation power. It thus enables to significantly shorten the analysis duration, and thus to analyze more compounds within the fixed time of analysis of the instrument; (ii) the significant influence of temperature on the retention. In this frame, the enthalpies of exchange between the gas phase and the stationary phase of the species were determined to be used to retrieve the analyzed species in case of deviation of the operating temperature; (iii) that the possible aging of the columns does not have influence on the columns efficiency and separation power; (iv) the analytical capabilities of the gas chromatography-mass spectrometry experiment within operating conditions representative of those encountered in situ. Finally, in spite of possible operating condition changes, it is shown that results coming from the gas chromatograph-mass spectrometer experiment, which are currently under analysis, could bring important information on the Titan's atmosphere and its history.

Atmosphere↗
PubMed2006

Investigation of mercury exchange between forest canopy vegetation and the atmosphere using a new dynamic chamber.

This paper presents the design of a dynamic chamber system that allows full transmission of PAR and UV radiation and permits enclosed intact foliage to maintain normal physiological function while Hg(0) flux rates are quantified in the field. Black spruce and jack pine foliage both emitted and absorbed Hg(0), exhibiting compensation points near atmospheric Hg(0) concentrations of approximately 2-3 ng m(-3). Using enriched stable Hg isotope spikes, patterns of spike Hg(ll) retention on foliage were investigated. Hg(0) evasion rates from foliage were simultaneously measured using the chamber to determine if the decline of foliar spike Hg(II) concentrations over time could be explained by the photoreduction and re-emission of spike Hg to the atmosphere. This mass balance approach suggested that spike Hg(0) fluxes alone could not account for the measured decrease in spike Hg(II) on foliage following application, implying that eitherthe chamber underestimates the true photoreduction of Hg(ll) to Hg(0) on foliage, or other mechanisms of Hg(II) loss from foliage, such as cuticle weathering, are in effect. The radiation spectrum responsible for the photoreduction of newly deposited Hg(II) on foliage was also investigated. Our spike experiments suggest that some of the Hg(ll) in wet deposition retained by the forest canopy may be rapidly photoreduced to Hg(0) and re-emitted back to the atmosphere, while another portion may be retained by foliage at the end of the growing season, with some being deposited in litterfall. This finding has implications for the estimation of Hg dry deposition based on throughfall and litterfall fluxes.

Atmosphere↗
PubMed1998

Potential applications of differential permeability membranes in the control of gas composition in closed circuit atmospheres.

Long hyperbaric exposures of humans, at pressures in excess of 2.5 atmospheres, require that the oxygen concentration of the breathing gas be maintained at levels less than atmospheric air, in order to prevent pulmonary oxygen toxicity. Carbon dioxide produced by humans must be removed from the breathing gas of closed environments. Differential permeability gas separation devices can be used to reduce the concentrations of carbon dioxide and oxygen in recirculating nitrogen/oxygen atmospheres. The application of these devices can eliminate the requirement for nitrogen to dilute oxygen, and reduce, or eliminate, the requirement for carbon dioxide absorbents. The use of differential permeability gas separation devices for the production of nitrogen/oxygen breathing gas mixtures for divers, using air as a source gas, can produce mixtures with unacceptably high levels of carbon dioxide.

Air Conditioning↗
PubMedDate not supplied

[The anodyne action of narcotic analgesics and clofelin under increased atmospheric pressure].

Rat experiments have revealed that gradual increases in atmospheric pressure up to 1.1 MPa progressively alters the vocalization threshold in electrical stimulation of the tail root. Substitution of air for heliox (79.1% helium and 20.9% oxygen) leads to attenuation of the analgesic effect of hyperbarism. It is postulated that hyperbaric analgesia is due mainly to the elevated partial pressure of nitrogen. Morphine and promedol in doses of 2.5 mg/kg and clofeline in a dose of 0.1 mg failed to change analgesic effects when atmospheric pressure was increased up to 0.7 and 1.1 MPa. The analgesic effect of morphine and promedol in doses of 5 mg/kg and buprenorphine in a dose of 0.035 mg/kg under similar conditions increased during the whole period of isopression, while that of clofeline in a dose of 0.5 mg/kg increased only in the first few minutes of isopression. The analgesic action of morphoeceptine in a dose of 5 mg/kg decreased during isopression. The possible mechanisms of hyperbaric analgesia and the specific features of the analgesic action of different drugs at elevated atmospheric pressure are discussed.

