Cm6 Molecule Research Articles

Speciated Monitoring of Gas-Phase Organic Peroxy Radicals by Chemical Ionization Mass Spectrometry: Cross-Reactions between CH3O2, CH3(CO)O2, (CH3)3CO2, and c-C6H11O2.

Organic peroxy radicals ("RO2", with R organic) are key intermediates in most oxygen-rich systems, where organic compounds are oxidized (natural environment, flames, combustion engines, living organisms, etc). But, until recently, techniques able to monitor simultaneously and distinguish between RO2 species ("speciated" detection) have been scarce, which has limited the understanding of complex systems containing these radicals. Mass spectrometry using proton transfer ionization has been shown previously to detect individual gas-phase RO2 separately. In this work, we illustrate its ability to speciate and monitor several RO2 simultaneously by investigating reactions involving CH3O2, CH3C(O)O2, c-C6H11O2, and (CH3)3CO2. The detection sensitivity of each of these radicals was estimated by titration with NO to between 50 and 1000 Hz/ppb, with a factor from 3 to 5 of uncertainties, mostly due to the uncertainties in knowing the amounts of added NO. With this, the RO2 concentration in the reactor was estimated between 1 × 1010 and 1 × 1012 molecules cm-3. When adding a second radical species to the reactor, the kinetics of the cross-reaction could be studied directly from the decay of the first radical. The time-evolution of two and sometimes three different RO2 was followed simultaneously, as the CH3O2 produced in further reaction steps was also detected in some systems. The rate coefficients obtained are (in molecule-1 cm3 s-1): kCH3O2+CH3C(O)O2 = 1.2 × 10-11, kCH3O2+t-butylO2 = 3.0 × 10-15, kc-hexylO2+CH3O2 = 1.2 × 10-13, kt-butylO2+CH3C(O)O2 = 3.7 × 10-14, and kc-hexylO2+t-butylO2 = 1.5 × 10-15. In spite of their good comparison with the literature and good reproducibility, large uncertainties (×5/5) are recommended on these results because of those in the detection sensitivities. This work is a first illustration of the potential applications of this technique for the investigation of organic radicals in laboratory and in more complex systems.

Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence

We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO3-) and nitrite (NO2-) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO2 and N2, will produce nitric oxide (NO) when shocked by lightning. Photochemical reactions involving NO and H2O vapor will then produce acids such as HNO, HNO2, HNO3, and HO2NO2 that rain into the ocean. There, they dissociate into or react to form nitrate and nitrite. We present new calculations based on a novel combination of early-Earth global climate model and photochemical modeling, and we predict the flux of NOx to the Hadean ocean. In our 0.1-, 1-, and 10-bar pCO2 models, we calculate the NOx delivery to be 2.4 × 105, 6.5 × 108, and 1.9 × 108 molecules cm-2 s-1. After only tens of thousands to tens of millions of years, these NOx fluxes are expected to produce sufficient (micromolar) ocean concentrations of high-potential electron acceptors for the emergence of life. Key Words: Nitrogen oxides-Nitrate-Nitrite-Photochemistry-Lightning-Emergence of life. Astrobiology 17, 975-983.

The Reaction between Sodium Hydroxide and Atomic Hydrogen in Atmospheric and Flame Chemistry.

We report the first direct kinetic study of the gas-phase reaction NaOH + H → Na + H2O, which is central to the chemistry of sodium in the upper atmosphere and in flames. The reaction was studied in a fast flow tube, where NaOH was observed by multiphoton ionization and time-of-flight mass spectrometry, yielding k(NaOH + H, 230-298 K) = (3.8 ± 0.8) × 10-11 cm3 molecule -1 s-1 (at 2σ confidence level), showing no significant temperature dependence over the indicated temperature range and essentially in agreement with previous estimates of the rate constant in hydrogen-rich flames. We show, using theoretical trajectory calculations, that the unexpectedly slow, yet T-independent, rate coefficient for NaOH + H is explained by severe constraints in the angle of attack that H can make on NaOH to produce H2O. This reaction is also central to explaining Na-catalyzed flame inhibition, which has been proposed to occur via the sequence Na + OH (+ M) → NaOH followed by NaOH + H → Na + H2O, thereby effectively recombinating H and OH to H2O. RRKM calculations for the recombination of Na and OH yield k(Na + OH + N2, 300-2400 K) = 2.7 × 10-29 (300/T)1.2 cm6 molecule-2 s-1, in agreement with a previous flash photolysis measurement at 653 K and Na-seeded flame studies in the 1800-2200 K range. These results therefore provide strong evidence to support the mechanism of flame inhibition by Na.

