Cl2 Concentration Research Articles

Observations of organic and inorganic chlorinated compounds and their contribution to chlorine radical concentrations in an urban environment in northern Europe during the wintertime

Abstract. A number of inorganic (nitryl chloride, ClNO2; chlorine, Cl2; and hypochlorous acid, HOCl) and chlorinated, oxygenated volatile organic compounds (ClOVOCs) have been measured in Manchester, UK during October and November 2014 using time-of-flight chemical ionisation mass spectrometry (ToF-CIMS) with the I− reagent ion. ClOVOCs appear to be mostly photochemical in origin, although direct emission from vehicles is also suggested. Peak concentrations of ClNO2, Cl2 and HOCl reach 506, 16 and 9 ppt respectively. The concentrations of ClNO2 are comparable to measurements made in London, but measurements of ClOVOCs, Cl2 and HOCl by this method are the first reported in the UK. Maximum HOCl and Cl2 concentrations are found during the day and ClNO2 concentrations remain elevated into the afternoon if photolysis rates are low. Cl2 exhibits a strong dependency on shortwave radiation, further adding to the growing body of evidence that it is a product of secondary chemistry. However, night-time emission is also observed. The contribution of ClNO2, Cl2 and ClOVOCs to the chlorine radical budget suggests that Cl2 can be a greater source of Cl than ClNO2, contributing 74 % of the Cl radicals produced on a high radiant-flux day. In contrast, on a low radiant-flux day, this drops to 14 %, as both Cl2 production and loss pathways are inhibited by reduced photolysis rates. This results in ClNO2 making up the dominant fraction (83 %) on low radiant-flux days, as its concentrations are still high. As most ClOVOCs appear to be formed photochemically, they exhibit a similar dependence on photolysis, contributing 3 % of the Cl radical budget observed here.

Effect of chlorine on cultivability of Shiga toxin producing Escherichia coli (STEC) and β-lactamase genes carrying E. coli and Pseudomonas aeruginosa

The worldwide spread of toxin-producing and multi-drug resistant bacteria in water, food and the environment is considered a major threat to human health. Drinking water quality is controlled by inspection of fecal indicators presence whereby viable contaminants will be efficiently reduced by chlorination which is a common process for disinfection. However, the all-out efficiency is arguable, because bacterial regrowth has been documented after disinfection. In this study, we investigated the stability of Shiga toxin producing Escherichia coli (STEC) and β-lactamase expressing E. coli and Pseudomonas aeruginosa isolates, both equipped with multiple or single β-lactamase resistance genes. The aim of the study was to analyze the efficiency of chlorine (Cl2) disinfection against shigatoxigenic or β-lactamase producing bacteria. Cl2 reacts with the bacterial cells after first contact. Counts of antibiotic resistant E. coli were lower after short than upon extended Cl2 treatment. P. aeruginosa counts decreased moderately upon 15–60 min treatment with 1.2 mg Cl2/l, while cells adapted to tap water were not cultivable anymore. We assume that the bacterial physiology changed to a temporary non-cultivatable state at first Cl2 contact followed by resuscitation of some cells at later stages. STEC viability went down continuously at low Cl2 concentrations and these toxigenic E. coli isolates exhibited slightly increased stability to Cl2 treatment compared with non-toxigenic E. coli. Controlling the efficiency of disinfection, realistic counts of cultivatable cells are achieved after extended Cl2 action.

High Levels of Daytime Molecular Chlorine and Nitryl Chloride at a Rural Site on the North China Plain.

Molecular chlorine (Cl2) and nitryl chloride (ClNO2) concentrations were measured using chemical ionization mass spectrometry at a rural site over the North China Plain during June 2014. High levels of daytime Cl2 up to ∼450 pptv were observed. The average diurnal Cl2 mixing ratios showed a maximum around noon at ∼100 pptv. ClNO2 exhibited a strong diurnal variation with early morning maxima reaching ppbv levels and afternoon minima sustained above 60 pptv. A moderate correlation (R2 = 0.31) between Cl2 and sulfur dioxide was observed, perhaps indicating a role for power plant emissions in the generation of the observed chlorine. We also observed a strong correlation (R2 = 0.83) between daytime (10:00-20:00) Cl2 and ClNO2, which implies that both of them were formed from a similar mechanism. In addition, Cl2 production is likely associated with a photochemical mechanism as Cl2 concentrations varied with ozone (O3) levels. The impact of Cl2 and ClNO2 as Cl atom sources is investigated using a photochemical box model. We estimated that the produced Cl atoms oxidized slightly more alkanes than OH radicals and enhanced the daily concentrations of peroxy radicals by 15% and the O3 production rate by 19%.

