Concentration Of Chlorine Atoms Research Articles

Formulation of the cosmic ray–driven electron-induced reaction mechanism for quantitative understanding of global ozone depletion

This paper formulates the cosmic ray-driven electron-induced reaction as a universal mechanism to provide a quantitative understanding of global ozone depletion. Based on a proposed electrostatic bonding mechanism for charge-induced adsorption of molecules on surfaces and on the measured dissociative electron transfer (DET) cross sections of ozone-depleting substances (ODSs) adsorbed on ice, an analytical equation is derived to give atmospheric chlorine atom concentration: [Formula: see text] where Φe is the prehydrated electron (epre-) flux produced by cosmic ray ionization on atmospheric particle surfaces, [Formula: see text] is the surface coverage of an ODS, and ki is the ODS's effective DET coefficient that is the product of the DET cross section, the lifetimes of surface-trapped epre- and Cl-, and the particle surface area density. With concentrations of ODSs as the sole variable, our calculated results of time-series ozone depletion rates in global regions in the 1960s, 1980s, and 2000s show generally good agreement with observations, particularly with ground-based ozonesonde data and satellite-measured data over Antarctica and with satellite data in a narrow altitude band at 13 to 20 km of the tropics. Good agreements with satellite data in the Arctic and midlatitudes are also found. A previously unreported effect of denitrification on ozone loss is found and expressed quantitatively. But this equation overestimates tropospheric ozone loss at northern midlatitudes and the Arctic, likely due to increased ozone production by the halogen chemistry in polluted regions. The results render confidence in applying the equation to achieve a quantitative understanding of global ozone depletion.

On the Effect of the Cl2 + O2 + Ar Mixture Composition on the Concentrations of Chlorine and Oxygen Atoms in a Plasma

On the Effect of the Cl2 + O2 + Ar Mixture Composition on the Concentrations of Chlorine and Oxygen Atoms in a Plasma

Effect of Titanium tetrachloride on the rate of chlorination of Yarega quartz-leucoxene concentrate

This paper considers the results of a study that looked at chlorination of the Yarega quartz-leucoxene concentrate in an ebullated bed reactor (EBR) that feeds titanium tetrachloride vapours and their mixture with chlorine to the reaction mass. The experiments were conducted at a temperature of 850 oC and an incoming gas flow rate of 1,600 ml/min. 250–315 μm concentrate grains mixed with 160–250 μm calcined petroleum coke (the carbon to titanium dioxide molecular ratio was 5) were subjected to chlorination. The reaction products were analyzed with the help of inductively coupled plasma optical emission spectroscopy. It was found that, in the absence of chlorine, titanium tetrachloride only interacts with iron oxides. Feeding a mixture of titanium tetrachloride vapours and chlorine into the reactor leads to an intensified chlorination of the main concentrate components, including TiO2, SiO2, Al2O3 and Fe2O3. The TiO2 chlorination rate rises proportionally to the square root of the partial pressure of titanium tetrachloride in the gas-vapour mixture. The risen rate can be attributed to a higher concentration of active chlorine atoms, which in this case occur on carbon surface not only due to dissociation of molecular chlorine but also as a result of decomposition of titanium tetrachloride. A higher partial pressure of chlorine atoms leads to higher rates of reaction between the chlorine atoms and the concentrate components. According to the proposed reaction mechanism, the TiO2 chlorination rate is proportional to the square root of the product of the partial pressure of TiCl4 and the carbon grains surface area. The excessive chlorine does not impact the chlorination rate. It would be advisable to take into account the discovered ability of TiCl4 to intensify the titanium dioxide chlorination process when designing a chlorine feeding unit in the ebullated bed reactor. Feeding chlorine mixed with titanium tetrachloride vapours into the lower section of the reactor can help enhance the process performance while avoiding using too much chlorine.The work weas carried out under financial support of the Russian Foundation for Basic Research grant, the project No. 18-29-24187mk.

Effect of a Mixture’s Composition on the Electrophysical Parameters and Emission Spectra of Hydrogen Chloride Plasma with Chlorine and Helium

The effect of a mixture’s composition on the electrophysical parameters and emission spectra of HCl/Cl2 and HCl/He plasmas under the conditions of a DC glow discharge is analyzed. The data on the gas temperature and reduced electric field strength are obtained. It is established that the reduced electric field strength in HCl/Cl2 plasma rises linearly with the rising fraction of the second gas in the mixture, while the same value in the HCl/He plasma decreases. It is shown that, in the HCl/Cl2 plasma with a variable composition, the atomic chlorine concentration remains practically unchanged, whereas, in the HCl/He plasma, it decreases monotonically.