Direct Probing of Criegee Intermediates from Gas-Phase Ozonolysis Using Chemical Ionization Mass Spectrometry.

Criegee intermediates (CIs), mainly formed from gas-phase ozonolysis of alkenes, are considered as atmospheric oxidants besides OH and NO3 radicals as well as ozone. Direct CI measurement techniques are inevitably needed for reliable assessment of CIs' role in atmospheric processes. We found that CIs from ozonolysis reactions can be directly probed by means of chemical ionization mass spectrometry with a detection limit of about 104-105 molecules cm-3. Results from quantum chemical calculations support the experimental findings. The simplest CI, CH2OO, is detectable as an adduct with protonated ethers, preferably with protonated tetrahydrofuran. Kinetic measurements yielded k(CH2OO + SO2) = (3.3 ± 0.9) × 10-11 and k(CH2OO + acetic acid) = (1.25 ± 0.30) × 10-10 cm3 molecule-1 s-1 at 295 ± 2 K, in very good agreement with recent measurements using diiodomethane photolysis for CH2OO generation. CIs from the ozonolysis of cyclohexene, acting as surrogate for cyclic terpenes, are followed as protonated species (CI)H+ using protonated amines as reagent ions. Kinetic investigations indicate a different reactivity of cyclohexene-derived CIs compared with that of simple CIs, such as CH2OO. It is supposed that the aldehyde group significantly influences the CI reactivity of the cyclohexene-derived CIs. The direct CI detection method presented here should allow study of the formation and reactivity of a wide range of different CIs formed from atmospheric ozonolysis reactions.

Wavelength-Resolved Photon Fluxes of Indoor Light Sources: Implications for HOx Production

Photochemistry is a largely unconsidered potential source of reactive species such as hydroxyl and peroxy radicals (OH and HO2, "HOx") indoors. We present measured wavelength-resolved photon fluxes and distance dependences of indoor light sources including halogen, incandescent, and compact fluorescent lights (CFL) commonly used in residential buildings; fluorescent tubes common in industrial and commercial settings; and sunlight entering buildings through windows. We use these measurements to predict indoor HOx production rates from the photolysis of nitrous acid (HONO), hydrogen peroxide (H2O2), ozone (O3), formaldehyde (HCHO), and acetaldehyde (CH3CHO). Our results suggest that while most lamps can photolyze these molecules, only sunlight and fluorescent tubes will be important to room-averaged indoor HOx levels due to the strong distance dependence of the fluxes from compact bulbs. Under ambient conditions, we predict that sunlight and fluorescent lights will photolyze HONO to form OH at rates of 106-107 molecules cm-3 s-1, and that fluorescent lights will photolyze HCHO to form HO2 at rates of ∼106 molecules cm-3 s-1; rates could be 2 orders of magnitude higher under high precursor concentrations. Ozone and H2O2 will not be important photochemical OH sources under most conditions, and CH3CHO will generally increase HO2 production rates only slightly. We also calculated photolysis rate constants for nitrogen dioxide (NO2) and nitrate radicals (NO3) in the presence of the different light sources. Photolysis is not likely an important fate for NO3 indoors, but NO2 photolysis could be an important source of indoor O3.

Significant OH production under surface cleaning and air cleaning conditions: Impact on indoor air quality.

We report measurements of hydroxyl (OH) and hydroperoxy (HO2 ) radicals made by laser-induced fluorescence spectroscopy in a computer classroom (i) in the absence of indoor activities (ii) during desk cleaning with a limonene-containing cleaner (iii) during operation of a commercially available "air cleaning" device. In the unmanipulated environment, the one-minute averaged OH concentration remained close to or below the limit of detection (6.5×105 moleculecm-3 ), whilst that of HO2 was 1.3×107 moleculecm-3 . These concentrations increased to ~4×106 and 4×108 moleculecm-3 , respectively during desk cleaning. During operation of the air cleaning device, OH and HO2 concentrations reached ~2×107 and ~6×108 moleculecm-3 respectively. The potential of these OH concentrations to initiate chemical processing is explored using a detailed chemical model for indoor air (the INDCM). The model can reproduce the measured OH and HO2 concentrations to within 50% and often within a few % and demonstrates that the resulting secondary chemistry varies with the cleaning activity. Whilst terpene reaction products dominate the product composition following surface cleaning, those from aromatics and other VOCs are much more important during the use of the air cleaning device.

