The Experts below are selected from a list of 3477 Experts worldwide ranked by ideXlab platform
L Sanche - One of the best experts on this subject based on the ideXlab platform.
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effects of cosmic rays on atmospheric chlorofluorocarbon dissociation and ozone depletion
Physical Review Letters, 2001Co-Authors: L SancheAbstract:Data from satellite, balloon, and ground-station measurements show that ozone loss is strongly correlated with cosmic-ray ionization-rate variations with altitude, latitude, and time. Moreover, our laboratory data indicate that the dissociation induced by cosmic rays for CF(2)Cl(2) and CFCl(3) on ice surfaces in the polar stratosphere at an altitude of approximately 15 km is quite efficient, with estimated rates of 4.3 x 10(-5) and 3.6 x 10(-4) s(-1), respectively. These findings suggest that dissociation of Chlorofluorocarbons by capture of electrons produced by cosmic rays and localized in polar stratospheric cloud ice may play a significant role in causing the ozone hole.
Matthias Nutzel - One of the best experts on this subject based on the ideXlab platform.
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possible implications of enhanced chlorofluorocarbon 11 concentrations on ozone
Atmospheric Chemistry and Physics, 2019Co-Authors: Martin Dameris, Patrick Jockel, Matthias NutzelAbstract:Abstract. This numerical model study is motivated by the observed global deviation from assumed emissions of chlorofluorocarbon-11 (CFC-11, CFCl3 ) in recent years. Montzka et al. (2018) discussed a strong deviation of the assumed emissions of CFC-11 over the past 15 years, which indicates a violation of the Montreal Protocol for the protection of the ozone layer. An investigation is performed which is based on chemistry–climate model (CCM) simulations that analyze the consequences of an enhanced CFC-11 surface mixing ratio. In comparison to a reference simulation (REF-C2), where a decrease of the CFC-11 surface mixing ratio of about 50 % is assumed from the early 2000s to the middle of the century (i.e., a mixing ratio in full compliance with the Montreal Protocol agreement), two sensitivity simulations are carried out. In the first simulation the CFC-11 surface mixing ratio is kept constant after the year 2002 until 2050 (SEN-C2-fCFC11_2050); this allows a qualitative estimate of possible consequences of a high-level stable CFC-11 surface mixing ratio on the ozone layer. In the second sensitivity simulation, which is branched off from the first sensitivity simulation, it is assumed that the Montreal Protocol is fully implemented again starting in the year 2020, which leads to a delayed decrease of CFC-11 in this simulation (SEN-C2-fCFC11_2020) compared with the reference simulation; this enables a rough and most likely upper-limit assessment of how much the unexpected CFC-11 emissions to date have already affected ozone. In all three simulations, the climate evolves under the same greenhouse gas scenario (i.e., RCP6.0) and all other ozone-depleting substances decline (according to this scenario). Differences between the reference (REF-C2) and the two sensitivity simulations (SEN-C2-fCFC11_2050 and SEN-C2-fCFC11_2020) are discussed. In the SEN-C2-fCFC11_2050 simulation, the total column ozone (TCO) in the 2040s (i.e., the years 2041–2050) is particularly affected in both polar regions in winter and spring. Maximum discrepancies in the TCO values are identified with reduced ozone values of up to around 30 Dobson units in the Southern Hemisphere (SH) polar region during SH spring (in the order of 15 %). An analysis of the respective partial column ozone (PCO) for the stratosphere indicates that the strongest ozone changes are calculated for the polar lower stratosphere, where they are mainly driven by the enhanced stratospheric chlorine content and associated heterogeneous chemical processes. Furthermore, it was found that the calculated ozone changes, especially in the upper stratosphere, are surprisingly small. For the first time in such a scenario, we perform a complete ozone budget analysis regarding the production and loss cycles. In the upper stratosphere, the budget analysis shows that the additional ozone depletion due to the catalysis by reactive chlorine is partly compensated for by other processes related to enhanced ozone production or reduced ozone loss, for instance from nitrous oxide ( NOx ). Based on the analysis of the SEN-C2-fCFC11_2020 simulation, it was found that no major ozone changes can be expected after the year 2050, and that these changes are related to the enhanced CFC-11 emissions in recent years.
Jacques Bougard - One of the best experts on this subject based on the ideXlab platform.
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Adsorption of dichlorodifluoromethane, chlorodifluoromethane, and chloropentafluoroethane on activated carbon
Journal of Chemical & Engineering Data, 1995Co-Authors: Karl Berlier, Marc Frère, Jacques BougardAbstract:The CFCs (Chlorofluorocarbons) are used as working refrigerant fluids. Recent concerns of the effects of CFCs on the ozone layer requires the development of efficient recovery methods. One technique is to adsorb the fluids onto a porous medium such as silica gel or activated carbon. Isotherms and enthalpies of adsorption curves of dichlorodifluoromethane (R12), chlorodifluoromethane (R22), and chloropentafluoroethane (R115) on three different activated carbons have been obtained at 303 K and at pressures to 602 kPa.
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adsorption of dichlorodifluoromethane chlorodifluoromethane chloropentafluoroethane 1 1 difluoroethane and 1 1 1 2 tetrafluoroethane on silica gel
Journal of Chemical & Engineering Data, 1994Co-Authors: Marc Frère, Karl Berlier, Jacques Bougard, Roger JadotAbstract:The CFC's (Chlorofluorocarbons) are used as working refrigerants fluids. The most commonly used are R12, R22, and R502 (48.8% R22 and 51.2% R115). Recent concerns of the effects of CFC's on the ozone layer require the development of efficient recovery methods. One technique is to adsorb the fluids onto a porous medium such as silica gel. Thermodynamic data on the adsorption of dichlorodifluoromethane (R12), chlorodifluoromethane (R22), chloropentafluoroethane (R115), 1,1-difluoroethane (R152a), and 1,1,1,2-tetrafluoroethane (R134a) on silica gel are required for the design of recovery units. The results are presented here.
