Chlorine

About: Chlorine is a research topic. Over the lifetime, 20879 publications have been published within this topic receiving 254775 citations. The topic is also known as: Cl & element 17.

Unexpectedly high concentrations of molecular chlorine in coastal air

Abstract: The fate of many atmospheric trace species, including pollutants such as nitrogen oxides and some volatile organic compounds, is controlled by oxidation reactions In the daytime troposphere, these reactions are dominated by photochemically produced OH radicals; at night and in polluted environments, NO3 radicals are an important oxidant1 Ozone can contribute to the oxidation of atmospheric species during both day and night1 In recent years, laboratory investigations2,3,4, modelling studies5,6,7, measured Cl deficits in marine aerosols8 and species-nonspecific observations9,10,11 of gaseous inorganic chlorine compounds other than HCl have suggested that reactive halogen species may contribute significantly to—or even locally dominate—the oxidative capacity of the lower marine troposphere Here we report night-time observations of molecular chlorine concentrations at a North American coastal site during onshore wind flow conditions that cannot be explained using known chlorine chemistry The measured Cl2 mixing ratios range from <10 to 150 parts per 1012 (ppt), exceeding those predicted5 for marine air by more than an order of magnitude Using the observed chlorine concentrations and a simple photochemical box model, we estimate that a hitherto unrecognized chlorine source must exist that produces up to 330 ppt Cl2 per day The model also indicates that early-morning photolysis of molecular chlorine can yield sufficiently high concentrations of chlorine atoms to render the oxidation of common gaseous compounds by this species 100 times faster than the analogous oxidation reactions involving the OH radical, thus emphasizing the locally significant effect of chlorine atoms on the concentrations and lifetimes of atmospheric trace species in both the remote marine boundary layer and coastal urban areas

Inactivation of biofilm bacteria.

Abstract: The current project was developed to examine inactivation of biofilm bacteria and to characterize the interaction of biocides with pipe surfaces. Unattached bacteria were quite susceptible to the variety of disinfectants tested. Viable bacterial counts were reduced 99% by exposure to 0.08 mg of hypochlorous acid (pH 7.0) per liter (1 to 2 degrees C) for 1 min. For monochloramine, 94 mg/liter was required to kill 99% of the bacteria within 1 min. These results were consistent with those found by other investigators. Biofilm bacteria grown on the surfaces of granular activated carbon particles, metal coupons, or glass microscope slides were 150 to more than 3,000 times more resistant to hypochlorous acid (free chlorine, pH 7.0) than were unattached cells. In contrast, resistance of biofilm bacteria to monochloramine disinfection ranged from 2- to 100-fold more than that of unattached cells. The results suggested that, relative to inactivation of unattached bacteria, monochloramine was better able to penetrate and kill biofilm bacteria than free chlorine. For free chlorine, the data indicated that transport of the disinfectant into the biofilm was a major rate-limiting factor. Because of this phenomenon, increasing the level of free chlorine did not increase disinfection efficiency. Experiments where equal weights of disinfectants were used suggested that the greater penetrating power of monochloramine compensated for its limited disinfection activity. These studies showed that monochloramine was as effective as free chlorine for inactivation of biofilm bacteria. The research provides important insights into strategies for control of biofilm bacteria.

Some simple, highly reactive, inorganic chlorine derivatives in aqueous solution. Their formation using pulses of radiation and their role in the mechanism of the Fricke dosimeter