Adsorption of bovine serum albumin on silicon dioxide nanoparticles: Impact of pH on nanoparticle-protein interactions.

Bovine serum albumin (BSA) adsorbed on amorphous silicon dioxide (SiO2) nanoparticles was studied as a function of pH across the range of 2 to 8. Aggregation, surface charge, surface coverage, and protein structure were investigated over this entire pH range. SiO2 nanoparticle aggregation is found to depend upon pH and differs in the presence of adsorbed BSA. For SiO2 nanoparticles truncated with hydroxyl groups, the largest aggregates were observed at pH 3, close to the isoelectric point of SiO2 nanoparticles, whereas for SiO2 nanoparticles with adsorbed BSA, the aggregate size was the greatest at pH 3.7, close to the isoelectric point of the BSA-SiO2 complex. Surface coverage of BSA was also the greatest at the isoelectric point of the BSA-SiO2 complex with a value of ca. 3 ± 1 × 1011 molecules cm-2. Furthermore, the secondary protein structure was modified when compared to the solution phase at all pH values, but the most significant differences were seen at pH 7.4 and below. It is concluded that protein-nanoparticle interactions vary with solution pH, which may have implications for nanoparticles in different biological fluids (e.g., blood, stomach, and lungs).

Heterogeneous Reactions of Limonene on Mineral Dust: Impacts of Adsorbed Water and Nitric Acid.

Biogenic volatile organic compounds (BVOCs), including the monoterpene limonene, are a major source of secondary organic aerosol (SOA). While gas-phase oxidation initiates the dominant pathway for BVOC conversion to SOA, recent studies have demonstrated that biogenic hydrocarbons can also directly react with acidic droplets. To investigate whether mineral dust may facilitate similar reactive uptake of biogenic hydrocarbons, we studied the heterogeneous reaction of limonene with mineral substrates using condensed-phase infrared spectroscopy and identified the formation of irreversibly adsorbed organic products. For kaolinite, Arizona Test Dust, and silica at 30% relative humidity, GC-MS identified limonene-1,2-diol as the dominant product with total organic surface concentrations on the order of (3-5) × 1018 molecules m-2. Experiments with 18O-labeled water support a mechanism initiated by oxidation of limonene by surface redox sites forming limonene oxide followed by water addition to the epoxide to form limonenediol. Limonene uptake on α-alumina, γ-alumina, and montmorillonite formed additional products in high yield, including carveol, carvone, limonene oxide, and α-terpineol. To model tropospheric processing of mineral aerosol, we also exposed each mineral substrate to gaseous nitric acid prior to limonene uptake and identified similar surface adsorbed products that were formed at rates 2 to 5 times faster than without nitrate coatings. The initial rate of reaction was linearly dependent on gaseous limonene concentration between 5 × 1012 and 5 × 1014 molecules cm-3 (0.22-20.5 ppm) consistent with an Eley-Rideal-type mechanism in which gaseous limonene reacts directly with reactive surface sites. Increasing relative humidity decreased the amount of surface adsorbed products indicating competitive adsorption of surface adsorbed water. Using a laminar flow tube reactor we measured the uptake coefficient for limonene on kaolinite at 25% RH to range from γ = 5.1 × 10-6 to 9.7 × 10-7. After adjusting for reactive surface areas, we estimate uptake coefficients for limonene on HNO3-processed mineral aerosol on the order of (1-6) × 10-6. Although this heterogeneous reaction will not impact the atmospheric lifetime of gaseous limonene, it does provide a new pathway for mineral aerosol to acquire secondary organic matter from biogenic hydrocarbons, which in turn will alter the physical properties of mineral dust.

