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Historic emissions of fluorotrichloromethane (CFC-11) based on a market survey
Atmospheric Environment 35 (2001) 4387–4397
Historic emissions of fluorotrichloromethane (CFC-11) based on a market survey A. McCullocha,*, P. Ashfordb, P.M. Midgleyc b
a School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK Caleb Management Services, Grovelands House, Woodlands Lane, Bristol BS32 4JT, UK c M&D Consulting, Ludwigstrae 49, D-70771 Leinfelden Musberg, Germany
Received 13 December 2000; received in revised form 10 April 2001; accepted 27 April 2001
Abstract Releases of CFCs occur promptly from applications such as aerosol sprays, or over a period of several years from refrigeration and air conditioning or more slowly still from use as blowing agents for closed cell plastic foams. As a consequence of the Montreal Protocol, the emissions have fallen and their pattern is continuing to change. To help quantify these changes the emissions from closed cell foam blowing have been re-examined in a comprehensive market survey, developing a lifecycle assessment for each foam type, production method and foaming agent. The original model for the time series of emissions from foam applications was shown to remain a robust representation in general terms. There is an ‘‘immediate’’ loss when the foam is manufactured, a slow emission from the foam itself during use and a loss on disposal of the artefact made with the foam. The original model used an initial loss rate of 10% and a subsequent loss of 4.5% yr1 over 20 yr. The new survey showed a wide range of initial and service loss rates. Immediate release ranges from 95% down to 4%; similarly, the rate of loss during service varies from 0.5% to 5% yr1 and the service lifetimes of the artefacts made with the foams varies from 12 to 50 yr. The apparent emission function, in terms of the mean value of the annual fractional release from the bank of CFC-11 residing in foams, was calculated from the survey to be 0.04370.008 over 28 yr. There is a small and non-significant fall in this function with time; so that over the last ten years of the data record the more appropriate value is 0.036670.0008. However, up to the early 1990s, it is the original emission function that is consistent with the observed atmospheric concentrations. Thenceforth this function seriously overpredicts the concentrations but, if the new emissions function for foams is used from 1993 onwards in conjunction with the original emission functions for all other uses, the fit becomes better. This suggests that the emission functions for prompt and short term releases remain valid and should be coupled with the new function to calculate emissions of CFC-11 or other fluorocarbon foam blowing agents from the early 1990s onwards. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Atmospheric concentration; Atmospheric lifetime; Foam blowing agent; Ozone depletion; Refrigerant
1. Introduction The Montreal Protocol has brought about an extensive reduction in the quantities of CFCs produced *Corresponding author. Present address: Marbury Technical Consulting, Barrymore, Marbury Road, Comberbach, Northwich CW9 6AU, UK. E-mail address: [email protected] (A. McCulloch).
and this is beginning to be reflected in falling atmospheric concentrations of materials such as CFC-11 (fluorotrichloromethane, CFCl3). The actual concentrations are related to the quantities emitted and the rate at which the material is removed from the atmosphere (its atmospheric lifetime). It is, therefore, possible to derive the atmospheric lifetime of a compound using data for the quantities emitted and measured atmospheric concentrations. This is one function of the advanced global atmospheric gases experiment (Prinn et al., 2000) which
1352-2310/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 0 1 ) 0 0 2 4 9 - 7
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uses emissions data for CFCs provided by the fluorocarbon industry (McCarthy et al., 1977; Gamlen et al., 1986; AFEAS, 2000). However, while historic productions are known accurately, the emissions calculated from them currently rely on functions developed some time ago and are much less certain. In many end uses, simple emission functions developed from information provided by chemical manufacturers are still valid and have been verified by independent market surveys. Thus emissions of aerosol propellants, open cell foam blowing agents and solvents are prompt and so can be assigned accurately in time. At least half of the quantity used is released in the year of manufacture and the remainder within the following year. The short delay allows for stockholding of materials in transit, at the industries using them and by the final customer. Refrigerants are released over the service life of the equipment: on average, 3–5 yr for the major uses in large industrial installations and automotive air conditioning, a characteristic time confirmed by a number of studies (Gamlen et al., 1986; March, 1992; Baker, 1999). However, emissions from closed cell foams present a more complex case with different matricesFpolyurethane, polystyrene and polyalkenes, for exampleFand different surface finishes with different gas permeabilities; all of which influence release patterns. The emissions functions for foam blowing originally developed by McCarthy et al. (1977), although relatively crude, allowed for an initial loss of blowing agent and thence loss at a constant rate throughout the service life until all of the agent had been released. They were applied to all sales of a particular CFC into closed cell foam blowing and have survived several re-examinations by the chemical manufacturers. However, since emissions have begun to fall as a consequence of the Montreal Protocol, the calculated concentrations no longer match the observations. Accordingly, the current practices and consequent releases from closed cell foam blowing have been re-examined in a comprehensive market survey (Ashford, 1999) and the results have been tested against observations of atmospheric concentrations. The main principle of the test is that the shape of the concentration trend generated from emissions data is relatively insensitive to assumptions about atmospheric lifetime or the absolute level of production and so may be used to assess the reliability of emission functions that have been developed independently. This paper describes the development of a global database for production and sales of CFC-11 and the tests applied to the emission functions of McCarthy et al. (1977) and Ashford (1999).
2. A global database of CFC-11 production 2.1. Calculation of the annual production quantities of all CFCs The alternative fluorocarbons environmental acceptability study (AFEAS), following on from studies conducted by the chemical manufacturers’ association (CMA), records audited production of CFCs and HCFCs in all of the developed and much of the less developed world (Argentina, Australia, Brazil, Canada, France, Germany, Greece, Italy, Japan, Mexico, Netherlands, South Africa, Spain, UK, USA and Venezuela) (AFEAS, 2000). However, similar data for China, Czech Republic, India, Korea (both North and South), Taiwan, Romania and Russia are not reported in this way. There are three other sources of time-series data for the additional production: McCarthy et al. (1977), Gamlen et al. (1986) and UNEP (1999), and a selfconsistent database needs to be constructed from the four sets of numbers. Production prior to 1986: For these early years, Gamlen and colleagues show reported sales of CFCs 11 and 12 together with estimates of additional sales, from countries not reporting to the industry survey (socalled ‘‘non-reporting countries’’). For the purposes of this calculation, sales can be taken to be equal to production. However, in the period from 1968 to 1975, when this estimate of additional sales overlaps with the estimate of additional production of CFCs 11 and 12 by McCarthy et al. (1977), the data do not agree; neither the absolute values nor the relative productions, one to the other, match. The remainder of the data in Gamlen et al. are identical to those in the latest AFEAS compendium and, to promote consistency, the values in McCarthy et al. (1977) were not used. The Gamlen data cover the period from 1968 (when production in non-reporting countries was essentially zero) to 1982 and were extended to commencement of the UNEP data in 1986 by linear interpolation. Production from 1986 to 1998: Annual CFC production from 1986 onwards, for each country individually, is recorded in UNEP (1999). These data are expressed as ODP tonnes and do not discriminate individual CFCs. However, it is possible to verify the AFEAS data (reported by manufacturers and audited) against the aggregate of data reported to UNEP by the authorities in the countries of the AFEAS list (shown above). On a common basis, the two sets of data agree year-by-year to within 1% over the period 1986–95. Given this consistency, the level of confidence in the remainder of the UNEP data should be similar. The ‘‘additional’’ production for the period 1986–97 that was not reported to AFEAS was taken directly from UNEP (1999) and is shown in Fig. 1. The 1998 data were obtained as a personal communication from Adila, UNEP, Kenya, 2001.
