Fire Suppression Substitutes and Alternatives to Halon for U.S. Navy Applications (1997) / Chapter Skim
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ATMOSPHERIC CHEMISTRY AND EVALUATION OF ENVIRONMENTAL EFFECTS OF FIRE SUPPRESSANTS
ATMOSPHERIC CHEMISTRY AND EVALUATION OF ENVIRONMENTAL EFFECTS OF FIRE SUPPRESSANTS
Pages 22-44
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Stratospheric ozone is important because it absorbs much of the intense ultraviolet (UV) radiation from the sun, dissociating into O2 and O
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It was not until the early 1980s that ground-based and satellite data were sufficient to determine a clear trend. Direct measurements now show that stratospheric ozone depletion has occurred during the past two decades.s In fact, the extent of ozone depletion is larger than predicted by the models based on gasphase chemistry.
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These reactions involving bromine are especially effective in the lower stratosphere, where much of He observed ozone depletion occurs. In addition to these catalytic cycles, Here are a very large number of cycles involving nitrogen oxides, hydrogenated species, and halogen species.
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, Radiative Forcing of Climate Change, Cambridge University Press, Cambridge, Great Britain (1996~. 4 World Meteorological Organization, Scientific Assessment of Ozone Depletion, (1994~; World Meteorological Organization, Global Ozone Research and Monitoring Project, Report No.
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ATMOSPHERIC LIFETIME, OZONE DEPLETION POTENTIAL, AND GLOBAL WARMING POTENTIAL AS INDICATORS OF ENVIRONMENTAL IMPACT Compounds being considered as replacements for halon include perfluorocarbons, hydrofluorocarbons, hydrochiorofluorocarbons, and several other compounds, such as CF31 and SF6. These compounds are listed in Table 3.1, along with their atmospheric lifetimes and calculated ozone depletion potentials.
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Mandronich, "Radiation Amplification Factors: Improved Formulation Accounts for Large Increases in Ultraviolet Radiation Associated with Antarctic Ozone Depletion," pp. 39-42 in Ultraviolet Radiation ir' Antarctica: Measurements and Biological Research, C.S.
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for Halons and for Potential Replacements ChemicalAtmospheric Lifetime Ozone Depletion Species Formula(years) Potential HALONS H-1211 CF2ClBr20 5 H-1301 CF3Br65 13 H-2402 CF2BrCF2Br20 7 HCFCs HCFC-22 CF2HC112.1 0.05 HCFC-123 CF3CHCl21.4 0.02 HCFC-124 CF3CHFC16.1 0.03 HFCs HFC-23 CHF3264 ~0 HFC-32 CH2F25.6 0 HFC- 125 CF3CF2H32.6 ~0 HFC-134a CH2FCF314.6 ~0 HFC-227ea CF3CHFCF336.5 0 HFC-236fa CF3CH2CF3209 0 PFCs FC-14 CF450000 0 FC- 116 C2F610000 0 FC-218 C3F~>2600 0 FC-31-10 C4Flo>2600 0 FC-51-14 C6F~43200 0 OTHER CFC-l l CFC1350 1 Carbon dioxode CO2 Sulfur SF63200 0 hexafluonde Trifluoroiodo- CF3I~ 0.005 ~ 0.008 methane NOTE: Most of the values for abrnospheric lifetime are based on recent international assessments and references therein (IPCC, 1996~.
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on globally integrated ozone distribution. Ozone Depletion Potential The concept of ozone depletion potential (ODP)
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, the perfluorocarbons (PFCs) , and sulfur hexafluoride are all near zero, reflecting the inability of their degradation products to participate in catalytic ozone destruction cycles.26 Although the HCFCs do contain chlorine and can affect ozone, the ODPs of those being considered as halon replacements (Table 3.1)
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For example, emissions of haloes result in stratospheric bromine that can destroy stratospheric ozone, which is also a greenhouse gas.3 ~ Such indirect effects need to be considered when candidate replacement compounds are evaluated for potential effects on climate.
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SOURCE: Adapted from IPCC, 1996, and from World Meteorological Organ~zation, Scientific Assessment of Ozorze Depletion, 1994. Relative Radiative Forcing per Molecule or Mass Relative radiative forcing represents a comparison of radiative forcing on a molecule-per-molecuTe or kilogram-per-kilogram basis for the different greenhouse gases.
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Navy account for an even smaller fraction of the radiative forcing effects on climate. Global Warming Potential Akin to the concept of ODE, the concept of global warming potential has been developed to provide a simple representation of the relative effects on climate resulting from a unit-mass emission of a greenhouse gas.
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The very Tong atmospheric lifetimes of these gases lead to extremely large GWPs. These large GWPs imply potentially large effects on climate over long time scales, with the actual effect on climatic radiative forcing dependent on the magnitude of emissions into the atmosphere.
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Summary The concepts of ozone depletion potential and global warming potential provide important guides to the potential of halon replacements to destroy stratospheric ozone and to affect radiative forcing on climate. In general, unless the amounts of replacement compounds produced and emitted into the atmosphere are much larger than the amounts of the compounds they replace, the compounds being considered as halon replacements are not expected to have any appreciable effect on stratospheric ozone.
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HE is an efficient and permanent sink for F atoms in the atmosphere, and as a result F atoms do not participate in catalytic chemical cycies.35 The value of the ozone depletion potential assigned to a compound is a combined measure of the amount of free radicals that it delivers to the stratosphere and the catalytic efficiency of the free radicals in ozone removal. ODPs measure the relative effects of different compounds on ozone on a per unit mass emitted basis, not on the basis of absolute concentrations of the halogen radicals delivered to the stratosphere.
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For all of the CFCs, HCFCs' and HFCs that have been examined, the lifetimes of the intermediate atmospheric degradation products are always much shorter than those of the parent compounds. As a result, the atmospheric concentrations of the intermediate products are always much smaller than those of the parent compounds.
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For CF3CHFO radicals there are two important pathways. The first is C-C bond scission and the second is reaction with Table 3.4 Atmospheric Degradation Products of Selected Fluorocarbons Fluorocarbon S~uctural Formula Intermediate Degradation Products Fmal Degradation Products HCFC-22 CHC1F2 CF2O HF, HC1, CO2 HFC-23 CF3H CF2O, CF3OH HF, CO2 IFC-13I1 CF3I CF2O, CF3OH HF, HI, CO2 HCFC-123 CF3CHCl2 CF3C(O)
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II, World Meteorological Organization, Global Ozone Research and Monitoring Project- Report No. 20, Geneva (1990~; and T.J.
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The aldehydes and acid halides are soluble in water and will then react further to form halogenated acids or hydrogen halides and carbon dioxide. The probable degradation products for the haloethanes are summarized in Table 3.4.
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These questions have been answered by recent experimental studies that have shown that the lifetimes of the intermediate products are much shorter than the transport time to the stratosphere, and hence the intermediate oxidation products do not act as carriers of chlorine/bromine atoms to the stratosphere. Accumulation of Degradation Products in the Biosphere Given the expected emission rates and the kinetic data available, it is unlikely that the concentrations of the intermediate products in the global atmosphere will approach the parts per trillion level.
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7. World Meteorological Organization, Scientific Assessment of Ozone Depletion (1994~; World Meteorological Organization, Global Ozone Research and Monitoring Project, Report No.
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23. World Meteorological Organization, Scientific Assessment of Ozone Depletion, 1991, World Meteorological Organization, Global Ozone Research and Monitoring Project Report, No.
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57. Review in Chapter 12 of World Meteorological Organization, Scientific Assessment of Ozone Depletion' (1994~.
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