Cl2 Concentration Research Articles

Application of sodium hypochlorite for human norovirus and hepatitis A virus inactivation in groundwater.

In this study, the effect of sodium hypochlorite (10-200 ppm of Cl2) on the inactivation of human norovirus (HuNV) GII.4 and hepatitis A virus (HAV) in groundwater was investigated using propidium monoazide (PMA)/reverse transcription quantitative real-time PCR (RT-qPCR). Initially, 4.00 log10 genome copies/μL of HuNV GII.4 or 5.50 log10 genome copies/μL of HAV were artificially inoculated in groundwater. The titers of HuNV GII.4 and HAV decreased significantly (P < 0.05) with increasing Cl2 concentrations. Groundwater was treated with 10, 30, 50, 100, 150, and 200 ppm of Cl2, and the viable HuNV GII.4 was significantly (P < 0.05) reduced to 3.28 (0.21-log reduction), 3.18 (0.31-log reduction), 3.01 (0.48 log reduction), 2.75 (0.74 log reduction), 2.54 (0.95 log reduction), and 2.34 (1.15 log reduction) log10 genome copies/μL, respectively. The viable HAV was also significantly (P < 0.05) reduced to 4.99 (0.23 log reduction), 4.76 (0.46 log reduction), 4.55 (0.67 log reduction), 4.21 (1.01-log reduction), 3.89 (1.33 log reduction), and 3.64 (1.58 log reduction) log10 genome copies/μL, respectively. The decimal reduction times (D values) (1-log10 genome reduction) of HuNV GII.4 and HAV infectivity in groundwater were predicted as 116.7 and 98.9 ppm of Cl2, respectively, using the first-order kinetics model (HuNV GII.4: y = -0.0054x + 3.3585, correlation coefficient (R2) = 0.97; HAV: y = -0.0091x + 5.0470, R2 = 0.97). The result specifically suggests that 150- to 200-ppm Cl2 can potentially be used for the inactivation of >1-log10 genome copy/μL HuNV GII.4 and HAV in groundwater.IMPORTANCEGroundwater represents a vital component of the global water supply, serving as a crucial source of potable water for humans. It serves as a source of potable water for up to 50% of the global population and accounts for 43% of all water used for irrigation. It thus follows that the sustainable management of groundwater represents a pivotal solution. However, the regrowth of pathogens in water that is not treated with chlorine or where proper residual chlorine is not maintained represents a risk to public health.

Dose and gender dependence of chlorine inhalation in a conscious ovine model

Characterization of the pathophysiology of ARDS following chlorine gas inhalation in clinically relevant translational large animal models is essential, as the opportunity for clinical trials in this type of trauma is extremely limited. To investigate Cl2 concentration and gender-dependent ARDS severity. Sheep (n = 54) were exposed to air or Cl2 premixed in air at a concentration of 50, 100, 200, and 300 ppm for 30 min under anesthesia/analgesia and monitored for an additional 48 h in a conscious state. Cardiopulmonary variables and survival endpoints were compared between male and female sheep. Overall there were no significant differences in the responses of female and male sheep except pulmonary oxygenation tended to be better in the male sheep (300 ppm group), and the pulmonary arterial pressure was lower (200 ppm group). The onset of mild ARDS (200 < PaO2/FiO2 ≤ 300) was observed at 36 h post exposure in the 50 ppm group, whereas the 100 ppm group developed mild and moderate (100 ≤ PaO2/FiO2 ≤ 200) ARDS by 12 and 36 h after injury, respectively. The 200 ppm and 300 ppm groups developed moderate ARDS within 6 and 3 h after injury, respectively. The 300 ppm group progressed to severe (PaO2/FiO2 ≤ 100) ARDS at 18 h after injury. Increases in pPeak and pPlateau were noted in all injured animals. Compared to sham, inhalation of 200 ppm and 300 ppm Cl2 significantly increased lung extravascular water content. The thoracic cavity fluid accumulation dose-dependently increased with the severity of trauma as compared to sham. At necropsy, the lungs were red, heavy, solidified, and fluid filled; the injury severity grew with increasing Cl2 concentration. The severity of ARDS and mortality rate directly correlated to inhaled Cl2 concentrations. No significant sex-dependent differences were found in measured endpoint variables.