A Large Source of Atomic Chlorine From ClNO2 Photolysis at a U.K. Landfill Site

AbstractNitryl chloride (ClNO2) acts as a source of highly reactive chlorine atoms as well as an important NOx reservoir. Measurements of ClNO2 at an operational U.K. landfill site are reported here for the first time. A peak concentration of 4 ppb of ClNO2 was found with a peak mean nighttime maximum of 0.9 ppb. Using models based upon the photolysis of observed ClNO2 and atmospheric chlorine chemistry, chlorine atom concentrations reaching in excess of 1.20 × 105 molecules/cm3 in the early morning following sunrise are calculated. These concentrations are approximately 10 times higher than previously reported in the United Kingdom, suggesting a significant impact on the oxidizing capacity around such sites. Given the ubiquity of landfill sites regionally and globally, and the large abundances of Cl atoms from the photolysis of ClNO2, chlorine chemistry has a significant impact on ozone formation and volatile organic compounds oxidation as shown by WRF‐Chem modeling.

Ignition induced the short-term action of UV light as possible evidence of chain branching in the reacting CH3Cl + Cl2 mixture

Ignition takes place in a mixture of chloromethane and chlorine at atmospheric pressure and room temperature 0.1 s after the irradiation of the mixture with a UV light pulse from a mercury quartz lamp. Temperature fields are presented, which demonstrate the development of the ignition process in the dark period. Calculations show that, after the initiation is stopped, the concentration of chlorine atoms decreases to a critical value within a time of the order of 0.02 s. The observed ignition can be explained by chains branching caused by the decay of the excited CCl 3 * radical that have accumulated energy upon the successive substitution of chlorine atoms for hydrogen in the chloromethane molecule.

Measuring the rate constant of the reaction between chlorine atoms and CHF2Br by Cl atom resonance fluorescence

The rate constant of the reaction between Cl atoms and CHF2Br has been measured by chlorine atom resonance fluorescence in a flow reactor at temperatures of 295–368 K and a pressure of ~1.5 Torr. Lining the inner surface of the reactor with F-32L fluoroplastic makes the rate of the heterogeneous loss of chlorine atoms very low (k het ≤ 5 s–1). The rate constant of the reaction is given by the formula k = (4.23 ± 0.13) × 10–12 e (–15.56 ± 1.58)/RT cm3 molecule–1 s–1 (with the activation energy in kJ/mol units). The possible role of this reaction in the extinguishing of fires producing high concentrations of chlorine atoms is discussed.

Electrophysical parameters and concentrations of active particles in the plasma of HCl mixtures with inert and molecular gases

Electrophysical parameters in HCl-Ar, HCl-H2, and HCl-Cl2 mixtures are studied under conditions of the direct-current (DC) glow discharge. It is shown that there is no increasing in the concentration of atomic chlorine in HCl-Ar and, in HCl-H2 and there are no significant changes in the kinetics of atomicmolecular processes and, therefore, in the balance of neutral particles in the plasma. The increase in the concentration of admixture gas in HCl-Cl2 is accompanied by the monotonic increase in the concentration of chlorine atoms and the density of their flux to the surface that bounds the plasma volume.

Kinetics and concentration of chlorine atoms in hydrogen chloride-argon plasma

The mechanisms of the influence of the initial composition of an HCl-Ar mixture on the kinetics and concentration of chlorine atoms in direct-current glow discharge plasma have been studied. It has been found that an increase in the Ar content at a constant total gas pressure leads to an increase in the degree of dissociation of HCl due to an increase in the electron impact dissociation efficiency.

The effect of chlorine atoms on the charging kinetics of carbon nanoparticles forming in shock-heated plasma

This work continues the study on the charging kinetics of soot during the formation of carbon nanoparticles in hydrogen-free systems upon the pyrolysis of carbon-containing materials behind shock waves. The experimental results and results of computer simulation of electrical charging of the carbon nanoparticles formed during the pyrolysis of CCl4 behind the shock waves are given. It is shown that the natural impurity of sodium atoms amounting to 1012–1013 cm−3 are the main source of free electrons. It is established that the time required for relaxation of the charge distribution in the gas-nanoparticle system at 15–30 bar decreases from 400 to 100 μs in a 0.5% CCl4 + Ar mixture with increasing the equilibrium temperature from 2000 to 3600 K and from 350 to 50 μs in a 5% CCl4 + Ar mixture with increasing the equilibrium temperature from 1500 to 2500 K. The equilibrium concentration of free electrons in the presence of the nanoparticles in the system decreases by one to two orders of magnitude compared to that in the system without nanoparticles. The presence of chlorine atoms in the mixture leads to a considerable decrease in the concentration of electrons in the gas-nanoparticle system and to a decrease in the concentration of charged nanoparticles. The electron kinetics in the mixtures under consideration is characterized by a high (as compared with sodium) concentration of chlorine atoms having a larger electron affinity.