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The CFC-12 fraction of this residue follows a trend opposite to that of CFC-113, with a reduction towards 1990 at 0.0098 yr1 (R2 ¼ 0:93) and a subsequent increase at 0.04 yr1 (R2 ¼ 0:89). Applied to the additional production, this gives an estimate of the CFC-12 component and, by difference, the CFC-11. From the AFEAS database itself, the variance between the production of CFC-11 calculated in this way and the recorded actual production is 1.5%; this was used subsequently as a measure of uncertainty. From 1982 to 1986, the data were linearly interpolated between the estimate of Gamlen et al. (1986) and the results of the calculation described. The reported, audited CFC-11 production and estimate of additional production from 1950 to 1999 are shown in Table 1.
Fig. 1. Additional production of CFCs not included in the AFEAS database. The dashed line indicates the long term trend.
The composite data set for all CFCs was constructed from the AFEAS data, augmented with the additional production from Gamlen et al. (1986) and UNEP (1999).
2.2. Calculation of the quantity of CFC-11 produced Up to 1982, the values estimated for ‘‘non-reported’’ production of CFC-11 in Gamlen et al. (1986) were used. From 1986 onwards, the parties to the Montreal Protocol report this additional production to the United Nations Environment Programme, allowing a potentially more robust estimate of recent production. Unlike the manufacturers’ database, which discriminates individual CFCs, the UNEP data describe production of all CFCs together, expressed as ODP tonnes. Essentially the compilation comprises dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113) and CFC-11. It is assumed that the global proportions of these are the same as those recorded by AFEAS. This is consistent with the production reported by India (for 1999 only) in UNEP (2000) and the consumption reported for China (for 1997 only) in Yu Bingfeng et al. (2000). In the AFEAS database, the CFC-113 fraction follows two distinct trends: an increase to 1990 at 0.0136 yr1 (R2 ¼ 0:96) and a decrease thereafter at 0.0295 yr1 (R2 ¼ 0:89). The same distribution was applied to the additional production reported in UNEP (1999). After correcting the difference in ODP (0.8 for CFC-113 and unity for the others), the residue to be divided between CFCs 11 and 12 was calculated.
2.3. Calculation of quantities used for foam and for other categories Historically, CFC-11 was used principally in aerosol propellant mixtures, a totally emissive end use with a prompt release pattern. The next most significant use was to blow closed cell plastic foams, primarily destined for insulation applications where the service life of the product is measured in decades and the leakage rate during service is relatively small. In the AFEAS data, use in closed cell foam blowing is recorded from 1950 onwards; up to 1976 to the nearest 105 kg yr1 and thenceforward to the nearest 103 kg yr1. From these, the fractional use of CFC-11 in all forms of closed cell foam blowing can be calculated for the production reported to AFEAS. This fraction varies significantly from one year to the next, with an arithmetic mean of 0.35 and a distribution skewed towards values below the mean. There is also a wide spread in the absolute quantities from which the fractions are derived; from 4000 to 170,000 tonne yr1, with many of the larger fractional uses coinciding with large absolute quantities. The sales weighted average fraction for CFC-11 use in foams is 0.41, with a standard deviation of 0.41. There is no information on end use in the UNEP data and so the usage of CFC-11 in closed cell foam in the additional production was assumed to be the same as that in the AFEAS-reported production. This could be based on individual annual values or on a mean. The annual values exhibit wide swings, especially in recent years as the exigencies of the Montreal Protocol have become apparent and there is no reason to suppose that the large interannual variations in reported use outside of India, China and Russia should also be shown by their additional use. For the total CFC-11 use in closed cell foam, the difference between calculations using the sales-weighted average fraction (0.41) from the AFEASreported data and the individual annual values is 0.3% (RMS average). The sales weighted average was used to
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Table 1 Global production of CFC-11 and sales into closed cell foam
Year
1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Production (sales) reported to CMA or AFEAS
Additional production (sales)
CFC-11 (all uses) 103 kg
CC foam component 103 kg
CFC-11 (all uses) 103 kg
6623 9072 13562 17282 20911 26263 32477 33929 29529 35562 49714 60464 78109 93304 111085 122833 141022 159756 183116 217271 238136 263175 306856 349085 369724 314068 339832 320464 308852 289483 289619 286943 271443 291731 312355 326814 350148 382050 375986 302489 232916 213486 186434 147131 60232 32683 22123 18577 14600 12871
93 127 190 242 293 368 455 590 635 953 2087 2767 5670 8255 11158 13426 16828 19731 25401 31661 34156 42547 51710 62051 61916 55474 52073 65227 66089 80105 84051 97704 94937 97985 110638 117343 129618 160085 165982 164219 144438 148034 137941 106792 35109 14259 4186 6818 6777 7824
0 1000 2000 3000 4000 4900 7300 9900 12200 12500 14100 17500 20400 23100 38612 40437 42274 44111 44907 46846 48757 50640 50542 45788 37409 33238 41764 40831 31363 33113 31708 31487
Total quantity of CFC-11 used in CC foam
CC foam component 103 kg
103 kg
0 410 820 1230 1640 2009 2992 4058 5001 5124 5780 7173 8362 9469 15827 16575 17328 18081 18408 19202 19986 20757 20717 18768 15334 13624 17119 16737 12857 13573 12997 12906
93 127 190 242 293 368 455 590 635 953 2087 2767 5670 8255 11158 13426 16828 19731 25401 32071 34975 43777 53349 64060 64908 59532 57074 70351 71869 87278 92413 107173 110764 114560 127966 135424 148026 179287 185968 184976 165155 166802 153275 120416 52228 30996 17043 20391 19774 20730
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calculate the values reported in Table 1 and the difference was treated as a variance.