Chlorine Decay Simulation in Real Water Distribution System Using Epanet Program

Abstract Deterioration of treated drinking water intended for consumption during distribution may be due to physical, chemical or microbiological changes that occur in the water. In addition, the type of pipe material and disintegration of a disinfectant agent can affect the quality of the water supplied. Therefore, the research approach is to simulate the decay residual Cl2 through potable water distribution networks produced by a desalination plant of Oran city in western Algeria. EPANET 2.0 software was used for estimating and predicting Cl2 concentration at different water network points. The value of bulk flow decay coefficient (Kb) is set to −1,99 day−1 for a 50-year-old steel pipe, value for the wall decay coefficient (Kw) was determined using a trial-and-error procedure and assumed to be −1,2 day−1. An efficient model with an extended simulations period of 72 h can plot spatial and temporal variations of residual Cl2 concentrations at all links and nodes. Cl2 is injected at the El Mactaa desalination plant, with a concentration of 0.6 mg/l permanently. As well, it was observed that 51.33% of the Cl2 loss is due to pipe wall reaction, while 42.34 and 6.33% represent the bulk and tank reactions respectively. The results show that the range of residual Cl2 (0.11-0,45 mg/l) and most of the measured values are less than are below the minimum authorized threshold (0.2 – 0.5 mg/l) WHO standard. Therefore, it is recommended to rehabilitate the old water transfer pipes and re-chlorination stations were necessary to add into network. Statistical analysis shows that the calculated results correspond well to the observed data. EPANET can follow the Cl2 concentration in the drinking water network produced by El Mactaa desalination plant. It is a research tool to improve our understanding of water movement in the distribution system.

Labeled free electrochemiluminescence aptamer platform based on one-step cathodic electrochemical growth of 2D/3D Ru-BTC-MOFs nanoparticles to detect carcinoembryonic antigen

[Ru(dcbpy)3]2+ functionalized 2D/3D hybrid metal–organic frameworks (Ru-BTC-MOFs), which performed good ECL performance, were synthesized by on one-step cathodic electrodeposition with Zn(NO3)2 as metal ion source, Ru(dcbpy)3Cl2) (tri(4,4-dicarboxybipyridine) ruthenium chloride) and H3BTC (1,3,5-phenyl tricarboxylic acid) as organic ligand. The effect of electrodeposition voltage, electrodeposition time, H3BTC and [Ru(dcbpy)3]Cl2 concentration on the morphology and ECL performance of Ru-BTC-MOFs were investigated in detail. An ECL biosensor platform for sensitive detection of carcinoembryonic antigen (CEA) was constructed by further modified AuNPs and aptamer on the Ru-BTC-MOFs/GCE. The specifically recognition and adsorption of CEA would hinder the electron transfer between Ru-BTC-MOFs and trinpropylamine (TPA) as the co-reactive agent, resulting in decreasing the ECL intensity. Under the optimal experimental conditions, the ECL intensity and logarithm of CEA concentration showed a good linear relationship in the concentration range of 10.0 fg/mL to 10.0 ng/mL, and the detection limit was 5.56 fg/mL. The proposed sensor performed acceptable reproducibility, repeatability, anti-interference ability and stability, and it would be expected to have broad application prospects in clinical trials.

Mechanistic insight into the role of typical microplastics in chlorination disinfection: Precursors and adsorbents of both MP-DOM and DBPs

Microplastics (MPs) in drinking water are predominantly < 10 µm. The leaching of MPs derived dissolved organic matters (MP-DOM) from 5 µm polypropylene MPs (PP-MPs) and polystyrene MPs (PS-MPs) and the formation of MP-DOM derived disinfection byproducts during chlorination disinfection were first investigated. Comparably, PS-MPs are more vulnerable to chlorination and the primary attacks are on para C in aromatic side-chains via electrophilic Cl-substitution and oxidation by two-electron transfer. The O/C and Cl/C ratio of polystyrene MPs was linear and exponential versus initial available Cl2 concentrations, respectively. The significant PS-DOM leaching was observed with initial available Cl2 of 4.0 mg/L (USEPA recommended upper dose). As the initial available Cl2 concentration increased to 8.0 mg/L, the adsorption of chloro-phenolic-components of 200 Daltons in PS-DOM by 5 µm PS-MPs was observed for the first time. Trichloromethane (TCM) was identified as the dominant disinfection byproduct with a formation potential of 60.3 ± 7.8 and 73.7 ± 9.8 μg/mg for PS-DOM and PP-DOM, respectively. The derived TCM could adsorb onto PS-MPs followed the pseudo-second-order kinetic and Langmuir isotherm models. Extreme chlorination could reduce the maximal adsorption capacity of TCM on 5 µm PS-MPs from 196.68 ± 48.66 to 146.02 ± 32.98 μg/g. Thus, PS-MPs act as precursors and carriers of TCM in chlorination.