Analgesics, Opioid↗
PubMedDate not supplied

Analysis of voltammetric data for the evaluation of seasonal changes of the Ni, Cd, Pb and Cu content in atmospheric particulate PM2.5.

In this paper, the preliminary results of a study on concentration of heavy metals in PM2.5 (atmospheric particles with aerodynamic diameter less than 2.5 microm) fractions of atmospheric particulate matter, sampled in Milan, are presented. This work aims to develop an electroanalytical method to analyse Pb, Cu, Cd and Ni in PM2.5 and to investigate seasonal and weekly trends in the amount of PM2.5 and its composition for considered metals. The samples have been selected within the seasons ranging from September 2002 to November 2003 so that they represent the possible seasonal changes; the samples within this period have been chosen in order to have data relevant to both working days and holidays. The determination of Cd, Pb and Cu has been carried out by Differential Pulse Anodic Stripping Voltammetry, whereas the concentration of Ni has been determined by Differential Pulse Adsorptive Cathodic Stripping Voltammetry. The concentrations of the metals in the sampled atmosphere and in the PM2.5 have been evaluated; through ANOVA possible seasonal or weekly variations in the above cited concentrations have been investigated.

Air Pollutants↗
PubMed2005

Atmospheric aerosols: composition, transformation, climate and health effects.

Aerosols are of central importance for atmospheric chemistry and physics, the biosphere, climate, and public health. The airborne solid and liquid particles in the nanometer to micrometer size range influence the energy balance of the Earth, the hydrological cycle, atmospheric circulation, and the abundance of greenhouse and reactive trace gases. Moreover, they play important roles in the reproduction of biological organisms and can cause or enhance diseases. The primary parameters that determine the environmental and health effects of aerosol particles are their concentration, size, structure, and chemical composition. These parameters, however, are spatially and temporally highly variable. The quantification and identification of biological particles and carbonaceous components of fine particulate matter in the air (organic compounds and black or elemental carbon, respectively) represent demanding analytical challenges. This Review outlines the current state of knowledge, major open questions, and research perspectives on the properties and interactions of atmospheric aerosols and their effects on climate and human health.

Aerosols↗
PubMed2004

From earth's primitive atmosphere to chiral peptides--the origin of precursors for life.

To re-enact the long way to the origin of life with today's chemical methods, many steps have to be investigated in the light of a primordial scenario deduced from geochemical research. After the formation of our planet and its atmosphere, prebiotic chemical evolution started its course with the formation of the first building blocks for the formation of biomolecules. In the case of proteins, those building blocks were amino acids that had to be formed in the primitive atmosphere, and then had to react to peptides and proteins as the main pillar of first life. In this paper, we describe the processes in the primordial atmosphere according to contemporary geochemical knowledge leading to the synthesis of amino acids until the formation of homochiral peptides, and, thus, show a plausible pathway towards the origin of life.

Amino Acids↗
PubMed2004

Atmospheric organic aerosol production by heterogeneous acid-catalyzed reactions.