Constraints on Arctic Atmospheric Chlorine Production through Measurements and Simulations of Cl2 and ClO

During springtime, unique halogen chemistry involving chlorine and bromine atoms controls the prevalence of volatile organic compounds, ozone, and mercury in the Arctic lower troposphere. In situ measurements of the chlorine monoxide radical, ClO, and its precursor, Cl2, along with BrO and Br2, were conducted using chemical ionization mass spectrometry (CIMS) during the Bromine, Ozone, and Mercury Experiment (BROMEX) near Barrow, Alaska, in March 2012. To our knowledge, these data represent the first ClO measurements made using CIMS. A maximum daytime ClO concentration of 28 ppt was observed following an early morning peak of 75 ppt of Cl2. A zero-dimensional photochemistry model was constrained to Cl2 observations and used to simulate ClO during a 7-day period of the field campaign. The model simulates ClO within the measurement uncertainty, and the model results highlight the importance of chlorine chemistry participation in bromine radical cycling, as well as the dependence of halogen chemistry on NOx levels. The ClO measurements and simulations are consistent with Cl2 being the dominant Cl atom source in the Arctic boundary layer. Simulated Cl atom concentrations, up to ∼1 × 106 molecules cm-3, highlight the importance of chlorine chemistry in the degradation of volatile organic compounds, including the greenhouse gas methane.

Coverage-dependent structural phase transformations in the adsorption of pentacene on an aperiodically modulated Cu film.

Surface ordering of pentacene molecules adsorbed on an aperiodic Cu surface has been studied with density functional theory (DFT) and scanning tunnelling microscopy as a function of coverage. Below 0.73 ML (5.3 × 1013 molecules cm-2), the adsorbate structure is row-like with the molecular axes aligned with the rows in the Cu structure. Between this coverage and 1 ML (7.3 × 1013 molecules cm-2), a structural phase with a checkerboard structure is seen. At this coverage region, the molecules are very close to each other which leads to unusual bending. At higher coverages, a further phase transition to a high-density row structure is seen for most of the film. DFT with van der Waals functionals is employed to study how the molecule-molecule and molecule-surface interactions evolve as a function of coverage.

THE PECULIAR DISTRIBUTION OF CH3CN IN IRC +10216 SEEN BY ALMA.

IRC +10216 is a circumstellar envelope around a carbon-rich evolved star which contains a large variety of molecules. According to interferometric observations, molecules are distributed either concentrated around the central star or as a hollow shell with a radius of ~15″. We present ALMA Cycle 0 band 6 observations of the J = 14 - 13 rotational transition of CH3CN in IRC +10216, obtained with an angular resolution of [Formula: see text]. The bulk of the emission is distributed as a hollow shell located at just ~2″ from the star, with a void of emission in the central region up to a radius of ~1″. This spatial distribution is markedly different from those found to date in this source for other molecules. Our analysis indicate that methyl cyanide is not formed neither in the stellar photosphere nor far in the outer envelope, but at radial distances as short as 1-2″, reaching a maximum abundance of ~ 0.02 molecules cm-3 at 2″ from the star. Standard chemical models of IRC +10216 predict that the bulk of CH3CN molecules should be present at a radius of ~ 15″, where other species such as polyyne radicals and cyanopolyynes are observed, with an additional inner component within 1″ from the star. The non-uniform structure of the circumstellar envelope and grain surface processes are discussed as possible causes of the peculiar distribution of methyl cyanide in IRC +10216.

The Reaction Kinetics of Amino Radicals with Sulfur Dioxide

Abstract Application of the laser photolysis–laser-induced fluorescence method to the reaction NH2 + SO2 in argon bath gas yields pressure-dependent, third-order kinetics which may be summarized as k = (1.49 ± 0.15) × 10−31 (T/298 K)−0.83 cm6 molecule –2 s –1 over 292–555 K, where the uncertainty is the 95% confidence interval and includes possible systematic errors. The quenching of vibrationally excited NH2 is consistent with a high-pressure limit for NH2 + SO2 of (1.62 ± 0.25) × 10−11 cm3 molecule –1 s –1 over the temperature range 295–505 K, where again the 95% confidence interval is shown. Ab initio analysis yields a H2N–SO2 dissociation enthalpy of 73.5 kJ mol –1, and comparison with RRKM theory and the exponential down model for energy transfer yields 〈ΔE〉down = 350 cm –1 for Ar at room temperature.