The formation of nickel(II) chloride ammine complexes in the pores of modified fibers of cellulose cloth

A sorbent was synthesized as a cellulose cloth, the fibers of which have nanopores with walls made of cellulose chains and ethanol cyclams. The formation of (NH4)2[NiL(NH3)2Cl2] complexes where L2– is the CH–(O–)–CH–(O–) glucopyranose group was established by chemical analysis and IR and UV/Vis spectroscopy. Using small-angle X-ray scattering and measurement of the partial free space and adsorption capacity, the complex formation in the [Ni(NH3)6]Cl2 concentration range of up to 0.43 mol/L was found to occur in nanopores with the sorption constant Ksorb = 15.8. The limiting content of the complexes is 2.63 mmol/g and their effective radius is 0.45 nm. In the concentration range of 0.43–0.91 mol/L, the complexation occurs on the fiber surface, Ksorb = 1.85. The effective radius of the complexes is 0.5 nm.

Using the Novel Method of Nonthermal Plasma To Add Cl Active Sites on Activated Carbon for Removal of Mercury from Flue Gas.

A new method using nonthermal plasma to add Cl active sites on activated carbon was proposed to improve the efficiency of activated carbon (AC) for removal of mercury from flue gas. The experiments were conducted via a lab-scale dielectric barrier discharge nonthermal plasma system and a vertical adsorption reactor. The results showed that the nonthermal plasma treatment with a small amount of Cl2 successfully added Cl active sites on AC and greatly increased the mercury removal efficiency of AC by chemisorption in a very short treatment time. The increase in Cl2 concentration for AC treatment promoted the efficiency of AC. The capacity of mercury adsorption positively correlated with the content of Cl2 for AC treatment, which depends on the number of Cl active sites on activated carbon. The treated AC maintained a high mercury removal efficiency within a temperature range of 30-210 °C. SO2 and H2O in flue gas inhibited the removal of mercury by AC, while HCl had a promotional effect. Scanning electron microscopy and X-ray photoelectron spectroscopy analysis indicated the chemisorption of mercury was attributed to the C-Cl groups generated on AC surfaces during Cl2 nonthermal plasma treatment. The C-Cl groups as active sites had strong adsorption energy for mercury, which converted elemental mercury to HgCl2.

Highly anisotropic etching of Ta thin films using high density plasmas of halogen based gases

Inductively coupled plasma reactive ion etching of Ta thin films masked with photoresist was performed using C2F6/Ar, HBr/Ar and Cl2/Ar gases. The etch characteristics such as etch rate, etch selectivity and etch profile were investigated in different gas concentrations of each gas. The Cl2 chemistry showed high degree of anisotropy in etch profile as well as fastest etch rate and highest etch selectivity of Ta films among these gases. Optical emission spectroscopy revealed that the increase in chlorine radicals with increasing Cl2 concentration was responsible for the increase in the Ta etch rate. The etch rate of Ta films increased with increasing ICP rf power and dc-bias voltage, and decreasing process pressure. Good etch profiles were obtained at high rf power and dc-bias voltage, and low process pressure. X-ray photoelectron spectroscopy confirmed the existence of a chemical reaction of Ta with chlorine radicals by forming tantalum chlorides. These results suggested that Ta etching in Cl2/Ar follows the typical reactive ion etching mechanism. It was concluded that a high degree of anisotropy and high etch rate of Ta films were achieved using Cl2/Ar gas.

Solid-state synthesis strategy of ZnO nanoparticles for the rapid detection of hazardous Cl2

In the present study, rapid and highly efficient solid-state synthesis strategy has been successfully employed for the synthesis of zinc oxide nanoparticles (ZnO NPs). Herein, prepared ZnO NPs are characterized and used for the fabrication of highly sensitive, selective, and accountable gas sensors. Structural elucidation, surface composition, and morphological investigations of as-synthesized ZnO NPs respectively, are carried out using X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, and selected area electron diffraction measurement techniques. The gas sensing properties of ZnO NPs studied at various operating temperatures and towards different oxidizing and reducing gases demonstrated the ability of ZnO to detect hazardous chlorine (Cl2) gas (optimum @ 200°C) with rapid response and recovery times. In addition, ZnO sensor film has detected the low 5ppm concentration of Cl2 with reasonable response of 199% with outstanding repeatability and stability in response. The variation of ZnO response with respect to different Cl2 concentrations has systematically been investigated and explored. Finally, the plausible sensing mechanism of ZnO with Cl2 gas molecules has been proposed using energy band model diagram.