John L Bullister - One of the best experts on this subject based on the ideXlab platform.
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chlorofluorocarbon 11 removal in anoxic marine waters
Geophysical Research Letters, 1995Co-Authors: John L Bullister, B H LeeAbstract:Measurements of the Chlorofluorocarbons CCl{sub 3}F (F-11) and CCl{sub 2}F{sub 2}(F-12) made in the subsurface anoxic zones of the Black Sea and Saanich Inlet, B.C., Canada show a pronounced depletion of dissolved F-11. These zones are strongly reducing and are characterized by the absence of dissolved nitrate (NO{sub 3}{sup {minus}}) and the presence of hydrogen sulfide (H{sub 2}S). Models incorporating the atmospheric input histories of these CFCs and the observed distributions are used to estimate residence times for water in these zones and first order in-situ removal rates for F-11. In contrast, measurements in the mid-depth low-oxygen zone of the eastern Pacific (where NO{sub 3}{sup {minus}} is present and H{sub 2}S is below detection limits) do not show evidence of similar rapid F-11 removal. 22 refs., 3 figs., 1 tab.
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a chlorofluorocarbon section in the eastern north atlantic
Deep Sea Research Part A. Oceanographic Research Papers, 1992Co-Authors: Scott C Doney, John L BullisterAbstract:Abstract We present the distributions of two Chlorofluorocarbons (CFCs) CFC-11 and CFC-12, measured as part of a hydrographic section between Iceland and the equator during July and August 1988. CFC-tagged water has filled the entire subpolar water column and subtropical thermocline in the eastern North Atlantic. Measurable CFC concentrations are observed at the ocean bottom as far south as 35°N, and the CFC penetration depth shoals to ≈750 m in the tropics. Specific features in the CFC distributions include a clear signal of Labrador Sea mid-depth ventilation, a CFC-enriched overflow water boundary current along the Iceland slope, and a mid-depth, equatorial plume of upper North Atlantic Water. The CFC data are used, in conjuction with the hydrographic data from the cruise, to illustrate the ventilation time-scales and pathways for the water masses in the eastern basin. A subsurface CFC maximum at about 100–200 m depth in the subtropics is shown to be a by-product of the heating and degassing of the seasonal thermocline and of the temperature sensitivity of CFC solubility. The CFC concentrations in the subpolar mode water are undersaturated by 15–18% relative to the atmosphere, reflecting the age of the mode waters and the very deep winter mixed layers in the eastern subpolar gyre. The CFC concentrations in the oxygen minimum off tropical Africa are much lower than the concentrations in the subtropical gyre, supporting previous work that suggests that isolation and enhanced productivity both contribute to the formation of the tropical oxygen minimum. In addition, the CFC inventories at the tropical stations have increased between 1982 and 1983 (TTO/TAS) and the summer of 1988 at a slower rate relative to the subtropical inventories over the same period. Thermocline oxygen utilization rates calculated from the CFC concentration data range from 5 to 10 μmol kg −1 y −1 and are in line with previous estimates for the eastern subtropical thermocline. The low CFC concentrations in Mediterranean Water, about one-quarter those in the Labrador Sea Water, are shown to result from entrainment near the Straits of Gibraltar of a large component of low CFC, lower Atlantic thermocline water. Based on the CFC and other transient tracer distributions, the deep eastern basin can be divided into two regions: the Iceland Basin and surrounding area influenced by Iceland-Scotland Overflow Water that is ventilated on a decadal time-scale, and the area south of ≈50°N that has little or no CFC and is ventilated from a southern source on a much longer time-scale. A northward flowing boundary current of low CFC, modified Eastern Basin Bottom Water is also found along the Rockall Plateau and in the Iceland Basin.
Marc Frère - One of the best experts on this subject based on the ideXlab platform.
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Adsorption of dichlorodifluoromethane, chlorodifluoromethane, and chloropentafluoroethane on activated carbon
Journal of Chemical & Engineering Data, 1995Co-Authors: Karl Berlier, Marc Frère, Jacques BougardAbstract:The CFCs (Chlorofluorocarbons) are used as working refrigerant fluids. Recent concerns of the effects of CFCs on the ozone layer requires the development of efficient recovery methods. One technique is to adsorb the fluids onto a porous medium such as silica gel or activated carbon. Isotherms and enthalpies of adsorption curves of dichlorodifluoromethane (R12), chlorodifluoromethane (R22), and chloropentafluoroethane (R115) on three different activated carbons have been obtained at 303 K and at pressures to 602 kPa.
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adsorption of dichlorodifluoromethane chlorodifluoromethane chloropentafluoroethane 1 1 difluoroethane and 1 1 1 2 tetrafluoroethane on silica gel
Journal of Chemical & Engineering Data, 1994Co-Authors: Marc Frère, Karl Berlier, Jacques Bougard, Roger JadotAbstract:The CFC's (Chlorofluorocarbons) are used as working refrigerants fluids. The most commonly used are R12, R22, and R502 (48.8% R22 and 51.2% R115). Recent concerns of the effects of CFC's on the ozone layer require the development of efficient recovery methods. One technique is to adsorb the fluids onto a porous medium such as silica gel. Thermodynamic data on the adsorption of dichlorodifluoromethane (R12), chlorodifluoromethane (R22), chloropentafluoroethane (R115), 1,1-difluoroethane (R152a), and 1,1,1,2-tetrafluoroethane (R134a) on silica gel are required for the design of recovery units. The results are presented here.