Vertical transport rates and concentrations of OH and Cl radicals in the Tropical Tropopause Layer from observations of CO<sub>2</sub> and halocarbons: implications for distributions of long- and short-lived chemical species

Abstract. 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.

A low energy pathway to CuCl2 at Cu(110) surfaces

The reaction of hydrogen chloride gas with partially oxidised Cu(110) surfaces follows a different structural pathway than its reaction with a clean surface. In the latter case a c(2 x 2)Cl structure develops which is compressed in the [110] direction for chlorine atom concentrations greater than 5.5 x 10(14) cm(-2). In contrast, the presence of oxygen leads to the formation of linear "Cl-chains" orientated in the [100] direction which closely resemble those of bulk CuCl(2). These Cu(II) like structures are unstable at room temperature decomposing to form c(2 x 2)Cl. Using XPS and STM we have investigated the formation of the CuCl(2) like surface species and propose that it derives from the unusual reactivity of transient copper adatoms released from the p(2 x 1)O by the exothermic formation of water.

The Kinetic Mechanisms of the Trapping of Atmospheric Gases by Marine Salt Surfaces: IX. The Heat of Adsorption of Cl Atoms on the Surface of NaCl

The heterogeneous trapping of chlorine atoms on the surface of NaCl was studied using two coaxial stream reactors connected to an EPR cavity or a mass spectrometer. The kinetics of trapping was measured by the EPR method over a wide range of chlorine atom concentrations (1010–1013 cm−3) at temperatures of 250–330 K. At [Cl] ≥ 1012 cm−3, chlorine atoms were recorded by the EPR method in the gas phase. At lower concentrations (~1010−3 × 1011 cm−3), Cl atoms were replaced with RO2 radicals by adding hexane RH and O2 at the entrance of the EPR cavity. This was followed by the matrix isolation of RO2 in the cavity at liquid nitrogen temperature. The probability of the trapping of chlorine atoms on the chemically inactive surface of NaCl was found to increase as the concentration of Cl grew. The temperature dependence of the trapping coefficient γ was pronounced at a concentration of chlorine atoms of ~3 × 1010 cm−3, whereas no such dependence was observed at a chlorine concentration of ~ 1013 cm−3. The recombination of Cl atoms was well described by the Rideal-Eley mechanism, and the heat of adsorption of chlorine atoms on the inactive surface of NaCl was estimated at Q = 17 ± 0.6 kcal/mol. It was shown mass spectrometrically that the trapping coefficient γ of Cl atoms decreased with the time of measurements, like the partial coefficient of the formation of the HCl product, whereas the partial coefficient of the formation of the Cl2 product, conversely, increased with the time. The characteristic time of the attainment of stationary values by all the γ coefficients weakly depended on the initial concentration of Cl and equaled several dozen seconds. Reactions of adsorbed Cl atoms formed in the trapping of NO3 radicals by the surface of marine salt NaCl in coastal troposphere are discussed.

Surface characterization of photodegraded dyed styrene butadiene and natural rubbers

AbstractThe combination of laser ablation coupled to mass spectrometry, Ultraviolet‐visible spectroscopy and environmental scanning electron microscopy (coupled with energy dispersive X‐ray spectrometry EDX) as independent techniques to investigate the surface photooxidation of dyed filled natural rubber (NR) and styrene butadiene rubber (SBR), designed for outdoor applications, have been investigated. The aging results in the deterioration of the exposed surface material properties. Results indicate that dyed filled NR and SBR samples behave differently during the photooxidation. The fading of the dyed polymers was found to be promoted in the NR sample. This is proved by the disappearance of [M − H]− pseudomolecular ion of orange pigment and also its fragment ions after aging, which was detected by LDI–FTICRMS. This is confirmed by both EDX and UV/vis spectroscopy. EDX analysis indicates a concentration of chlorine atoms, which is a marker of orange pigment or of its degradation products, at the surface of SBR flooring after aging, which is not observed with NR. Reactivity of the radicals formed during flooring aging is thought to greatly affect the behavior of the organic pigment and is discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Study of Polymer Material Aging by Laser Mass Spectrometry, UV-Visible Spectroscopy, and Environmental Scanning Electron Microscopy