3. Emissions from foams 3.1. Physical factors affecting emissions functions CFC-11 was used to blow a number of plastic matrices but most of the closed cell foams (i.e. those that retain the blowing agent within the cells) were blown in polyurethane. These foams are rigid, unlike open cell foams, such as those used in furniture. The low thermal conductivity of CFC-11, conferred in part by its high molecular weight, meant that its foams were good thermal insulators. They were produced in a variety of forms: for domestic refrigerators, for example, the foam was blown in situ in the space between the outer shell (generally steel) and the food storage cabinet (generally plastic) and advantage was taken of the rigidity conferred by the foam itself in the structural integrity of the units. Foam in this sort of application was effectively contained within gas-impervious facings. At the other extreme, slabs used for building insulation were generally cut from a larger block of foam. In this form all surfaces of the foam were exposed to the atmosphere. Blowing agent is released into the atmosphere at three stages in the life of the foamFduring manufacture of the foam, during disposal at the end of its service life and during use, when the loss is generally small and slow. Typically, losses during manufacture occur from evaporation of the blowing agent before it becomes incorporated into the foam or from the scrap that is trimmed from foams that are blown as slabs. In many cases the plastic in the scrap foam may be recovered but the blowing agent is lost. Losses during use are thought to arise from slow migration of the blowing agent by dissolution in the matrix and re-evaporation to atmosphere (Norton, 1967). Potentially, material that is still in the foam at the end of its life may be recovered but this was seldom practiced for articles made with CFC blown foam (Quinn, 1978). 3.2. Original emission function (CMA and AFEAS) For the original emission function and as a result of examining the way that CFC foams were blown in the early 1970s, the CFC manufacturers decided that initial losses during foam manufacture were best represented by a single loss of 10%. The average service life of the foam, both as a board and as part of an article was estimated to be 20 yr and the remainder of the blowing agent was assumed to leak from the foam at a constant rate of 4.5% of the original quantity per year (McCarthy et al., 1977). This accounted for both the losses in service
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and on disposal. Clearly it is an oversimplification; foam contained between impervious facings is unlikely to have the same loss rate as board open to the atmosphere and the range of service lifetimes is much broader than that indicated by a single value of 20 yr. Nevertheless, the algorithm survived re-examination in the 1980s (Gamlen et al., 1986) and early 1990s (Fisher and Midgley, 1994). One reason for the longevity of this emission function is that it matches well with the way that manufacturers collect data (AFEAS, 2000). Audited sales are subdivided for each compound into end uses and there is a single category for all closed cell foam applications. Whatever emissions functions are adopted in the future, the historic data cannot now be reconstructed into more specific categories. It is unlikely that the fluorocarbon manufacturers could supply audited information for use in specific types of foam, even from now on. Such information may reside in the records of foam manufacturers but the number of manufacturers is too large to expect to obtain complete audited data year by year. However, a single comprehensive survey of the foam manufacturers should give a better view of current practices and the expectations for future emissions than the rather elderly information now in use. 3.3. New functions for foam manufacturing sectors During 1997 and 1998, a comprehensive global survey of foam manufacturing was carried out by Caleb Management Services (Ashford, 1999). This centred around interviews with key foam producers (35 interviews were conducted), coupled with data from technical literature and trade associations. The manufacturing sectors covered were: Polyurethane (PU) also known as polyisocyanurate (PIRA) integral skin foam, PU rigid insulation foams, used in or manufactured as: continuous and discontinuous panels; appliances and other systems blown in situ; continuous and discontinuous block; spray; continuous flexibly faced laminate. Extruded polystyrene foams Polyethylene foams, as: board; pipe. Phenolic foams, as: continuous flexibly faced laminate; discontinuous block. Each of these potentially has its own emission pattern and may involve the use of one or more CFC, HCFC or HFC. The compounds that were considered comprised
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CFCs 11 and 12, HCFCs 22, 141b and 142b and HFC134a; only CFC-11 is discussed in detail here. From the results of the interviews within the relevant industry sectors, a lifecycle assessment for current practice for each foam type, production method and foaming agent was developed. These were refined by cycling through a peer review process with the original interviewees and the UNEP technical options committee for foams. The general model for the time series of emissions from the foam applications was shown to remain a robust representation. There is an ‘‘immediate’’ loss when the foam is manufactured, a slow emission from the foam itself during use and a loss on disposal of the artefact made with the foam. The survey showed a wide range of initial and service loss rates. The immediate release ranges from 95% down to 4%; similarly, the rate of loss during service varies from 0.5% to 5% yr1 and the service lifetimes of the artefacts made with the foams varies from 12 to 50 yr. Surprisingly in view of the physical process by which the blowing agent dissolves out of the foam, losses are relatively insensitive to the nature of the blowing agent; the properties of the plastic matrix and the mechanics of the foam forming process are much more important. The complete set of loss parameters, together with their 1s uncertainties, is shown in Table 2.
construction rubble is landfilled. Only if the plastic foam is thermally oxidised in a properly operated incinerator will the blowing agent be destroyed; casual uncontained burning is likely to disrupt the plastic matrix allowing the blowing agent to escape without being properly oxidised. Historically, very little of the CFC-11 blown foam was incinerated (Quinn, 1978) and so total and immediate loss on disposal has been assumed for all of the applications at the end of their service life. 3.5. Quantities in each end use and total emissions from foams The market survey (Ashford, 1999) provided an independent estimate of the quantities of CFC-11 used in closed cell foam that agreed with the AFEAS data to within 7%. The data also quantified the annual use of CFC-11 in each type of foam, as shown in Table 3, and were used to distribute the total annual CFC-11 use (shown in Table 1) between foam applications. Then the annual global totals of emissions of CFC-11 from closed cell foams were calculated using the emissions functions for individual foam applications shown in Table 2. This estimate implies that the emissions functions are globally applicable; that the pattern of emissions in time depends only on the foam application and is independent of the geographical region where the CFC-11 is used.
3.4. Loss on disposal 4. Emissions from all categories When the appliance or building using the insulating foam becomes surplus to requirements the foam represents only a small part of the total disposal problem. Most commonly, the foamed plastic is not separated from the rest of the scrap and the residual blowing agent is released when appliances are crushed or
The AFEAS compendium (AFEAS, 2000) contains separate estimates for the emissions from aerosol propulsion (50% released immediately and 50% in the following year), open cell foam (83% released immediately and 17% in the following year) and refrigeration,
Table 2 Contemporary emission patterns from plastic foams
Application a
PU integral skin PU continuous panel PU discontinuous panel PU appliance PU blown in situ PU continuous block PU discontinuous block PU continuous laminate PU spray Phenolic laminate Phenolic block a
PU signifies polyurethane.