Exploratory evidence from our laboratories shows that acidic surfaces on atmospheric aerosols lead to very real and potentially multifold increases in secondary organic aerosol (SOA) mass and build-up of stabilized nonvolatile organic matter as particles age. One possible explanation for these heterogeneous processes are the acid-catalyzed (e.g., H2SO4 and HNO3) reactions of atmospheric multifunctional organic species (e.g., multifunctional carbonyl compounds) that are accommodated onto the particle phase from the gas phase. Volatile organic hydrocarbons (VOCs) from biogenic sources (e.g., terpenoids) and anthropogenic sources (aromatics) are significant precursors for multifunctional organic species. The sulfur content of fossil fuels, which is released into the atmosphere as SO2, results in the formation of secondary inorganic acidic aerosols or indigenous acidic soot particles (e.g., diesel soot). The predominance of SOAs contributing to PM2.5 (particulate matter, that is, 2.5 microm or smaller than 2.5 microm), and the prevalence of sulfur in fossil fuels suggests that interactions between these sources could be considerable. This study outlines a systematic approach for exploring the fundamental chemistry of these particle-phase heterogeneous reactions. If acid-catalyzed heterogeneous reactions of SOA products are included in next-generation models, the predicted SOA formation will be much greater and have a much larger impact on climate-forcing effects than we now predict. The combined study of both organic and inorganic acids will also enable greater understanding of the adverse health effects in biological pulmonary organs exposed to particles.

Aerosols↗
PubMed2004

N2O influence on isotopic measurements of atmospheric CO2.

In spite of extensive efforts, even the most experienced laboratories dealing with isotopic measurements of atmospheric CO2 still suffer from poor inter-laboratory consistency. One of the complicating factors of these isotope measurements is the presence of N2O, giving rise to mass overlap in the isotope ratio mass spectrometer (IRMS). The aim of the experiment reported here has been twofold: first, the re-establishment of the correction for 'mechanical' interference of N2O in the IRMS, along with its variability and drift, and the best way to quantitatively determine the correction factors. Second, an investigation into secondary effects, i.e. the influence of N2O admitted with the CO2 sample on the "cross contamination" between sample and (pure CO2) working gas. To make the suspected effects better detectable, isotopically enriched CO2 gas with different concentrations of N2O has been measured for the first time. No evidence of secondary effects was observed, from which we conclude that N2O is not a major player in the inter-laboratory consistency problems. Still, we also found that the determination of the 'mechanical' N2O correction needs to be very carefully determined for each individual IRMS, and should be periodically re-determined. We show that the determination of the correction should be performed using CO2/N2O mixtures with concentration ratios around that of the atmosphere, as the extrapolation from pure gas end member behaviour will give erroneous results due to non-linearities. For our IRMS, a VG SIRA series II, we find a correction of 0.23 per thousand for delta45CO2 and 0.30 per thousand for delta46CO2 of atmospheric samples, (with 0.85 per thousand mixing ratio). This implies that the relative ionisation efficiency (E) value associated with this machine is 0.75.

Atmosphere↗
PubMed2004

Functionalized nanoparticles for liquid atmospheric pressure matrix-assisted laser desorption/ionization peptide analysis.

Nanoparticles for the extraction of peptides and subsequent analysis using atmospheric pressure matrix-assisted laser desorption/ionization (APMALDI) have been evaluated. The atmospheric pressure source allows for particles to be directly introduced in the liquid matrix, minimizing sample loss and analysis time. Described in this work are two sample preparation procedures for liquid APMALDI analysis: a C18 functionalized silica nanoparticle for hydrophobic extractions, and an aptamer functionalized magnetite core nanoparticle for rapid, affinity extractions. The C18 particles provide a non-selective support for rapid profiling applications, while the aptamer particles are directed towards reducing the complexity in biological samples. The aptamer functionalized particles provide a more selective analyte-nanoparticle interaction whereby the tertiary structure of the analyte becomes more critical to the extraction. In both cases, the liquid APMALDI matrix provides a support for ionization, and acts as the releasing agent for the analyte-particle interaction. Additionally, analyte enrichment was possible due to the large surface-to-volume ratio of the particles. The experiments conducted with functionalized nanoparticles, in an atmospheric pressure liquid matrix, present a basis for further methodologies and utilities of silica nanoparticles to be developed.