Dyed natural rubber (NR) and styrene butadiene rubber (SBR), designed for outdoor applications, were exposed to an accelerated artificial aging in xenon light. The aging results in the deterioration of the exposed surface material properties. The ability of dyed polymers to withstand prolonged sunlight exposure without fading or undergoing any physical deterioration is largely determined not only by the photochemical characteristics of the absorbing dyestuff itself but also by the polymer structure and fillers. Results obtained by laser mass spectrometry, UV-visible spectroscopy, and environmental scanning electron microscopy indicate that dyed filled NR and SBR samples behave differently during the photo-oxidation. The fading of the dyed polymers was found to be promoted in the NR sample. This can be correlated with LDI-FTICRMS results, which show the absence of [M-H]− orange pigment pseudomolecular ion and also its fragment ions after aging. This is confirmed by both EDX and UV/Vis spectroscopy. EDX analysis indicates a concentration of chlorine atoms, which can be considered as a marker of orange pigment or its degradation products, only at the surface of SBR flooring after aging. Reactivity of radicals formed during flooring aging has been studied and seems to greatly affect the behavior of such organic pigments.

Primary product distribution from the Cl-atom initiated atmospheric degradation of furan: Environmental implications

Furan is an aromatic hydrocarbon present in both urban and rural atmospheres, which is emitted mainly by biomass burning and the combustion of fossil fuel. Reaction of furan and Cl atoms may be important in areas where chlorine atom concentrations are potentially high such as marine and coastal regions or continental atmospheres where industrial activity emits molecular chlorine or photo-labile Cl-containing compounds. To assess the importance of this reaction and to investigate whether any unique chlorine-containing product is formed the products of the reaction of Cl atoms with furan have been determined under atmospheric conditions. For the study two different sampling/detection methods have been used: (1) Solid-Phase MicroExtraction, with subsequent analysis by thermal desorption, and gas chromatography with mass spectrometry or flame ionization detection (SPME/GC-MS/FID), and 2-“in situ” with long path fourier transform infrared spectroscopy (FTIR). The yields of primary reaction products in the absence of NO were: 5-chloro-2(5H)-furanone (64.5±10.7)%, E-butenedial (11±3)%, 5-hydroxy-2(5H)-furanone (⩽2.4%) and Z-butenedial (1.6±0.5)%. Other products generated by secondary reactions were 2(3H)-furanone (2.8±1.9)%, HCl (21.1±3%) and CO. Maleic anhydride was detected with a yield of about 2%, however, this yield may be a combination of both primary and secondary reactions. All errors are ±2 σ. The observed products confirm that addition of Cl atoms to the double bond of furan is the dominant reaction pathway.

Atomic chlorine concentrations derived from ethane and hydroxyl measurements over the equatorial Pacific Ocean: Implication for dimethyl sulfide and bromine monoxide

Atomic chlorine and bromine monoxide concentrations ([Cl] and [BrO]) and dimethyl sulfide (DMS) sea‐air fluxes are estimated from data collected during a Lagrangian flight made near Christmas Island (2°N, 157°W) during August 1996 aboard the NASA P3‐B aircraft. Intensive hydrocarbon sampling began in the surface layer (SL) one‐half hour after sunrise and continued until ∼1300 local solar time. Our empirical model includes in situ observations of hydroxyl [HO] and precise measurements of ethane (C2H6) mixing ratios. Ethane was ∼40 pptv higher in the buffer layer (BuL) than in the SL, thus vertical exchange tended to replace any C2H6 that was photochemically removed in the SL. In spite of this, SL C2H6 mixing ratios decreased significantly during the flight. Using only the measured [HO] and estimated vertical mixing, our mass balance equation cannot explain all of the observed SL C2H6 loss. However, when an initial [Cl] of 8.4 (±2.0) × 104 Cl cm−3, decreasing to 5.7 (±2.0) × 104 Cl cm−3 at midday, is included, the observed and estimated C2H6 values are in excellent agreement. Using our [Cl], we estimate a DMS flux a factor of 2 higher than when HO is the only oxidant considered. This flux estimate, when compared to that derived by Lenschow et al. (1999), suggests that if the differences are real, we may be missing a loss term. Best agreement occurs when an average BrO mixing ratio of 1.3 (±1.3) pptv is included in our mass balance equation.