Fraction released
Fraction released
Service life of equipment
Initially
Uncertainty
Annually
Uncertainty
Years
Uncertainty
0.95 0.075 0.0125 0.04 0.06 0.35 0.4 0.1 0.25 0.1 0.4
0.0125 0.0125 0.0125 0.005 0.005 0.005 0.005 0.025 0.025 0.025 0.05
0.025 0.005 0.005 0.0025 0.0025 0.0075 0.0075 0.015 0.015 0.015 0.0075
0.00675 0.00125 0.00125 0.001 0.001 0.0015 0.0015 0.0025 0.0025 0.0025 0.0015
25 25 15 15 15 15 60 50 60 15
2.5 2.5 2.5 2.5 2.5 2.5 10 10 10 2.5
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A. McCulloch et al. / Atmospheric Environment 35 (2001) 4387–4397 Table 3 Distribution of CFC-11 consumption in closed cell foam blowing between foam types, expressed as percent of the total Year Polyurethane
1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Phenolic
Integral Continuous Discontinuous Appliance Blown Continuous Discontinuous Laminate Spray skin panel panel in situ block block
Laminate Block
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 2 4 6 8 10 11 12 12 12 12 12 12 12 12 12 11 9 6 5 3 2 1 1 1 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 3 5 6 7 7 7 8 7 7 7 6 6 6 7 8 9 9 9 9 9 10 8 9 10 10
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 10 12 17 17 16 15 14 13 12 11 10 9 8 8 8 8 8 8 8 7 7 6 7 7 8 8 8 8 8 9 13 18 24 31
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 6 11 17 20 20 20 20 19 19 19 19 19 19 20 21 23 24 25 26 26 27 28 29 30 32 37 44 40 35 30
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 12 13 16 16 14 12 11 10 9 8 8 7 7 6 6 6 6 6 5 5 5 5 5 6 7 8 10 12 13 13 10 8 7 5
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 3 3 2 3 3 4 3 3 3 3 3 3 3 3 3 2 2 2 3 3 3 3 2 2 2 1 0 0 0
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 82 62 42 27 19 11 8 7 6 5 5 4 4 4 4 4 4 3 3 3 3 3 2 2 3 3 3 3 2 2 2 1 1 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 16 33 39 46 47 47 43 41 39 37 35 33 33 33 33 33 32 33 33 33 34 33 32 30 27 26 25 23 20 12 6 4 2 2
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 2 3 5 6 7 8 8 8 8 8 8 8 8 7 7 7 7 8 9 10 10 10 12 14 16 19 21 22
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0
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which for CFC-11 is classed as all being non-hermetic. The rate of release from non-hermetic refrigeration is distributed approximately normally about a mean of 4.5 yr. Thus emissions in the first year are small, grow to a maximum at 4.5 yr and subsequently all of the refrigerant is estimated to be released within 10 yr of being charged into the equipment. This pattern reflects the fact that releases during the operation of nonhermetic refrigeration systems are significant and inherent in the design of the equipment. These releases were augmented by emissions calculated from the additional production not included in the AFEAS data but comprising part of the UNEP database, which was treated as being used in refrigeration and closed cell foam only. The total calculated annual emissions and the contributions from refrigeration, other uses (aerosol and open cell foams), additional refrigeration and closed cell foam blowing are shown in Table 4. Characteristically, the emission of blowing agent from closed cell foams is dominated by releases, both during operation and at end-of-life, from the insulation now installed. In the case of CFC-11 this is accentuated by the rapid decline in sales for closed cell foam in recent years, shown in Table 1. With little or no further addition to the bank and no change in the social factors acting on emissive practices, for example, legislation on recovery or destruction of blowing agent at end-of-life, the rate of emission should tend towards a constant fraction of the bank. Fig. 2 shows that the annual fraction of the bank in foams that is calculated to be emitted tended towards a constant value for the mature market. Over 28 yr, the rate of emission calculated in this way is approximately represented by the relationship in Eq. (1)
of 2 yr (Gamlen et al., 1986). Monte Carlo combination of the uncertainties for each of these end uses, assuming normal distributions and typical standard deviations, gave values for the coefficients of variation of each end use in each year. These were combined, weighted by the annual mean emissions, with the coefficients of variation in short term emissions (fugitive, aerosol and open cell foams) and additional production. For the short term emissions the uncertainty is 0.5%, which is essentially the uncertainty in the absolute quantity falling into this category, the rate of release having been shown to have no significant effect when emissions are accounted annually (Gamlen et al., 1986; Fisher and Midgley, 1994). The additional production is subject to several sources of uncertainty: a variance of 0.5% arises from uncertainty in the product mix, as described in Section 2.2 above, a variance of 0.3% arises from uncertainty in the calculation of the fraction used in closed cell foam and a further 1% accounts for the difference between the UNEP and AFEAS databases. Based on the contemporary emission functions, the emissions and combined annual uncertainties at 2s are shown in Table 4.
R ¼ 0 0613 0 000534T;
Cy ¼ ST þ ðCy1 STÞexpð1=TÞ;
ð1Þ
where R is the annual fraction of the bank released and T is the year number, with zero in 1950 in this case. The coefficient of variance (R2 ) for this line is only 35%, suggesting that the slope cannot be considered significant and the mean value over this period (0.04370.008) is a valid description of the calculated release rate. Nevertheless, the better description of the more recent emission function, over the last 10 years of the data record, is somewhat lower at 0.036670.0008.
5. Uncertainty Uncertainty in the calculated emissions from foams arises from uncertainties in the quantity lost initially, in the annual losses and in the lifetime over which the losses occur, as shown in Table 2. Losses from refrigeration are calculated as described in Section 4 above using a normal distribution about a mean lifetime of the equipment; in this case, 4.5 yr, with an uncertainty
6. Calculated atmospheric concentrations Fig. 3 shows the average tropospheric concentrations of CFC-11 calculated from the new emissions over the whole database for atmospheric lifetimes of 52, 40 and 76 yr; representing, respectively, the mean and the extremes of the optimal estimation of lifetime as described in Prinn et al. (2000). The concentrations were estimated at yearly intervals using the formula in Eq. (2) (SORG, 1990). ð2Þ
where Cy and Cy1 are the average atmospheric concentrations in a year and in the previous year, S is the emission during the year and T is the average atmospheric lifetime in years. According to the Scientific Assessment of Ozone Depletion, 1998 (Prinn and Zander, 1999; Prinn et al., 2000), the atmospheric concentration of CFC-11 levelled off in the mid-1990s and has begun to decrease. The shapes of the curves in Fig. 3 agree in a general sense with that observation, but the rate of decline in measured tropospheric concentrations is greater than that calculated (even at the shortest lifetime) and the measurements up to 1990 are matched only by calculations using the longest lifetime. The shape of the observed concentration curve cannot be matched by changing only the lifetime. The recommended atmospheric lifetime for CFC-11, based on calculations using a number of modelling techniques that go beyond the mass balance described in Prinn et al. (2000), is 4577 yr (Prinn and Zander, 1999).