Adsorption↗
PubMed2005

Atmospheric-pressure laser ionization: a novel ionization method for liquid chromatography/mass spectrometry.

We report on the development of a new laser-ionization (LI) source operating at atmospheric pressure (AP) for liquid chromatography/mass spectrometry (LC/MS) applications. APLI is introduced as a powerful addition to existing AP ionization techniques, in particular atmospheric-pressure chemical ionization (APCI), electrospray ionization (ESI), and atmospheric pressure photoionization (APPI). Replacing the one-step VUV approach in APPI with step-wise two-photon ionization strongly enhances the selectivity of the ionization process. Furthermore, the photon flux during an ionization event is drastically increased over that of APPI, leading to very low detection limits. In addition, the APLI mechanism generally operates primarily directly on the analyte. This allows for very efficient ionization even of non-polar compounds such as polycyclic aromatic hydrocarbons (PAHs). The APLI source was characterized with a MicroMass Q-Tof Ultima II analyzer. Both the effluent of an HPLC column containing a number of PAHs (benzo[a]pyrene, fluoranthene, anthracene, fluorene) and samples from direct syringe injection were analyzed with respect to selectivity and sensitivity of the overall system. The liquid phase was vaporized by a conventional APCI inlet (AP probe) with the corona needle removed. Ionization was performed through selective resonance-enhanced multi-photon ionization schemes using a high-repetition-rate fixed-frequency excimer laser operating at 248 nm. Detection limits well within the low-fmol regime are readily obtained for various aromatic hydrocarbons that exhibit long-lived electronic states at the energy level of the first photon. Only molecular ions are generated at the low laser fluxes employed ( approximately 1 MW/cm(2)). The design and performance of the laser-ionization source are presented along with results of the analysis of aromatic hydrocarbons.

Atmospheric Pressure↗
PubMed2005

An automated system for stable isotope and concentration analyses of CO2 from small atmospheric samples.

We have developed an automated, continuous-flow isotope ratio mass spectrometry (CF-IRMS) system for the analysis of delta(13)C, delta(18)O, and CO(2) concentration (micromol mol(-1)) ([CO(2)]) from 2 mL of atmospheric air. Two replicate 1 mL aliquots of atmospheric air are sequentially sampled from fifteen 100 mL flasks. The atmospheric sample is inserted into a helium stream and sent through a gas chromatograph for separation of the gases and subsequent IRMS analysis. Two delta(13)C and delta(18)O standards and five [CO(2)] standards are run with each set of fifteen samples. We obtained a precision of 0.06 per thousand, 0.11 per thousand, and 0.48 micromol mol(-1) for delta(13)C, delta(18)O, and [CO(2)], respectively, by analyzing fifty 100 mL samples filled from five cylinders with a [CO(2)] range of 275 micromol mol(-1). Accuracy was determined by comparison with established methods (dual-inlet IRMS, and nondispersive infrared gas analysis) and found to have a mean offset of 0.00 per thousand, -0.09 per thousand, and -0.26 micromol mol(-1) for delta(13)C and delta(18)O, and [CO(2)], respectively.

Air Pollutants↗
PubMed2005

Vertical gradients of delta15N and delta18O in soil atmospheric N2O--temporal dynamics in a sandy soil.