High Chlorine Concentrations in an Unconventional Oil and Gas Development Region and Impacts on Atmospheric Chemistry.

Growth in unconventional oil and gas development (UOGD) in the United States has increased airborne emissions, raising environmental and human health concerns. To assess the potential impacts on air quality, we deployed instrumentation in Karnes City, Texas, a rural area in the middle of the Eagle Ford Shale. We measured several episodes of elevated Cl2 levels, reaching maximum hourly averages of 800 ppt, the highest inland Cl2 concentration reported to date. Concentrations peak during the day, suggesting a strong local source (given the short photolysis lifetime of Cl2) and/or a photoinitiated production mechanism. Well preproduction activity near the measurement site is a plausible source of these high Cl2 levels via direct emission and photoactive chemistry. ClNO2 is also observed, but it peaks overnight, consistent with well-known nocturnal formation processes. Observations of organochlorines in the gas and particle phases reflect the contribution of chlorine chemistry to the formation of secondary pollutants in the area. Box modeling results suggest that the formation of ozone at this location is influenced by chlorine chemistry. These results suggest that UOGD can be an important source of reactive chlorine in the atmosphere, impacting radical budgets and the formation of secondary pollutants in these regions.

A paired emitter–detector diode-based photometer for the determination of sodium hypochlorite adulteration in milk

This paper reports on developing a low cost but efficient paired emitter–detector diode (PEDD)-based photometer. The photometer consists of a white light-emitting diode (LED) as the emitter diode, an RGB LED as the detector diode, and a multimeter for recoding the signal. The developed PEDD-based photometer was utilized for the determination of liquid bleach adulteration in cow milk samples. N,N-Diethyl-p-phenylenediamine sulfate aqueous solution of pH 6 was used as a probe to monitor the presence of residual active chlorine in milk. The results showed that the developed method could be used to determine sodium hypochlorite in the concentration range of 0.5 to 20.0 ppm Cl2 with 0.14 and 0.46 ppm Cl2 limit of detection and limit of quantification, respectively. The intraday and interday precisions of the method at two concentration levels of 5.5 and 13.7 ppm Cl2 were 1.04% and 0.52%, and 1.81% and 1.02%, respectively. The recoveries of 114.2% and 106.9% were obtained for 5.5 and 13.7 ppm Cl2 concentrations levels, respectively. Real sample analyzes results showed that “maybe” liquid bleach adulteration in milk is the case for local distributors of raw milk.

Formation of Dichlorine Monoxide for Organic Pollutant Degradation by Free Chlorine in High Chloride-Containing Water

Several ppm levels of free chlorine in high chloride-containing water of no less than 0.20 M show remarkably high degradation rate constants toward carbamazepine (kCBZ′). Dichlorine monoxide (Cl2O) was identified to be responsible for the high kCBZ′. Cl2O degrades aromatic pollutants connected to more electron-donating functional groups faster when comparing kCl2O to 1,4-dimethoxybenzene, bisphenol A, benzoic acid, and CBZ. However, its formation at low free chlorine levels in high chloride-containing water cannot be explained by our current knowledge. We proposed an alternative Cl2O formation mechanism, in which chloride transforms hypochlorous acid/hypochlorite (HOCl/ClO–) to dichlorine (Cl2) and polychloride monoanions (Cln–), which then react with HOCl/ClO– to form Cl2O. Decreasing pH from 8.60 to 4.33 increases Cl2 concentrations and thus generates about 600× higher Cl2O concentrations. Weak acid anions, for example, phosphate and bicarbonate, are strong nucleophiles assisting the Cl2O hydrolysis, but their presence at the testing conditions does not much affect kCBZ′. The proposed alternative Cl2O formation mechanism reveals the roles of chloride in shifting the equilibrium toward the Cl2O formation, allowing the simple chlorine addition strategy to degrade recalcitrant organic pollutants in high chloride-containing wastewater. It may also change our understanding of the speciation of different free chlorine species and their impacts on the DBP formation in high chloride-containing wastewater.