Abstract: In aqueous solution OH radicals react with chloride ions to form initially ClOH–, the rate constant being 4.3 ± 0.4 × 109 l. mol–1 s–1. The rate constant for the dissociation of ClOH– back to OH radicals and chloride ions is 6.1 ± 0.8 × 109 s–1. ClOH– is converted to chlorine atoms via the reaction, ClOH–+ H+→ Cl + H2O (k= 2.1 ± 0.7 × 1010 l. mol–1 s–1 at an ionic strength of unity), the rate constant for the reverse reaction being 1.3 × 103 l. mol–1 s–1(0.3–3.0 × 103 l. mol–1 s–1). Chlorine atoms combine with chloride ions to form Cl–2(k= 2.1 × 1010 l. mol–1 s–1), the rate constant for the dissociation of Cl–2 back to chlorine atoms and chloride ions being 1.1 ± 0.4 × 105 s–1.The absorption spectra of ClOH– and Cl–2 have been measured in the range 230–450 nm. Cl–2 absorption has a maximum at 340 nm where the extinction coefficient is 8.8 ± 0.5 × 103 l. mol–1 cm–1, whereas ClOH– has a maximum at 350 nm with an extinction coefficient of 3.7 ± 0.4 × 103 l. mol–1 cm–1.The reactions of chlorine atoms and Cl–2 with ferrous ions have also been investigated and the constants are 5.9 ± 0.6 × 109 and 1.4 ± 0.2 × 107 l. mol–1 s–1(ionic strength = 0.1 mol l.–1) respectively. The effect of chloride ions on the mechanism of the Fricke dosimeter is discussed.

A large atomic chlorine source inferred from mid-continental reactive nitrogen chemistry

Abstract: Chlorine atoms can profoundly affect the composition of the atmosphere. Notoriously, as chlorofluorocarbons, they were implicated in ozone depletion in the stratosphere. New observations suggest that chlorine may be a more potent force lower down in the atmosphere than was thought. The presence of gaseous chlorine atom precursors in the troposphere is generally considered a marine air phenomenon. But measurements made near Boulder, Colorado, reveal significant production of atmospheric nitryl chloride (ClNO2) in a continental setting, 1,400 km from the nearest coastline. This finding, incorporated into model studies, suggests that nitryl chloride production in the contiguous United States alone — probably arising from anthropogenic pollutants — is at a level similar to previous global estimates for marine regions. The presence of gaseous chlorine atom precursors within the troposphere was thought only to occur in marine areas but now nitryl chloride has been found at a distance of 1,400 km from the nearest coastline. A model study shows that the amount of nitryl chloride production in the continental USA alone is similar to previous global estimates for marine regions. A significant fraction of tropospheric chlorine atoms may arise directly from anthropogenic pollutants. Halogen atoms and oxides are highly reactive and can profoundly affect atmospheric composition. Chlorine atoms can decrease the lifetimes of gaseous elemental mercury1 and hydrocarbons such as the greenhouse gas methane2. Chlorine atoms also influence cycles that catalytically destroy or produce tropospheric ozone3, a greenhouse gas potentially toxic to plant and animal life. Conversion of inorganic chloride into gaseous chlorine atom precursors within the troposphere is generally considered a coastal or marine air phenomenon4. Here we report mid-continental observations of the chlorine atom precursor nitryl chloride at a distance of 1,400 km from the nearest coastline. We observe persistent and significant nitryl chloride production relative to the consumption of its nitrogen oxide precursors. Comparison of these findings to model predictions based on aerosol and precipitation composition data from long-term monitoring networks suggests nitryl chloride production in the contiguous USA alone is at a level similar to previous global estimates for coastal and marine regions5. We also suggest that a significant fraction of tropospheric chlorine atoms6 may arise directly from anthropogenic pollutants.

Arsenic — a Review. Part II: Oxidation of Arsenic and its Removal in Water Treatment

Abstract: In natural waters arsenic normally occurs in the oxidation states +III (arsenite) and +V (arsenate). The removal of As(III) is more difficult than the removal of As(V). Therefore, As(III) has to be oxidized to As(V) prior to its removal. The oxidation in the presence of air or pure oxygen is slow. The oxidation rate can be increased by ozone, chlorine, hypochlorite, chlorine dioxide, or H2O2. The oxidation of As(III) is also possible in the presence of manganese oxide coated sands or by advanced oxidation processes. Arsenic can be removed from waters by coprecipitation with Fe(OH)3, MnO2 or during water softening. Fixed-bed filters have successfully been applied for the removal of arsenic.The effectiveness of arsenic removal was tested in the presence of adsorbents such as FeOOH, activated alumina, ferruginous manganese ore, granular activated carbon, or natural zeolites. Other removal technologies are anion exchange, electrocoagulation, and membrane filtration by ultrafiltration, nanofiltration or reverse osmosis.