The greenhouse gas nitrous oxide (N(2)O) can be both formed and consumed by microbial processes in the soil. As these processes fractionate strongly in favour of (14)N and (16)O, delta(15)N and delta(18)O gradients of N(2)O in the soil profile may elucidate patterns of N(2)O formation, consumption or emission to the atmosphere. We present the first in situ data of such gradients over time for a mesic typic Haplaquod seeded with potatoes (Solanum tuberosum L.). On two adjacent fields in 2002 and 2003, topsoil N(2)O fluxes were measured and the soil atmosphere was regularly sampled for N(2)O concentrations, delta(15)N and delta(18)O signatures of N(2)O at depths of 18, 48 and 90 cm during approximately 400 days. During the entire sampling period, the N(2)O concentrations were the highest and the delta(15)N signatures the lowest in the subsoil (48 or 90 cm depth) as compared with the topsoil, indicating production of N(2)O in the subsoil. For delta(15)N, differences greater than 30 per thousand between topsoil and subsoil on the same date were regularly observed. The highest N(2)O concentration of 100385 microL m(-3) at 90 cm depth on 1 July 2003, was preceded by the lowest delta(15)N value of -43.5 per thousand one week earlier. This was followed by a 150-day general decrease of N(2)O concentrations at 90 cm depth to 1723 microL m(-3) and a simultaneous enrichment of delta(15)N to +7.1 per thousand, mostly without a significant topsoil flux. There was a negative logarithmic relationship between N(2)O concentration at 90 cm depth and its delta(15)N signature. This relationship indicated a delta(15)N signature of -40 to -45 per thousand during the production of N(2)O in the subsoil, and a subsequent enrichment during the consumption of N(2)O. We conclude that the isotopic signature of the N(2)O topsoil flux is the result of various processes of consumption and production at different depths in the soil profile. It is therefore not a reliable estimator for the overall delta(15)N signature of N(2)O in the soil atmosphere, nor for indirect losses of N(2)O to the environment. Therefore, these findings will pose a further challenge to ongoing efforts to draw up a global isotopic budget for N(2)O.

Atmosphere↗
PubMed2006

Atmospheric pressure ion/molecule reactions for the selective detection of nitroaromatic explosives using acetonitrile and air as reagents.

Acetonitrile vapor and air are useful reagents for the selective detection of nitroaromatic compounds using atmospheric pressure ion/molecule reactions. Reagent ions CH2CN- and CN- generated from acetonitrile, and O-*, OH- and OOH- produced from the oxygen in air, react with vapor-phase and condensed-phase nitroaromatics in the course of atmospheric pressure chemical ionization (APCI) and desorption atmospheric pressure chemical ionization (DAPCI), respectively. The homogeneous and the heterogeneous phase reactions both lead to the formation of the same anionic adducts. These adducts have characteristic fragmentation patterns upon collisional activation, which makes these two reagents valuable for the selective detection of particular nitroaromatics, including explosives present as components of complex mixtures. Complementary information is available from the two reagents because their different chemistry facilitates analyte identification. DAPCI is demonstrated to be a useful ambient detection method for nitroaromatic explosives absorbed on surfaces.

Acetonitriles↗
PubMed2002

Atmospheric pressure laser desorption/ionization on porous silicon.

A recently developed commercial atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) source (MassTech, Inc.) was modified to adopt commercially available DIOS plates (Mass Consortium Corp.) for the studies of laser desorption from the surface of porous silicon under atmospheric pressure conditions. The feasibility of atmospheric pressure laser desorption/ionization from the surface of porous silicon (AP-DIOS) was demonstrated. The advantages of this new AP-DIOS technique include reasonably good sensitivity (subpicomole range for standard peptide mixtures), simplicity of sample preparation, uniformity of target spots and the absence of matrix peaks in the spectra. The AP-DIOS source was interfaced with a commercial ion trap (LCQ Classic, Thermo Finnigan) which additionally provides a unique MS(n) capability. The AP-DIOS spectrum of 250 fmol of unseparated tryptic digest of bovine serum albumin (BSA) was compared with that of AP-MALDI for the same compound. AP-DIOS offers significantly better coverage for the digest components in the mass range 200-1000 Da. The combined data of both techniques enabled us to nearly double the number of matched peaks in BSA digest analysis compared with AP-DIOS or AP-MALDI analysis separately.

Angiotensins↗
PubMed2001

Pure atmospheric pressure promotes an expression of osteopontin in human aortic smooth muscle cells.