Tailoring the performance of phthalocyanine-based sensor: Side chain substitution and nanofabrication

Room temperature Cl2 sensing properties of chemiresistive gas sensor based on Zinc Phthalocyanine (ZnPc) were improved by functionalizing ZnPc molecule with peripheral substitution of alkoxy side chains. The chemiresistive sensors of substituted ZnPc (ZnPcOC8) were made using spin-coated films and solution-processed nanostructures. These sensors were highly selective and sensitive towards Cl2 as compared to NH3, NO and NO2. The chlorine response kinetics of ZnPc and substituted ZnPcOC8-based sensors were investigated for Cl2 concentration range 5–1500 ppb. The ZnPcOC8-based sensors exhibit a limit of 5 ppb Cl2 with faster sensing kinetics as compared to ZnPc-based sensor. Among the three sensors, the solution-processed nanostructured-based sensor exhibits the best performance. The gas sensing mechanism of sensors has been investigated by XPS, suggesting that Zn+2 were the preferred sites for Cl2 interaction. These investigations suggest that alkoxy substitution on phthalocyanine molecules leads to development of cost effective and highly sensitive chlorine gas sensors.

(Digital Presentation) Silver Electrode Potentials in NaCl–KCl–Cscl Eutectic Melts

Molten salts have a number of potential applications including metals’ electrowinning and electrorefining, pyrochemical spent nuclear fuels’ reprocessing. Considerable efforts were devoted over decades to investigation of various electrochemical processes in molten salts, especially in fused chlorides. Silver chloride electrode is one of convenient types of reference electrodes often employed in potentiometry measurements. This electrode has several advantages (especially compactness) compare to the standard chlorine reference electrode, potential of which in chloride melts is taken as zero. Surprisingly little attention was paid so far to the systematic study (covering the effect of temperature and concentration) of silver electrode potentials in molten chlorides, with majority of the works dating back to 1950-s and 60-s. Molten LiCl–KCl eutectic was, on obvious reasons, the best studied, and several other melts (NaCl, NaCl–KCl, LiCl–KCl–CsCl, NaCl–CsCl) were also looked at.The present study was directed at the systematic study of silver electrochemistry in fused alkali chlorides and determining silver electrode potentials. Here we present the results of the experiments performed in the melts based on the ternary NaCl–KCl–CsCl (30–24.5–45.5 mol. %) eutectic mixture at 823–1073 K. Electrode potentials of silver were determined using the electromotive force measurements method and the following galvanic cell:Ag|(NaCl–KCl–CsCl)+AgCl||(NaCl–KC1–CsCl)|Cl2 (C)Concentration of silver in the electrolyte varied from 0.1 to 5 wt. %.Silver electrode quickly equilibrated with the electrolyte and the potential remained stable over long time, Figure. Experimentally obtained electrode potentials were then used to calculate silver formal standard electrode potentials.Figure. An example of silver electrode potential evolution over time in (NaCl–KCl–CsCl)–AgCl (5 wt. %) melt at 823 K. 2Cl–/Cl2 reference electrode. Figure 1

Sensing Gas Mixtures by Analyzing the Spatiotemporal Optical Responses of Liquid Crystals Using 3D Convolutional Neural Networks.