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A. McCulloch et al. / Atmospheric Environment 35 (2001) 4387–4397 Table 4 Calculated global emissions of CFC-11 based on a combination of contemporary and historic emission functions Global emissions of CFC-11 Year
1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Sectorial emission (from AFEAS data)
Additional emission (this work)
Refrigeration (106 kg)
Other (106 kg)
Refrigeration (106 kg)
CC foam (106 kg)
0.22 0.24 0.31 0.43 0.59 0.79 1.02 1.32 1.69 2.11 2.64 3.24 3.86 4.53 5.18 5.81 6.49 7.17 7.89 8.72 9.61 10.6 11.7 13.1 14.5 15.8 17.6 19.0 20.6 22.5 24.3 25.9 26.8 27.4 27.1 26.7 26.1 25.9 26.2 26.5 26.7 26.5 25.5 23.7 21.4 19.0 16.5 14.0 11.6 9.2
5.25 7.37 10.6 14.5 17.9 22.1 27.6 30.7 28.3 28.5 37.4 48.2 60.3 73.6 87.1 99.0 110 125 141 164 186 202 227 258 283 269 271 253 228 201 183 172 159 167 180 185 194 200 197 141 89.2 56.3 37.6 27.2 17.8 10.4 10.6 7.6 4.6 4.0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.04 0.14 0.32 0.56 1.02 1.57 2.25 3.08 3.99 5.01 6.12 7.25 8.45 10.3 12.4 15.0 17.9 20.6 22.9 24.7 26.1 27.1 27.8 27.9 27.4 26.6 25.3 23.9 22.9 22.0 21.1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.08 0.15 0.22 0.29 0.36 0.60 0.96 1.37 1.48 1.89 2.37 2.93 3.26 5.65 5.84 6.03 6.39 6.43 6.72 7.31 7.90 8.12 7.00 5.81 6.36 16.3 28.1 39.0 37.7 38.4 38.1
AFEAS CC foam emission 6 (10 kg)
Using AFEAS emission function (106 kg)
Using new emission function throughout (106 kg)
Recommended value (106 kg)
0.01 0.02 0.04 0.05 0.07 0.10 0.13 0.17 0.20 0.28 0.49 0.68 1.24 1.87 2.68 3.50 4.62 5.79 7.54 9.58 11.4 14.2 17.4 21.3 24.0 25.8 27.7 32.1 35.0 40.1 44.0 49.9 53.3 57.9 63.5 69.0 75.1 84.7 91.4 97.5 100 106 108 107 98.3 94.4 91.1 89.0 86.0 83.1
5.49 7.63 11.0 15.0 18.6 23.0 28.7 32.2 30.2 30.9 40.5 52.1 65.4 80.0 95.0 108 121 138 157 182 207 227 257 294 324 314 321 309 291 272 261 260 255 271 292 305 322 340 347 299 251 223 205 192 181 178 182 172 164 156
5.44 7.74 11.0 15.0 18.6 23.2 28.7 32.2 30.3 31.0 41.0 52.6 66.5 81.5 97.0 110 122 137 154 178 202 221 248 284 312 301 308 296 277 258 246 243 236 248 267 278 292 312 316 264 208 173 149 134 112 100 95.6 88.3 81.3 76.4
5.5 7.6 11.0 15.0 18.6 23.0 28.7 32.2 30.2 30.9 40.5 52.1 65.4 80.0 95.0 108.3 121.3 137.6 156.8 182.0 206.9 227.5 256.6 293.8 323.6 314.1 321.1 309.4 290.5 272.1 261.0 259.9 255.4 271.0 292.1 305.1 322.1 340.3 346.5 299.2 251.3 223.2 205.0 191.9 111.9 100.3 95.6 88.3 81.3 76.4
Using the mean mass balance lifetime of 52 yr and the new emissions functions, concentrations calculated for the whole of the time that CFC-11 has been emitted into the atmosphere seriously understate
Uncertainties (106 kg) +2s
2s
6.0 8.2 11.5 15.5 19.2 23.8 29.6 33.2 31.5 32.4 42.3 54.2 67.6 82.5 97.6 111.0 124.2 140.7 160.0 185.6 210.9 231.9 261.7 299.8 330.2 320.1 328.7 317.2 299.0 281.3 269.9 268.0 263.8 279.3 300.8 313.7 331.3 351.5 360.8 313.3 263.8 235.9 219.6 208.9 125.7 116.4 113.3 106.6 100.4 98.4
5.0 7.1 10.5 14.4 17.9 22.3 27.9 31.1 28.8 29.4 38.8 50.1 63.1 77.6 92.4 105.6 118.3 134.5 153.6 178.4 202.9 223.1 251.5 287.8 317.0 308.2 313.6 301.6 282.0 263.0 252.2 251.9 247.1 262.8 283.4 296.5 312.9 329.0 332.2 285.1 238.9 210.5 190.5 174.9 98.1 84.3 78.0 69.9 62.3 54.5
the observed values. A difference of only 2 pmol mol1 in 1980, rises through 10 in 1985 to reach 20 pmol mol1 in 1990. These differences are statistically significant at 2s:
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Fig. 2. Calculated fraction of the bank of CFC-11 retained in foams that is released annually. The trend from 1970 onwards quantified in Eq. (1) is shown as the dotted line.
Fig. 4. Atmospheric concentrations of CFC-11 calculated using the AFEAS emission functions throughout (dashed line) and the AFEAS functions for foam emissions to 1993 and the new function thereafter (solid line). The dotted lines show uncertainties at 2s and measured concentrations are shown as filled squares.
the new emissions function for foams is used from 1993 onwards in conjunction with the original emission functions for all other uses, the fit becomes better.
7. Conclusions
Fig. 3. Atmospheric concentrations of CFC-11 calculated with the new emission functions using atmospheric lifetimes of 40, 52 and 76 yr. The dotted lines show uncertainties at 2s and the filled squares are the observed concentrations.