Although the types of pathophysiological stimulation that initiate an overexpression of OPN have yet to be determined, we hypothesized that mechanical stress is one of the candidates which initiates OPN expression in vascular smooth muscle cells. Cell proliferation assay indicated that a pure atmospheric pressure of 160 mmHg activated cell proliferation by 11% in human aortic smooth muscle cells (HASMC) compared to nonpressurized controls. Immunoblot analysis probed with an anti-OPN antibody demonstrated a 50% increase in OPN. Dual-luciferase reporter assay demonstrated that OPN promoter, corresponding to the -771 through -1 region of OPN gene, was highly responsive to pure atmospheric pressure by ten times that of the control. From these observations, we concluded that pure atmospheric pressure directly promotes an expression of OPN in HASMC, with these results also suggesting that high blood pressure-mediated mechanical compression is involved in the process of atherosclerosis and remodeling via OPN expression in HASMC.

Animals↗
PubMed1993

Coupled atmosphere-ocean models of Titan's past.

We have developed a coupled atmosphere and ocean model of Titan's surface. The atmospheric model is a 1-D spectrally-resolved radiative-convective model. The ocean thermodynamics are based upon solution theory. The ocean, initially composed of CH4, becomes progressively enriched in ethane over time. The partial pressures of N2 and CH4 in the atmosphere are dependent on the ocean temperature and composition. We find that the resulting system is stable against a runaway greenhouse. Accounting for the decreased solar luminosity, we find that Titan's surface temperature was about 20 K colder 4 Gyr ago. Without an ocean, but only small CH4 lakes, the temperature change is 12 K. In both cases we find that the surface of Titan may have been ice covered about 3 Gyr ago. In the lakes case condensation of N2 provides the ice, whereas in the ocean case the ocean freezes. The dominant factor influencing the evolution of Titan's surface temperature is the change in the solar constant--amplified, if an ocean is present, by the temperature dependence of the solubility of N2. Accretional heating can dramatically alter the surface temperature; a surface thermal flux of 500 erg cm-2 sec-1, representative of small levels of accretional heating, results in a approximately 20 K change in surface temperatures.

Astronomical Phenomena↗
PubMed1994

A coupled soil-atmosphere model of H2O2 on Mars.

The Viking Gas Chromatograph Mass Spectrometer failed to detect organic compounds on Mars, and both the Viking Labeled Release and the Viking Gas Exchange experiments indicated a reactive soil surface. These results have led to the widespread belief that there are oxidants in the martian soil. Since H2O2 is produced by photochemical processes in the atmosphere of Mars, and has been shown in the laboratory to reproduce closely the Viking LR results, it is a likely candidate for a martian soil oxidant. Here, we report on the results of a coupled soil/atmosphere transport model for H2O2 on Mars. Upon diffusing into the soil, its concentration is determined by the extent to which it is adsorbed and by the rate at which it is catalytically destroyed. An analytical model for calculating the distribution of H2O2 in the martian atmosphere and soil is developed. The concentration of H2O2 in the soil is shown to go to zero at a finite depth, a consequence of the nonlinear soil diffusion equation. The model is parameterized in terms of an unknown quantity, the lifetime of H2O2 against heterogeneous catalytic destruction in the soil. Calculated concentrations are compared with a H2O2 concentration of 30 nmoles/cm3, inferred from the Viking Labeled Release experiment. A significant result of this model is that for a wide range of H2O2 lifetimes (up to 10(5) years), the extinction depth was found to be less than 3 m. The maximum possible concentration in the top 4 cm is calculated to be approximately 240 nmoles/cm3, achieved with lifetimes of greater than 1000 years. Concentrations higher than 30 nmoles/cm3 require lifetimes of greater than 4.3 terrestrial years. For a wide range of H2O2 lifetimes, it was found that the atmospheric concentration is only weakly coupled with soil loss processes. Losses to the soil become significant only when lifetimes are less than a few hours. If there are depths below which H2O2 is not transported, it is plausible that organic compounds, protected from an oxidizing environment, may still exist. They would have been deposited by meteors, or be the organic remains of past life.

Atmosphere↗