We report how analysis of the spatial and temporal optical responses of liquid crystal (LC) films to targeted gases, when performed using a machine learning methodology, can advance the sensing of gas mixtures and provide important insights into the physical processes that underlie the sensor response. We develop the methodology using O3 and Cl2 mixtures (representative of an important class of analytes) and LCs supported on metal perchlorate-decorated surfaces as a model system. Although O3 and Cl2 both diffuse through LC films and undergo redox reactions with the supporting metal perchlorate surfaces to generate similar initial and final optical states of the LCs, we show that a three-dimensional convolutional neural network can extract feature information that is encoded in the spatiotemporal color patterns of the LCs to detect the presence of both O3 and Cl2 species in mixtures and to quantify their concentrations. Our analysis reveals that O3 detection is driven by the transition time over which the brightness of the LC changes, while Cl2 detection is driven by color fluctuations that develop late in the optical response of the LC. We also show that we can detect the presence of Cl2 even when the concentration of O3 is orders of magnitude greater than the Cl2 concentration. The proposed methodology is generalizable to a wide range of analytes, reactive surfaces, and LCs and has the potential to advance the design of portable LC monitoring devices (e.g., wearable devices) for analyzing gas mixtures using spatiotemporal color fluctuations.

Photodissociation of particulate nitrate as a source of daytime tropospheric Cl2

Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl2), a Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl2 concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl2 (2.7 pptv s−1 at noon). Field and laboratory experiments indicate that photodissociation of particulate nitrate by sunlight under acidic conditions (pH < 3.0) can activate chloride and account for the observed daytime Cl2 production. The high Cl2 concentrations significantly increased atmospheric oxidation. Given the ubiquitous existence of chloride, nitrate, and acidic aerosols, we propose that nitrate photolysis is a significant daytime chlorine source globally. This so far unaccounted for source of chlorine can have substantial impacts on atmospheric chemistry.

Corrosion of SiC-coated graphite susceptor by NH3 and Cl2

This study aims to investigate the corrosion of a SiC-coated graphite susceptor using NH3 and Cl2 in an epitaxial growth environment. The corrosion performance of NH3 with graphite and SiC-coated graphite was investigated through microstructure characterization and mass loss rate changes in detail. Gaseous NH3 had a high corrosion rate on the graphite substrate, but hardly reacted with the SiC coating. Additionally, analyses of the tested samples revealed that Cl2 gas corroded the SiC coating at high temperatures and formed many corrosion holes and residual free carbon on the surface. As the Cl2 concentration increased, the corrosion depth gradually increased. Further experiments on commercial SiC-coated graphite susceptors showed that Cl2 preferentially corroded the grain boundaries of the SiC coating, and then the grains were corroded, resulting in a decrease in the coating strength until cracking and failure.

Chlorine exposure induces Caspase-3 independent cell death in human lung epithelial cells

Chlorine (Cl2) is a common toxic industrial gas and human inhalation exposure causes tissue damage with symptoms ranging from wheezing to more severe symptoms such as lung injury or even death. Because the mechanism behind Cl2-induced cell death is not clearly understood, the present study aimed to study the cellular effects in vitro after Cl2 exposure of human A549 lung epithelial cells. In addition, the possible treatment effects of the anti-inflammatory antioxidant N-acetyl cysteine (NAC) were evaluated.Exposure of A549 cells to Cl2 (100–1000 ppm) in the cell medium induced cell damage and toxicity within 1 h in a dose-dependent manner. The results showed that 250 ppm Cl2 increased cell death and formation of apoptotic-like bodies, while 500 ppm Cl2 exposure resulted in predominantly necrotic death. Pre-treatment with NAC was efficient to prevent cell damage at lower Cl2 concentrations in part by averting the formation of apoptotic-like bodies and increasing the expression of the anti-apoptotic proteins clusterin and phosphorylated tumour protein p53(S46). Analysis showed that Cl2 induced cell death by a possibly caspase-independent mechanism, since no cleavage of caspase-3 could be detected after exposure to 250 ppm. Currently, these results justifies further research into new treatment strategies for Cl2-induced lung injury.

Role of Carbonate Species on General Acid Catalysis of Bromide Oxidation by Hypochlorous Acid (HOCl) and Oxidation by Molecular Chlorine (Cl2).

Kinetic models for disinfectant decay and disinfection byproduct (DBP) formation are necessary for predicting water quality from the treatment plant to the tap. A kinetic model for conditions relevant to chloramine disinfection of drinking water (pH 6-9 and carbonate-buffered) was developed to simulate incomplete bromide (Br-) oxidation during short prechlorination periods because it is the first step in a complex system of reactions that leads to disinfectant loss and DBP formation. Hypochlorous acid and molecular chlorine were the free chlorine species relevant to Br- oxidation, and Cl2 hydrolysis and formation reactions were necessary to accurately simulate Cl2 concentrations instead of assuming equilibrium. Previous work has shown that Br- oxidation by HOCl and Cl2 formation are acid-catalyzed and Cl2 hydrolysis is base-catalyzed, but the impact of carbonate species had not been studied. This work showed that the carbonate species have an enhanced catalytic impact with rate constants up to 1000 times larger than would be estimated by the Brønsted relationship for similar acids, which causes the oxidation by HOCl rate constant (kHOCl) to nearly double and oxidation by Cl2 to occur above pH 7 in high-alkalinity waters.