Inland Concentrations of Cl2 and ClNO2 in Southeast Texas Suggest Chlorine Chemistry Significantly Contributes to Atmospheric Reactivity

Measurements of molecular chlorine (Cl2), nitryl chloride (ClNO2), and dinitrogen pentoxide (N2O5) were taken as part of the DISCOVER-AQ Texas 2013 campaign with a High Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) using iodide (I-) as a reagent ion. ClNO2 concentrations exceeding 50 ppt were regularly detected with peak concentrations typically occurring between 7:00 a.m. and 10:00 am. Hourly averaged Cl2 concentrations peaked daily between 3:00 p.m. and 4:00 p.m., with a 29-day average of 0.9 ± 0.3 (1σ) ppt. A day-time Cl2 source of up to 35 ppt∙h−1 is required to explain these observations, corresponding to a maximum chlorine radical (Cl•) production rate of 70 ppt∙h−1. Modeling of the Cl2 source suggests that it can enhance daily maximum O3 and RO2• concentrations by 8%–10% and 28%–50%, respectively. Modeling of observed ClNO2 assuming a well-mixed nocturnal boundary layer indicates O3 and RO2• enhancements of up to 2.1% and 38%, respectively, with a maximum impact in the early morning. These enhancements affect the formation of secondary organic aerosol and compliance with air quality standards for ozone and particulate matter.

Edge effects in second-harmonic generation in nanoscale layers of transition-metal dichalcogenides

The results of studying the optical properties of nanoscale single crystals of MoS2:Cl2 and WS2:Br2 semiconductor compounds are presented. In microscopic images obtained at the wavelength of the second (400 nm), edge effects are detected, which consist in enhancement or reduction in the second-harmonic signal intensity. Unlike previously proposed interference mechanisms of edge effects, non-interference mechanisms are considered. The occurrence of edge effects is associated with either an increased Cl2 and Br2 halogen molecule concentration or with an electrically induced second harmonic caused by band bending at the edges of individual crystal layers.

Light output enhancement of GaN-based light-emitting diodes by maskless surface roughening

In the present paper, the surface of GaN-based light-emitting diodes (LEDs) was roughened by inductively coupled plasma reactive ion etching (ICP-RIE) system. Without the utilization of etching mask, the roughened surface morphologies were optimized by varying Cl2 concentration in Cl2/BCl3/N2 mixing gas and adjusting RF bias power parameters of the ICP system. There was no obvious degradation of electrical properties of surface-roughened LEDs after the ICP dry etching process. Furthermore, the light output power of surface-roughened LEDs was enhanced by 43.2%, compared with conventional LEDs.

Etching mechanism of niobium in coaxial Ar/Cl2 radio frequency plasma

The understanding of the Ar/Cl2 plasma etching mechanism is crucial for the desired modification of inner surface of the three dimensional niobium (Nb) superconductive radio frequency cavities. Uniform mass removal in cylindrical shaped structures is a challenging task, because the etch rate varies along the direction of gas flow. The study is performed in the asymmetric coaxial RF discharge with two identical Nb rings acting as a part of the outer electrode. The dependence of etch rate uniformity on pressure, RF power, DC bias, Cl2 concentration, diameter of the inner electrode, temperature of the outer cylinder and position of the samples in the structure is determined. To understand the plasma etching mechanisms, we have studied several factors that have important influence on the etch rate and uniformity, which include the plasma sheath potential, Nb surface temperature, and the gas flow rate.

Inductive couple plasma reactive ion etching characteristics of TiO2 thin films

Changes in the inductively coupled plasma reactive ion etching characteristics of TiO2 thin films in response to the addition of HBr, Cl2 and C2F6 to Ar gas were investigated. As the HBr, Cl2 and C2F6 concentration increased, the etch rate increased; however, the etch profile degree of anisotropy followed a different trend. As HBr concentration increased, the greatest anisotropic etch profile was obtained at 100% HBr, while the greatest anisotropic etch profile was obtained at concentrations of 25% when etching was conducted under C2F6 and Cl2. Field emission scanning electron microscopy revealed that 25% C2F6 generated the greatest vertical etch profile; hence, etch parameters were varied at this concentration. The effects of rf power, dc-bias voltage and gas pressure on the etch rate and etch profile were also investigated. The etch rate and degree of anisotropy in the etch profile increased with increasing rf power and dc-bias voltage and decreasing gas pressure. X-ray photoelectron spectroscopy analysis of the films etched under a C2F6/Ar gas mixture revealed the existence of etch byproducts containing F (i.e. TiFx) over the film. CxFy compounds were not detected on the film surface, probably due to contamination with atmospheric carbon.