OClO and BrO observations in the volcanic plume of Mt. Etna – implications on the chemistry of chlorine and bromine species in volcanic plumes

Abstract. Spatial and temporal profiles of chlorine dioxide (OClO), bromine monoxide (BrO) and sulfur dioxide (SO2) of the volcanic plume at Mt. Etna, Italy, were investigated in September 2012 using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). OClO was detected in 119 individual measurements covering plume ages up to 6 min. BrO could be detected in 452 spectra up to 23 min downwind. The retrieved slant column densities (SCDs) reached maximum values of 2.0 × 1014 molecules cm-2 (OClO) and 1.1 × 1015 molecules cm-2 (BrO). Mean mixing ratios of BrO and OClO were estimated assuming a circular plume cross section. Furthermore, ClO mixing ratios were derived directly from the BrO and OClO-SCDs. Average abundances of BrO = 1.35 ppb, OClO = 300 ppt and ClO = 139 ppt were found in the young plume (plume age τ < 4 min) with peak values of 2.7 ppb (BrO), 600 ppt (OClO) and 235 ppt (ClO) respectively. The chemical evolution of BrO and OClO in the plume was investigated in great detail by analysing the OClO/SO2 and BrO/SO2 ratios as a function of plume age τ. A marked increase of both ratios was observed in the young plume (τ < 142 s) and a levelling off at larger plume ages showing mean SO2 ratios of 3.17 × 10-5 (OClO/SO2) and 1.65 × 10-4 (BrO/SO2). OClO was less abundant in the plume compared to BrO with a mean OClO/BrO ratio of 0.16 at plume ages exceeding 3 min. A measurement performed in the early morning at low solar radiances revealed BrO/SO2 and OClO/SO2 ratios increasing with time. This observation substantiates the importance of photochemistry regarding the formation of BrO and OClO in volcanic plumes. These findings support the current understanding of the underlying chemistry, namely, that BrO is formed in an autocatalytic, heterogeneous reaction mechanism (in literature often referred to as "bromine explosion") and that OClO is formed in the reaction of OClO with BrO. These new findings, especially the very detailed observation of the BrO and OClO formation in the young plume, were used to infer the prevailing Cl-atom concentrations in the plume. Relatively small values ranging from [Cl] = 2.5 × 106 cm-3 (assuming 80 ppb background O3) to [Cl] = 2.0 × 108 cm-3 (at 1 ppb O3) were calculated at plume ages of about 2 min. Based on these Cl abundances, a potential – chlorine-induced – depletion of tropospheric methane (CH4) in the plume was investigated. CH4 lifetimes between 14 h (at 1 ppb O3) and 47 days (at 80 ppb O3) were derived. While these lifetimes are considerably shorter than the atmospheric lifetime of CH4, the impact of gaseous chlorine on the CH4 budget in the plume environment should nevertheless be relatively small due to plume dispersion (decreasing Cl concentrations) and ongoing mixing of the plume with the surrounding atmosphere (replenishing O3 and CH4). In addition, all spectra were analysed for signatures of IO, OIO and BrO. None of these species could be detected. Upper limits for IO/SO2, OIO/SO2 and OBrO/SO2 are 1.8 × 10-6, 2.0 × 10-5 and 1.1 × 10-5 respectively.

Rate constant and thermochemistry for K + O2 + N2 = KO2 + N2.

The addition reaction of potassium atoms with oxygen has been studied using the collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) method. KCl vapor was photolyzed with 266 nm pulses and the absorbance by K atoms at 766.5 nm was measured at various delay times with a narrow line width diode laser. Experiments were carried out with O2/N2 mixtures at a total pressure of 1 bar, over 748-1323 K. At the lower temperatures single exponential decays of [K] yielded the third-order rate constant for addition, kR1, whereas at higher temperatures equilibration was observed in the form of double exponential decays of [K], which yielded both kR1 and the equilibrium constant for KO2 formation. kR1 can be summarized as 1.07 × 10(-30)(T/1000 K)(-0.733) cm(6) molecule(-2) s(-1). Combination with literature values leads to a recommended kR1 of 5.5 × 10(-26)T(-1.55) exp(-10/T) cm(6) molecule(-2) s(-1) over 250-1320 K, with an error limit of a factor of 1.5. A van't Hoff analysis constrained to fit the computed ΔS298 yields a K-O2 bond dissociation enthalpy of 184.2 ± 4.0 kJ mol(-1) at 298 K and ΔfH298(KO2) = -95.2 ± 4.1 kJ mol(-1). The corresponding D0 is 181.5 ± 4.0 kJ mol(-1). This value compares well with a CCSD(T) extrapolation to the complete basis set limit, with all electrons correlated, of 177.9 kJ mol(-1).