Not surprisingly, the concentrations calculated from the AFEAS emission function using the mean mass balance lifetime are in much better agreement with measurements up to 1990. Fig. 4 shows the global average of the measured concentrations as reported by Prinn et al. (2000) and the concentrations calculated from the original AFEAS data (AFEAS, 2000) (with allowance for emissions from additional production) using the original emission functions (Gamlen et al., 1986) and the mean lifetime of 52 yr. Up to the early 1990s, the fit is good but thenceforth these emissions seriously overpredict the atmospheric concentration. If
With the change in use pattern of CFC-11: declining quantities in aerosols and other uses that result in short term emissions, and increasing importance of the bank of blowing agent contained in closed cell foams, the preexisting emission functions have now become inadequate. The dominance by prompt sources, until recently, accounts for the acceptable fit up to the 1980s. However, this does not explain why the previous emission function from foam blowing gave such a good fit until the early 1990s and such a poor fit thereafter. The only difference between the calculated concentrations is in the treatment of the foam emissions; all other emissions, including the prompt and short term releases from refrigeration, are treated the same way in both calculations. This implies that the emission functions for prompt and short term releases are as valid now as they were during the 1970s and 1980s; an important result because of the implications for the newer refrigerants used in similar applications and equipment. Several changes to the way that fluorocarbon blowing agents are emitted from foams occurred in recent years and the emission functions developed from the market survey (Ashford, 1999) reflect such developments in
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improving the containment of blowing agents. It is not clear how long these changes have been effective; the earlier studies (McCarthy et al., 1977; Gamlen et al., 1986; Fisher and Midgley, 1994) indicated that there had been no identifiable change in emissions functions up to the late 1980s while Ashford (1999) shows a clear change by the mid-1990s. Within these spans of time, each set of emissions functions, coupled with a constant atmospheric lifetime, gives calculated atmospheric concentrations that match the observations. In reality the transition from the old practices to better containment occurred over several years and the effect of this on emissions would extend for even longer. However, the new emission function from foams is consistent with recent atmospheric measurements, suggesting that the transition to new practices is effectively complete. Changing from old to new emissions functions in 1993 gives a good fit to the observations. Undoubtedly this oversimplifies the situation but it affects the calculations for less than 10 yr within the late 1980/early 1990 timeframe and the effect is much less than the uncertainty estimate. The recommended emissions (based on the best fit, as described here) and their 2s uncertainties are shown in Table 4. It is recommended that the new function is used to calculate emissions of CFC-11 and other fluorocarbon foam blowing agents from the early 1990s onwards. For the newer agents that would mean that the new function should be used for the whole of their product lifetimes. No change to the emission functions for prompt and short term releases is justified. Acknowledgements The market survey and the development of revised emission functions were commissioned and financially supported by the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS).
References AFEAS (Alternative Fluorocarbons Environmental Acceptability Study), 2000. Production, sales and atmospheric release of fluorocarbons through 1998, published at www.afeas.org by AFEAS, Rand ES&P Centre, 1200 South Hayes St., Arlington VA, USA.
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Ashford, P., 1999. Development of a global emission function for blowing agents used in closed cell foam. Final Report to AFEAS (as above), by Caleb Management Services. Baker, J.A., 1999. Mobile air conditioning: HFC-134a emissions and emission reduction strategies. Proceedings of the Joint IPCC/TEAP Expert Meeting, Petten, The Netherlands, 26–28 May 1999. Fisher, D.A., Midgley, P.M., 1994. Uncertainties in the calculation of atmospheric releases of chlorofluorocarbons. Journal of Geophysical Research 99 (D8), 16643–16650. Gamlen, P.H., Lane, B.C., Midgley, P.M., Steed, J.M., 1986. The production and release to the atmosphere of CCl3F and CCl2F2 (Chlorofluorocarbons CFC-11 and CFC-12). Atmospheric Environment 20 (6), 1077–1085. March, 1992. CFCs in the UK refrigeration and air conditioning industries. UK Department of the Environment, March Consulting Group, October 1992. McCarthy, R.L., Bower, F.A., Jesson, J.P., 1977. The fluorocarbon–ozone theory I. Production and releaseF world production and release of CCl3F and CCl2F2 (fluorocarbons 11 and 12) through 1975. Atmospheric Environment 11, 491–497. Norton, F.J., 1967. Thermal conductivity and life of polymer foams. Journal of Cellular Plastics 23–37. Prinn, R.G., Weiss, R.F., Fraser, P.J., Simmonds, P.G., Cunnold, D.M., Alyea, F.N., O’Doherty, S., Salameh, P., Miller, B.R., Huang, J., Wang, R.H.J., Hartley, D.E., Harth, C., Steele, L.P., Sturrock, G., Midgley, P.M., McCulloch, A., 2000. A history of chemically and radiatively important gases in air deduced from ALE/GAGE/ AGAGE. Journal of Geophysical Reseach 105 (D14), 17751–17792. Prinn, R.G., Zander, R., 1999. Long-lived ozone-related compounds. Scientific Assessment of Ozone Depletion: 1998, World Meteorological Organization Global Ozone Research and Monitoring Project Report No. 44, WMO, Geneva, Switzerland (Chapter 1). Quinn, T., 1978. The use and emissions of chlorofluorocarbons in closed-cell plastic foams. Rand Corporation Report No. Rand/WN-10273-EPA. SORG (Stratospheric Ozone Review Group), 1990. Stratospheric ozone 1990. Third Report of the UK SORG, Department of the Environment, London, UK. UNEP (United Nations Environment Programme), 1999. Production and consumption of ozone depleting substances, 1986–1998. Published at www.unep.org/ozone/reports2.htm by the Ozone Secretariat, UNEP. UNEP, 2000. Indian CFC production projects verification mission. United Nations Environment Programme, Nairobi, Kenya, March 2000. Yu Bingfeng, Wu Yezheng, Wang Zhigang, 2000. Phase out and replacement of CFCs in China. International Institute of Refrigeration Bulletin (1), 3–11.
Historic emissions of fluorotrichloromethane (CFC-11) based on a market survey A. McCullocha,*, P. Ashfordb, P.M. Midgleyc b
a School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK Caleb Management Services, Grovelands House, Woodlands Lane, Bristol BS32 4JT, UK c M&D Consulting, Ludwigstrae 49, D-70771 Leinfelden Musberg, Germany
Received 13 December 2000; received in revised form 10 April 2001; accepted 27 April 2001
Abstract Releases of CFCs occur promptly from applications such as aerosol sprays, or over a period of several years from refrigeration and air conditioning or more slowly still from use as blowing agents for closed cell plastic foams. As a consequence of the Montreal Protocol, the emissions have fallen and their pattern is continuing to change. To help quantify these changes the emissions from closed cell foam blowing have been re-examined in a comprehensive market survey, developing a lifecycle assessment for each foam type, production method and foaming agent. The original model for the time series of emissions from foam applications was shown to remain a robust representation in general terms. There is an ‘‘immediate’’ loss when the foam is manufactured, a slow emission from the foam itself during use and a loss on disposal of the artefact made with the foam. The original model used an initial loss rate of 10% and a subsequent loss of 4.5% yr1 over 20 yr. The new survey showed a wide range of initial and service loss rates. Immediate release ranges from 95% down to 4%; similarly, the rate of loss during service varies from 0.5% to 5% yr1 and the service lifetimes of the artefacts made with the foams varies from 12 to 50 yr. The apparent emission function, in terms of the mean value of the annual fractional release from the bank of CFC-11 residing in foams, was calculated from the survey to be 0.04370.008 over 28 yr. There is a small and non-significant fall in this function with time; so that over the last ten years of the data record the more appropriate value is 0.036670.0008. However, up to the early 1990s, it is the original emission function that is consistent with the observed atmospheric concentrations. Thenceforth this function seriously overpredicts the concentrations but, if the new emissions function for foams is used from 1993 onwards in conjunction with the original emission functions for all other uses, the fit becomes better. This suggests that the emission functions for prompt and short term releases remain valid and should be coupled with the new function to calculate emissions of CFC-11 or other fluorocarbon foam blowing agents from the early 1990s onwards. r 2001 Elsevier Science Ltd. All rights reserved. Keywords: Atmospheric concentration; Atmospheric lifetime; Foam blowing agent; Ozone depletion; Refrigerant
1. Introduction The Montreal Protocol has brought about an extensive reduction in the quantities of CFCs produced *Corresponding author. Present address: Marbury Technical Consulting, Barrymore, Marbury Road, Comberbach, Northwich CW9 6AU, UK. E-mail address: [email protected] (A. McCulloch).