Histone H4 aggravates inflammatory injury through TLR4 in chlorine gas-induced acute respiratory distress syndrome

BackgroundChlorine gas (Cl2) exposure remains a public health concern in household, occupational, and transportation accidents around the world. The death rate associated with acute respiratory distress syndrome (ARDS) caused by high concentrations of Cl2 is very high, mainly because the pathogenesis of ARDS remains unclear. Histone H4 has been identified as an important endogenous pro-inflammatory molecule. The present study aimed to examine the pathogenic role of histone H4 in Cl2-induced ARDS.MethodsARDS was induced by Cl2 exposure in male C57BL/6 mice. Circulating histone H4, blood gas, pulmonary edema, endothelial activation, and neutrophil infiltration were measured during acute lung injury (ALI). Histone H4 or anti-H4 antibody was administered through the tail vein 1 h prior to Cl2 exposure to study the pathogenic role of histone H4. Toll-like receptor 2 knock-out (Tlr2-KO) and Tlr4-KO mice were used in conjunction with blocking antibody against TLR1, TLR2, TLR4, or TLR6 to explore the mechanism involved in histone H4-mediated injury.ResultsCl2 exposure induced a concentration-dependent ALI. The levels of circulating histone H4 were positively correlated with Cl2 concentrations. Pretreatment with intravenous histone H4 further aggravated lethality rate, blood gas, endothelial activation, and neutrophil infiltration, while anti-H4 antibody showed protective effects. Tlr4 deficiency improved lethality rate, blood gas, and pulmonary edema, and prevented endothelial and neutrophil activation caused by Cl2 exposure. More importantly, Tlr4 gene deletion greatly diminished the effect of histone H4 or anti-H4 antibody observed in wild-type (WT) mice. The impact of Tlr2 on inflammatory injury was not significant. The role of TLRs was also validated by endothelial activation mediated by histone H4 in vitro.ConclusionsCirculating histone H4 played a pro-inflammatory role in ARDS caused by Cl2. TLR4 was closely involved in histone H4-mediated inflammatory injury. Therefore, intervention targeting histone H4 is potentially protective.

Reduction of biofouling potential in cartridge filter by using chlorine dioxide for enhancing anti-biofouling of seawater reverse osmosis membrane

In general, cartridge filters (CFs) are installed before reverse osmosis systems as a safeguard to minimize fouling of the reverse osmosis membrane in seawater desalination plants. Depending on the retention time of microorganisms and various fouling matter in the storage tank, pipe, and filter housing, serious fouling of the CF may occur, decreasing its lifetime. More importantly, biofouling of CFs in a continuous process can have a significant impact on reverse osmosis membrane fouling. Few studies related to CF fouling and control have been undertaken due to the low cost of CFs. Herein, comparative evaluation of optical density (O.D) for Cl2 and ClO2 was performed to investigate the efficiency of biofouling control and for developing alternative disinfection processes because the chemistry and reactivity of ClO2 differ from those of Cl2. The results showed that the concentrations of Cl2 and ClO2 required to achieve a log reduction value of 2 for the live bacterial cells with 180 min of contact time were 1.5 and 0.6 mg L−1, respectively. Both Cl2 and ClO2 were effective for the control of organic matter and particles. However, the required Cl2 concentration (1.5 mg L−1) was 2.5 times higher than that of ClO2 (0.6 mg L−1). Surface analysis and economic evaluation of the CF showed that ClO2 has higher biofouling control ability than Cl2 and is more economical, at a current cost of $ 23,667 during seawater desalination plant duration.