SO<sub>2</sub> photolysis as a source for sulfur mass-independent isotope signatures in stratospehric aerosols

Abstract. Signatures of sulfur isotope mass-independent fractionation (S-MIF) have been observed in stratospheric sulfate aerosols deposited in polar ice. The S-MIF signatures are thought to be associated with stratospheric photochemistry following stratospheric volcanic eruptions, but the exact mechanism responsible for the production and preservation of these signatures is debated. In order to identify the origin and the mechanism of preservation for these signatures, a series of laboratory photochemical experiments were carried out to investigate the effect of temperature and added O2 on the S-MIF produced by two absorption band systems of SO2: photolysis in the 190 to 220 nm region and photoexcitation in the 250 to 350 nm region. The SO2 photolysis (SO2 + hν → SO + O) experiments showed S-MIF signals with large 34S/34S fractionations, which increases with decreasing temperature. The overall S-MIF pattern observed for photolysis experiments, including high 34S/34S fractionations, positive mass-independent anomalies in 33S, and negative anomalies in 36S, is consistent with a major contribution from optical isotopologue screening effects and data for stratospheric sulfate aerosols. In contrast, SO2 photoexcitation produced products with positive S-MIF anomalies in both 33S and 36S, which is different from stratospheric sulfate aerosols. SO2 photolysis in the presence of O2 produced SO3 with S-MIF signals, suggesting the transfer of the S-MIF anomalies from SO to SO3 by the SO + O2 + M → SO3 + M reaction. This is supported with energy calculations of stationary points on the SO3 potential energy surfaces, which indicate that this reaction occurs slowly on a single adiabatic surface, but that it can occur more rapidly through intersystem crossing. Based on our experimental results, we estimate a termolecular rate constant on the order of 10−37 cm6 molecule−2 s−1. This rate can explain the preservation of mass independent isotope signatures in stratospheric sulfate aerosols and provides a minor, but important, oxidation pathway for stratospheric SO2. The production and preservation of S-MIF signals requires a high SO2 column density to allow for optical isotopologue screening effects to occur and to generate a large enough signature that it can be preserved. In addition, the SO2 plume must reach an altitude of around 20 to 25 km, where SO2 photolysis becomes a dominant process. These experiments are the first step towards understanding the origin of the sulfur isotope anomalies in stratospheric sulfate aerosols.

Pressure Dependence and Kinetic Isotope Effects in the Absolute Rate Constant for Methoxy Radical Reacting with NO2

ABSTRACTWe have investigated the kinetics for the reaction CH3O• + NO2 in N2 bath gas. The rate constants are well‐fit by the Troe expression over the temperature (250–335 K) and pressure range (30–700 Torr) investigated. The termolecular rate constant is given by cm6 molecule−2 s−1, and the rate constant at the high‐pressure limit is given by cm3 molecule−1 s−1. We also studied the kinetics of the reaction of CD3O• + NO2 as a function of temperature and pressure under similar conditions as those for CH3O• + NO2. The resulting low‐ and high‐pressure limiting rate constants are cm6 molecule−2 s−1 and cm3 molecule−1 s−1, respectively. The rate constants for the two isotopologues track each other closely as the high‐pressure limit is approached. The present results agree with most previous results at 295 K over a range of pressures, but there is substantial disagreement about the temperature dependence.

New determination of the HCN profile in the stratosphere of Neptune from millimeter-wave spectroscopy

Context. Periodic monitoring of the atmospheric composition is the cornerstone of planetary atmospheric science. It reveals temporal and/or spatial variations. Ground-based observations of rotational lines from the (sub-)millimeter wavelength range is a suitable method to obtain the mean HCN profile in Neptune's startosphere. Aims: We aimed at deriving new constraints on the disk-averaged HCN stratospheric profile and abundance. The 14-year gap between the last published observations and ours of HCN in Neptune can be used to constrain any possible time variation of this main nitrogen-bearing molecule at the probed altitudes. This temporal variation could additionally reveal, albeit indirectly, the dominant process responsible for the origin of the nitrogen compoundsin the stratosphere of Neptune. Methods: Spectra of the HCN (J = 3-2) line at 265.886 GHz were obtained with the 1.3 mm receiver of the Submillimeter Telescope (SMT) at the Arizona Radio Observatory (ARO) using several backends simultaneously. The spectral resolution of the analyzed datasets was 1 MHz and 250 kHz, providing a signal-to-noise ratio of 20 and 11, respectively. Pre-processing of the spectra involved baseline removal and de-noising using the empirical mode decomposition technique. The spectra were then inverted using a line-by-line radiative transfer model to obtain the vertical profile of HCN between 2 mbar to 10 μbar and derive the column density. Results: The retrieved mean stratospheric HCN mole fraction is (1.3 ± 0.6) × 10-9 above 0.5 millibar, corresponding to a column density of 2.2 × 1014 molecules cm-2. The data are consistent with a pronounced HCN decrease below the 0.6 mbar level, which agrees with previous findings.