and this is beginning to be reflected in falling atmospheric concentrations of materials such as CFC-11 (fluorotrichloromethane, CFCl3). The actual concentrations are related to the quantities emitted and the rate at which the material is removed from the atmosphere (its atmospheric lifetime). It is, therefore, possible to derive the atmospheric lifetime of a compound using data for the quantities emitted and measured atmospheric concentrations. This is one function of the advanced global atmospheric gases experiment (Prinn et al., 2000) which
1352-2310/01/$ - see front matter r 2001 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 0 1 ) 0 0 2 4 9 - 7
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uses emissions data for CFCs provided by the fluorocarbon industry (McCarthy et al., 1977; Gamlen et al., 1986; AFEAS, 2000). However, while historic productions are known accurately, the emissions calculated from them currently rely on functions developed some time ago and are much less certain. In many end uses, simple emission functions developed from information provided by chemical manufacturers are still valid and have been verified by independent market surveys. Thus emissions of aerosol propellants, open cell foam blowing agents and solvents are prompt and so can be assigned accurately in time. At least half of the quantity used is released in the year of manufacture and the remainder within the following year. The short delay allows for stockholding of materials in transit, at the industries using them and by the final customer. Refrigerants are released over the service life of the equipment: on average, 3–5 yr for the major uses in large industrial installations and automotive air conditioning, a characteristic time confirmed by a number of studies (Gamlen et al., 1986; March, 1992; Baker, 1999). However, emissions from closed cell foams present a more complex case with different matricesFpolyurethane, polystyrene and polyalkenes, for exampleFand different surface finishes with different gas permeabilities; all of which influence release patterns. The emissions functions for foam blowing originally developed by McCarthy et al. (1977), although relatively crude, allowed for an initial loss of blowing agent and thence loss at a constant rate throughout the service life until all of the agent had been released. They were applied to all sales of a particular CFC into closed cell foam blowing and have survived several re-examinations by the chemical manufacturers. However, since emissions have begun to fall as a consequence of the Montreal Protocol, the calculated concentrations no longer match the observations. Accordingly, the current practices and consequent releases from closed cell foam blowing have been re-examined in a comprehensive market survey (Ashford, 1999) and the results have been tested against observations of atmospheric concentrations. The main principle of the test is that the shape of the concentration trend generated from emissions data is relatively insensitive to assumptions about atmospheric lifetime or the absolute level of production and so may be used to assess the reliability of emission functions that have been developed independently. This paper describes the development of a global database for production and sales of CFC-11 and the tests applied to the emission functions of McCarthy et al. (1977) and Ashford (1999).
2. A global database of CFC-11 production 2.1. Calculation of the annual production quantities of all CFCs The alternative fluorocarbons environmental acceptability study (AFEAS), following on from studies conducted by the chemical manufacturers’ association (CMA), records audited production of CFCs and HCFCs in all of the developed and much of the less developed world (Argentina, Australia, Brazil, Canada, France, Germany, Greece, Italy, Japan, Mexico, Netherlands, South Africa, Spain, UK, USA and Venezuela) (AFEAS, 2000). However, similar data for China, Czech Republic, India, Korea (both North and South), Taiwan, Romania and Russia are not reported in this way. There are three other sources of time-series data for the additional production: McCarthy et al. (1977), Gamlen et al. (1986) and UNEP (1999), and a selfconsistent database needs to be constructed from the four sets of numbers. Production prior to 1986: For these early years, Gamlen and colleagues show reported sales of CFCs 11 and 12 together with estimates of additional sales, from countries not reporting to the industry survey (socalled ‘‘non-reporting countries’’). For the purposes of this calculation, sales can be taken to be equal to production. However, in the period from 1968 to 1975, when this estimate of additional sales overlaps with the estimate of additional production of CFCs 11 and 12 by McCarthy et al. (1977), the data do not agree; neither the absolute values nor the relative productions, one to the other, match. The remainder of the data in Gamlen et al. are identical to those in the latest AFEAS compendium and, to promote consistency, the values in McCarthy et al. (1977) were not used. The Gamlen data cover the period from 1968 (when production in non-reporting countries was essentially zero) to 1982 and were extended to commencement of the UNEP data in 1986 by linear interpolation. Production from 1986 to 1998: Annual CFC production from 1986 onwards, for each country individually, is recorded in UNEP (1999). These data are expressed as ODP tonnes and do not discriminate individual CFCs. However, it is possible to verify the AFEAS data (reported by manufacturers and audited) against the aggregate of data reported to UNEP by the authorities in the countries of the AFEAS list (shown above). On a common basis, the two sets of data agree year-by-year to within 1% over the period 1986–95. Given this consistency, the level of confidence in the remainder of the UNEP data should be similar. The ‘‘additional’’ production for the period 1986–97 that was not reported to AFEAS was taken directly from UNEP (1999) and is shown in Fig. 1. The 1998 data were obtained as a personal communication from Adila, UNEP, Kenya, 2001.
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The CFC-12 fraction of this residue follows a trend opposite to that of CFC-113, with a reduction towards 1990 at 0.0098 yr1 (R2 ¼ 0:93) and a subsequent increase at 0.04 yr1 (R2 ¼ 0:89). Applied to the additional production, this gives an estimate of the CFC-12 component and, by difference, the CFC-11. From the AFEAS database itself, the variance between the production of CFC-11 calculated in this way and the recorded actual production is 1.5%; this was used subsequently as a measure of uncertainty. From 1982 to 1986, the data were linearly interpolated between the estimate of Gamlen et al. (1986) and the results of the calculation described. The reported, audited CFC-11 production and estimate of additional production from 1950 to 1999 are shown in Table 1.