Formation of Bromochlorodibenzo-p-dioxins and Furans from the High-Temperature Pyrolysis of a 2-Chlorophenol/2-Bromophenol Mixture

The homogeneous, gas-phase pyrolytic thermal degradation of a 50:50 mixture of 2-bromophenol and 2-chlorophenol was studied in a 1 cm i.d., fused silica flow reactor at a total concentration of 88 ppm, reaction time of 2.0 s, and temperatures from 300 to 1000 degrees C. Observed products included (in decreasing yield) naphthalene, dibenzo-p-dioxin (DD), phenol, dibenzofuran (DF), bromobenzene, chloronaphthalene, 4-bromo-6-chlorodibenzofuran (4-B,6-CDF), bromonaphthalene, benzene, 4,6-dichlorodibenzofuran (4,6-DCDF), chlorobenzene, 4-monobromodibenzofuran (4-MBDF), 4-monochlorodibenzofuran (4-MCDF), 1-mono-bromodibenzo-p-dioxin (1-MBDD), 2-chloro,4-bromophenol, 2,4-dibromophenol, and 2-bromo-4-chlorophenol. Unlike the case for the pyrolysis of pure 2-chlorophenol, 4,6-DCDF was observed, but the analogous 4,6-DBDF remained undetected similar to the individual results with 2-MBP. This indicates that the presence of bromine increases the concentration of chlorine atoms available for the formation of 4,6-DCDF. Due to bromine atoms acting as better leaving groups than chlorine atoms, the yield of DD was increased over that observed for the pyrolysis of 2-chlorophenol. The addition of bromine to a chlorinated hydrocarbon system results in an increase in the total yield of PCDD/Fs as well as PBDD/Fs and mixed PBCDD/Fs due to the ease of bromine elimination reactions as well as an increase of the chlorine atom concentration.

Temperature and Pressure Dependent Rate Coefficients for the Reaction of Hg with Cl and the Reaction of Cl with Cl: A Pulsed Laser Photolysis−Pulsed Laser Induced Fluorescence Study

A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the recombination of mercury and chlorine atoms, Hg + Cl + M --> HgCl + M (1), and the self-reaction of chlorine atoms, Cl + Cl + M --> Cl(2) + M (2). Rate coefficients were determined as a function of pressure (200-600 Torr) and temperature (243-293 K) in N(2) buffer gas and as a function of pressure (200-600 Torr) in He buffer gas at room temperature. For reaction (1) kinetic measurements were obtained under conditions in which either mercury or chlorine atoms were the reactant in excess concentration while simultaneously monitoring the concentration of both reactants. An Arrhenius expression of (2.2 +/- 0.5) x 10(-32) exp{(680 +/- 400)((1)/(T) - (1)/(298))} cm(6) molecule(-2) s(-1) was determined for the third-order recombination rate coefficient in nitrogen buffer gas. The effective second-order rate coefficient for reaction 1 under atmospheric conditions is much smaller than prior determinations using relative rate techniques. For reaction (2) we obtain an Arrhenius expression of (8.4 +/- 2.3) x 10(-33) exp{(850 +/- 470)((1)/(T) - (1)/(298))} cm(6) molecule(-2) s(-1) for the third-order recombination rate coefficient in nitrogen buffer gas. The rate coefficients are reported with a 2sigma error of precision only; however, due to the uncertainty in the determination of absolute chlorine atom concentrations we conservatively estimate an uncertainty of +/-50% in the rate coefficients. For both reactions the observed pressure, temperature, and buffer gas dependencies are consistent with the expected behavior for three-body recombination.

Barium–strontium–titanate etching characteristics in chlorinated discharges

The etching characteristics of barium–strontium–titanate (BST) were investigated using a high-density plasma sustained by surface waves at 190 MHz in Ar/Cl2 gas mixtures. The etch rate was examined as a function of both the total gas pressure and the Cl2 fraction in Ar/Cl2 using a wafer temperature of 10 °C. The results were correlated to positive ion density and plasma composition obtained from Langmuir probes and mass spectrometry. The BST etch rate was found to increase linearly with the positive ion density and to decrease with increasing chlorine atom concentration. This result indicates that for the temperature conditions used, the interaction between chlorine and BST yields compounds having a volatility that is lower than the original material. As a consequence, the contribution of neutral atomic Cl atoms to the etch mechanism is detrimental, thereby reducing the etch rate. As the wafer temperature increases, the role of chemistry in the etching process is enhanced.