Fate in the environment and long-range atmospheric transport of the organophosphorus insecticide, chlorpyrifos and its oxon.

The fate and movement of the organophosphorus insecticide chlorpyrifos (CPY;CAS No.2921-88-2) and its metabolite chlorpyrifos-oxon (CPYO; CASNo.5598-15-2) determine exposures in terrestrial and aquatic environments.Detectable concentrations of the organophosphorus insecticide CPY in air, rain,snow and other environmental media have been measured in North America and other locations at considerable distances from likely agricultural sources, which indicates the potential for long range transport (LRT) in the atmosphere. This issue was addressed by first compiling monitoring results for CPY in all relevant environmental media. As a contribution to the risk assessment of CPY in remote regions, a simple mass balance model was developed to quantify likely concentrations at locations ranging from local sites of application to more remote locationsup to hundreds of km distant. Physical-chemical properties of CPY were reviewed and a set of consistent values for those properties that determine partitioning and reactivity were compiled and evaluated for use in the model. The model quantifies transformation and deposition processes and includes a tentative treatment of dispersion to lesser atmospheric concentrations. The model also addressed formation and fate of CPYO, which is the major transformation product of CPY. The Characteristic Travel Distance (CTD) at which 63% of the original mass of volatilized CPY is degraded or deposited-based on a conservative concentration of •OHradicals of 0.7 x 106 molecules cm-3 and a half-life of 3 h, was estimated to be 62 km. At lesser concentrations of •OH radical, such as occurs at night and at lesser temperatures, the CTD is proportionally greater. By including monitoring data from a variety of media, including air, rain, snow and biota, all monitored concentrations can be converted to the equilibrium criterion of fugacity, thus providing asynoptic assessment of concentrations of CPY and CPYO in multiple media. The calculated fugacities of CPY in air and other media decrease proportionally with increasing distance from sources, which can provide an approximate prediction of downwind concentrations and fugacities in media and can contribute to improved risk assessments for CPY and especially CPYO at locations remote from points of application, but still subject to LRT. The model yielded estimated concentrations that are generally consistent with concentrations measured, which suggests that the canonical fate and transport processes were included in the simulation model. The equations included in the model enable both masses and concentrations of CPY and CPYO to be estimated as a function of distance downwind following application.While the analysis provided here is useful and an improvement over previous estimates of LRT of CPY and CPYO, there is still need for improved estimates of the chemical-physical properties of CPYO.Based on the persistence in water, soils, and sediments, its bioconcentration and biomagnification in organisms, and its potential for long-range transport, CPY and CPYO do not trigger the criteria for classification as a POP under the Stockholm convention or a PB chemical under EC 1107/2009. Nonetheless, CPY is toxic at concentrations less than the trigger for classification as T under EC 11 07 /2009; however,this simple trigger needs to be placed in the context of low risks to non-target organisms close to the areas of use. Overall, CPY and CPYO are judged to not trigger the PBT criteria of EC 1107/2009.

Kinetic Study of the CCl2Radical Recombination Reaction by Laser-Induced Fluorescence Technique

Fil: Gomez, Nicolas Damian. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Investigaciones Cientificas y Tecnicas para la Defensa. Centro de Investigacion en Laseres y Aplicaciones; Argentina

What, Methane Again?!

A combination of an error discovered in the Multiwell code and some more recent examinations of the system CH3 + H = CH4 prompted a reexamination of earlier work by this author. Values of the energy transfer parameter, 〈ΔEd〉, are considerably different from the previous study. It is suggested that the Baulch et al. parameters for this system can be improved by replacing the values for krec,0 and krec,∞ with values suggested by Troe and Ushakov. krec,0 = [Ar] 10−26.19 exp[–(T/21.22 K)0.5] cm6 molecule−2 s−1, krec,∞ = 3.34 × 10−10 (T/25200 K)0.186 cm3 molecule−1 s−1 while keeping their value for Fc = 0.63 exp(–T/3315) + 0.37 exp(–T/61).