Room temperature ppb level Cl2 detection and sensing mechanism of highly selective and sensitive phthalocyanine nanowires

Nanowires of Cu(II) 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (CuPcOC4) have been fabricated onto the glass substrate by using low cost self-assembly technique. It has been demonstrated that these nanowires were highly sensitive and selective towards Cl2 at room temperature with minimum detection limit of 5 ppb. The response of nanowires was found to increase linearly (91–670%) with increase in Cl2 concentration (5–1500ppb). The adsorption of Cl2 on nanowires surface has followed Elovich equation. Raman spectroscopic and XPS studies revealed that central metal ions of CuPcOC4 molecules were the predominant sites of Cl2 absorption. The results emphasized that these nanowires can be promising candidates for room temperature Cl2 sensing applications.

Development of statistical models for trihalomethane (THM) occurrence in a water distribution network in Central Thailand

This study initially investigated the occurrence of trihalomethanes (THMs) in the water supply system of Metropolitan Bangkok, Thailand, evaluating 624 samples collected between 2007 and 2009. It was found that the mean total THM concentration was 66 μg/L, with CHCl3 accounting for 85% of the total. The main focus, however, was the development of models using linear and non-linear regression analyses to determine the effect of key disinfection parameters on THM formation. Regression techniques revealed that the total and residual Cl2 concentrations, and contact time (expressed as the equivalent pipe distance) played the most critical role in THM formation, regardless of the season investigated. A moderate correlation was generally observed, however, the correlation was considerably stronger in the dry seasons (i.e. winter and summer) compared to the rainy season. Furthermore, the similarity in statistical parameters regarding the actual and predicted THM concentrations suggests that the models developed are reliable.

Influence of the chlorine concentration on the radiation efficiency of a XeCl exciplex lamp

The influence of the chlorine concentration on the radiation efficiency of coaxial exciplex lamps (excilamps) excited by a dielectric barrier discharge (DBD) in binary Xe-Cl2 mixtures at pressures of 240–250 Torr is investigated experimentally and theoretically. The experiments were carried out at Cl2 concentrations in the range of 0.01–1%. The DBD characteristics were calculated in the framework of a one-dimensional hydrodynamic model at Cl2 concentrations in the range of 0.1–5%. It is found that the radiation intensities of the emission bands of Xe*2(172 nm) and XeCl* (308 nm) are comparable when the chlorine concentration in the mixture is in the range of 0.01–0.1%. In this case, in the mixture, the radiation intensity of the Xe*2 molecule rapidly decreases with increasing Cl2 concentration and, at a chlorine concentration of ≥0.2%, the radiation of the B → X band of XeCl* molecules with a peak at 308 nm dominates in the discharge radiation. The radiation efficiency of this band reaches its maximum value at chlorine concentrations in the range of 0.4–0.5%. The calculated efficiencies of DBD radiation exceed those obtained experimentally. This is due to limitations of the one-dimensional model, which assumes the discharge to be uniform in the transverse direction, whereas the actual excilamp discharge is highly inhomogeneous. The influence of the chlorine concentration on the properties of the DBD plasma in binary Xe-Cl2 mixtures is studied numerically. It is shown that an increase in the Cl2 concentration in the mixture leads to the attachment of electrons to chlorine atoms and a decrease in the electron density and discharge conductivity. As a result, the electric field and the voltage drop across the discharge gap increase, which, in turn, leads to an increase in the average electron energy and the probability of dissociation of Cl2 molecules and ionization of Xe atoms and Cl2 molecules. The total energy deposited in the discharge rises with increasing chlorine concentration due to an increase in the power spent on the heating of positive and negative ions. The power dissipated by electrons decreases with increasing chlorine concentration in the working mixture. Recommendations on the choice of the chlorine content in the mixture for reducing the intensity of VUV radiation of the second continuum of the Xe*2 excimer without a substantial decrease in the excilamp efficiency are formulated.