Observational Constraints on the Formation of Cl2 From the Reactive Uptake of ClNO2 on Aerosols in the Polluted Marine Boundary Layer

AbstractWe use observations from the 2015 Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign to constrain the proposed mechanism of Cl2 production from ClNO2 reaction in acidic particles. To reproduce Cl2 concentrations observed during WINTER with a chemical box model that includes ClNO2 reactive uptake to form Cl2, the model required the ClNO2 reaction probability, γ (ClNO2), to range from 6 × 10−6 to 7 × 10−5, with a mean value of 2.3 × 10−5 (±1.8 × 10−5). These field‐determined γ (ClNO2) are more than an order of magnitude lower than those determined in previous laboratory experiments on acidic surfaces, even when calculated particle pH is ≤2. We hypothesize this is because thick salt films in the laboratory enhanced the reactive uptake ClNO2 compared to that which would occur in submicron aerosol particles. Using the reacto‐diffusive length‐scale framework, we show that the field and laboratory observations can be reconciled if the net aqueous‐phase reaction rate constant for ClNO2 (aq) + Cl‐(aq) in acidic particles is on the order of 104 s−1. We show that wet particle diameter and particulate chloride mass together explain 90% of the observed variance in the box model‐derived γ (ClNO2), implying that the availability of chloride and particle volume limit the efficiency of the reaction. Despite a much lower conversion of ClNO2 into Cl2, this mechanism can still be responsible for the nocturnal formation of 10–20 pptv of Cl2 in polluted regions, yielding an atmospherically relevant concentration of Cl atoms the following morning.

Modeling the impact of heterogeneous reactions of chlorine on summertime nitrate formation in Beijing, China

Abstract. Comprehensive chlorine heterogeneous chemistry is incorporated into the Community Multiscale Air Quality (CMAQ) model to evaluate the impact of chlorine-related heterogeneous reaction on diurnal and nocturnal nitrate formation and quantify the nitrate formation from gas-to-particle partitioning of HNO3 and from different heterogeneous pathways. The results show that these heterogeneous reactions increase the atmospheric Cl2 and ClNO2 level (∼ 100 %), which further affects the nitrate formation. Sensitivity analyses of uptake coefficients show that the empirical uptake coefficient for the O3 heterogeneous reaction with chlorinated particles may lead to the large uncertainties in the predicted Cl2 and nitrate concentrations. The N2O5 uptake coefficient with particulate Cl− concentration dependence performs better in capturing the concentration of ClNO2 and nocturnal nitrate concentration. The reaction of OH and NO2 in the daytime increases the nitrate by ∼15 % when the heterogeneous chlorine chemistry is incorporated, resulting in more nitrate formation from HNO3 gas-to-particle partitioning. By contrast, the contribution of the heterogeneous reaction of N2O5 to nitrate concentrations decreases by about 27 % in the nighttime, when its reactions with chlorinated particles are considered. However, the generated gas-phase ClNO2 from the heterogeneous reaction of N2O5 and chlorine-containing particles further reacts with the particle surface to increase the nitrate by 6 %. In general, this study highlights the potential of significant underestimation of daytime concentrations and overestimation of nighttime nitrate concentrations for chemical transport models without proper chlorine chemistry in the gas and particle phases.

Analysis of a series of urban-scale chlorine dispersion experiments and implications on indoor health consequences

In the United States, industrial compounds are routinely transported by rail in pressurized vessels, often near urban areas. A rupture of a vessel, for example due to a derailment, can result in the rapid release of a liquid-aerosol-gas mixture. The health consequences of such a release, especially close to population centers, are not well understood. To address this question, a series of controlled experimental releases of pressurized chlorine (Cl2) was conducted at the Dugway Proving Ground (Dugway, Utah). Each trial consisted of the sudden breach of a tank containing at least 4,500 kg (kg) of pressurized liquid Cl2. In this paper, we report on measured Cl2 concentrations in three test structures downwind of the release. Based on these data, we estimate the indoor-outdoor exchange, transport through a multi-room structure, and the first-order loss rate due to reaction or sorption. This loss rate is particularly important for consequence assessment. For example, in a mobile office with a ventilation rate of about three air changes per hour, the reaction loss rate was approximately 2.5 h−1. This accounts for a nearly 20 percent reduction in toxic load to indoor occupants. Finally, the paper discusses the modeling and analysis of a typical urban hazard assessment.