Inactivation of <i>Cryptosporidium</i> and <i>Giardia</i> by Chlorine in Water

In order to study the effect of chlorine (Cl2) inactivating Cryptosporidium and Giardia in water, different factors as Cl2 concentration, contact time, pH, temperature, turbidity and organic content which might influence the inactivation were studied by using fluorescence staining method. With the Cryptosporidium and Giardia was 1×106 cysts/mL, turbidity 1.0NTU, temperature 22°C, pH 7.0, and after 280 min reaction, under the condition that the Cl2 concentrations was 8.0mg/L, the inactivation ratio could be more than 99%. With increases in turbidity, the inactivating effect decreased. If the inactivating time achieved 360 min, it could meet the presetting inactivation ratio with turbidity 0.1~10.0 NTU. The inactivating capability of Cl2 was found to be stronger under acidic than that under alkalic conditions. Inactivation rate improves with a temperature increase from 5 to 25°C, but decreases beyond this.

Physiological and biochemical responses of the marine dinoflagellate Prorocentrum minimum exposed to the oxidizing biocide chlorine

Toxic effects of the commonly used biocide chlorine (Cl2) on the marine dinoflagellate Prorocentrum minimum were assessed using growth-, pigment- and enzyme activity-based endpoints. Cell count, chlorophyll a levels, carotenoids, and chlorophyll autofluorescence were monitored up to 72h after exposure to Cl2, and these parameters showed a dose- and time-dependent decrease. The 72-h median effective concentration (EC50) based on growth rate was 1.177mgL−1. Cl2 dose above 0.5mgL−1 were toxic to P. minimum after 6-h exposure to Cl2; the effect increased with increase in exposure time as revealed by a significant reduction in growth rate and decreased chlorophyll fluorescence. Moreover, the activities of antioxidant enzymes, including superoxide dismutase and catalase, were altered proportionally with increasing Cl2 dose. The results of this study show that Cl2 concentrations as observed in power-plant discharges and in drinking-water systems cause physiological and biochemical damage to the microalgae.

Plasma Chemical and Electrical Modeling of a Dielectric Barrier Discharge in Kr–Cl2 Gas Mixtures

This paper reports the study of the Kr–Cl2 plasma chemistry in terms of the homogenous model of a dielectric barrier discharge and for two kinds of the applied voltage excitation shape. The effect of Cl2 concentration in the gas mixture, as well as gas pressure and power frequency on the discharge efficiency and the 222 nm photon generation, under typical experimental operating conditions, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to ultraviolet emission in the lamp is in the range of 4.4–12 %, and it will be very affected at high chlorine percentage (>1 %) and high gas pressure (>200 Torr). A comparison between the sinusoidal and the burst excitation waveforms reveals that the burst excitation method provides an enhanced light source performance compared to the sinusoidal wave.

Nitryl Chloride and Molecular Chlorine in the Coastal Marine Boundary Layer

The magnitude and sources of chlorine atoms in marine air remain highly uncertain but have potentially important consequences for air quality in polluted coastal regions. We made continuous measurements of ambient ClNO(2) and Cl(2) concentrations from May 15 to June 8 aboard the Research Vessel Atlantis during the CalNex 2010 field study. In the Los Angeles region, ClNO(2) was more ubiquitous than Cl(2) during most nights of the study period. ClNO(2) and Cl(2) ranged from detection limits at midday to campaign maximum values at night reaching 2100 and 200 pptv, respectively. The maxima were observed in Santa Monica Bay when sampling the Los Angeles urban plume. Cl(2) at times appeared well correlated with ClNO(2), but at other times, there was little to no correlation implying distinct and varying sources. Well-confined Cl(2) plumes were observed, largely independent of ClNO(2), providing support for localized industrial emissions of reactive chlorine. Observations of ClNO(2), Cl(2), and HCl are used to constrain a simple box model that predicts their relative importance as chlorine atom sources in the polluted marine boundary layer. In contrast to the emphasis in previous studies, ClNO(2) and HCl are dominant primary chlorine atom sources for the Los Angeles basin.

NASICON-based potentiometric Cl2 sensor combining NASICON with Cr2O3 sensing electrode

This work focuses on the sensing performance of the sensor to chlorine (Cl2) gas in air based on sodium super ionic conductor (NASICON) and oxide electrode. Among eight single oxides examined, Cr2O3 exhibited the highest sensitivity to Cl2 gas in air at 300°C. ΔEMF values of the sensing device attached with Cr2O3 changed linearly with the logarithm of Cl2 concentration in the range of 5–50ppm. The sensitivity of the sensors was testified by using Cr2O3 electrode sintered with different temperature. The sensor using Cr2O3 sintered at 600°C showed the largest sensitivity to Cl2 at 300°C. Through burying the reference electrode in middle of the NASICON layer and decreasing the area of the reference electrode, the sensitivity of the sensor to Cl2 can be greatly improved. Finally, a sensing mechanism related to the mixed potential was proposed for the sensor based on NASICON and oxide electrode.