Fig. 1. Additional production of CFCs not included in the AFEAS database. The dashed line indicates the long term trend.
The composite data set for all CFCs was constructed from the AFEAS data, augmented with the additional production from Gamlen et al. (1986) and UNEP (1999).
2.2. Calculation of the quantity of CFC-11 produced Up to 1982, the values estimated for ‘‘non-reported’’ production of CFC-11 in Gamlen et al. (1986) were used. From 1986 onwards, the parties to the Montreal Protocol report this additional production to the United Nations Environment Programme, allowing a potentially more robust estimate of recent production. Unlike the manufacturers’ database, which discriminates individual CFCs, the UNEP data describe production of all CFCs together, expressed as ODP tonnes. Essentially the compilation comprises dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113) and CFC-11. It is assumed that the global proportions of these are the same as those recorded by AFEAS. This is consistent with the production reported by India (for 1999 only) in UNEP (2000) and the consumption reported for China (for 1997 only) in Yu Bingfeng et al. (2000). In the AFEAS database, the CFC-113 fraction follows two distinct trends: an increase to 1990 at 0.0136 yr1 (R2 ¼ 0:96) and a decrease thereafter at 0.0295 yr1 (R2 ¼ 0:89). The same distribution was applied to the additional production reported in UNEP (1999). After correcting the difference in ODP (0.8 for CFC-113 and unity for the others), the residue to be divided between CFCs 11 and 12 was calculated.
2.3. Calculation of quantities used for foam and for other categories Historically, CFC-11 was used principally in aerosol propellant mixtures, a totally emissive end use with a prompt release pattern. The next most significant use was to blow closed cell plastic foams, primarily destined for insulation applications where the service life of the product is measured in decades and the leakage rate during service is relatively small. In the AFEAS data, use in closed cell foam blowing is recorded from 1950 onwards; up to 1976 to the nearest 105 kg yr1 and thenceforward to the nearest 103 kg yr1. From these, the fractional use of CFC-11 in all forms of closed cell foam blowing can be calculated for the production reported to AFEAS. This fraction varies significantly from one year to the next, with an arithmetic mean of 0.35 and a distribution skewed towards values below the mean. There is also a wide spread in the absolute quantities from which the fractions are derived; from 4000 to 170,000 tonne yr1, with many of the larger fractional uses coinciding with large absolute quantities. The sales weighted average fraction for CFC-11 use in foams is 0.41, with a standard deviation of 0.41. There is no information on end use in the UNEP data and so the usage of CFC-11 in closed cell foam in the additional production was assumed to be the same as that in the AFEAS-reported production. This could be based on individual annual values or on a mean. The annual values exhibit wide swings, especially in recent years as the exigencies of the Montreal Protocol have become apparent and there is no reason to suppose that the large interannual variations in reported use outside of India, China and Russia should also be shown by their additional use. For the total CFC-11 use in closed cell foam, the difference between calculations using the sales-weighted average fraction (0.41) from the AFEASreported data and the individual annual values is 0.3% (RMS average). The sales weighted average was used to
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Table 1 Global production of CFC-11 and sales into closed cell foam
Year
1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Production (sales) reported to CMA or AFEAS
Additional production (sales)
CFC-11 (all uses) 103 kg
CC foam component 103 kg
CFC-11 (all uses) 103 kg
6623 9072 13562 17282 20911 26263 32477 33929 29529 35562 49714 60464 78109 93304 111085 122833 141022 159756 183116 217271 238136 263175 306856 349085 369724 314068 339832 320464 308852 289483 289619 286943 271443 291731 312355 326814 350148 382050 375986 302489 232916 213486 186434 147131 60232 32683 22123 18577 14600 12871
93 127 190 242 293 368 455 590 635 953 2087 2767 5670 8255 11158 13426 16828 19731 25401 31661 34156 42547 51710 62051 61916 55474 52073 65227 66089 80105 84051 97704 94937 97985 110638 117343 129618 160085 165982 164219 144438 148034 137941 106792 35109 14259 4186 6818 6777 7824
0 1000 2000 3000 4000 4900 7300 9900 12200 12500 14100 17500 20400 23100 38612 40437 42274 44111 44907 46846 48757 50640 50542 45788 37409 33238 41764 40831 31363 33113 31708 31487
Total quantity of CFC-11 used in CC foam
CC foam component 103 kg
103 kg
0 410 820 1230 1640 2009 2992 4058 5001 5124 5780 7173 8362 9469 15827 16575 17328 18081 18408 19202 19986 20757 20717 18768 15334 13624 17119 16737 12857 13573 12997 12906
93 127 190 242 293 368 455 590 635 953 2087 2767 5670 8255 11158 13426 16828 19731 25401 32071 34975 43777 53349 64060 64908 59532 57074 70351 71869 87278 92413 107173 110764 114560 127966 135424 148026 179287 185968 184976 165155 166802 153275 120416 52228 30996 17043 20391 19774 20730
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calculate the values reported in Table 1 and the difference was treated as a variance.
3. Emissions from foams 3.1. Physical factors affecting emissions functions CFC-11 was used to blow a number of plastic matrices but most of the closed cell foams (i.e. those that retain the blowing agent within the cells) were blown in polyurethane. These foams are rigid, unlike open cell foams, such as those used in furniture. The low thermal conductivity of CFC-11, conferred in part by its high molecular weight, meant that its foams were good thermal insulators. They were produced in a variety of forms: for domestic refrigerators, for example, the foam was blown in situ in the space between the outer shell (generally steel) and the food storage cabinet (generally plastic) and advantage was taken of the rigidity conferred by the foam itself in the structural integrity of the units. Foam in this sort of application was effectively contained within gas-impervious facings. At the other extreme, slabs used for building insulation were generally cut from a larger block of foam. In this form all surfaces of the foam were exposed to the atmosphere. Blowing agent is released into the atmosphere at three stages in the life of the foamFduring manufacture of the foam, during disposal at the end of its service life and during use, when the loss is generally small and slow. Typically, losses during manufacture occur from evaporation of the blowing agent before it becomes incorporated into the foam or from the scrap that is trimmed from foams that are blown as slabs. In many cases the plastic in the scrap foam may be recovered but the blowing agent is lost. Losses during use are thought to arise from slow migration of the blowing agent by dissolution in the matrix and re-evaporation to atmosphere (Norton, 1967). Potentially, material that is still in the foam at the end of its life may be recovered but this was seldom practiced for articles made with CFC blown foam (Quinn, 1978). 3.2. Original emission function (CMA and AFEAS) For the original emission function and as a result of examining the way that CFC foams were blown in the early 1970s, the CFC manufacturers decided that initial losses during foam manufacture were best represented by a single loss of 10%. The average service life of the foam, both as a board and as part of an article was estimated to be 20 yr and the remainder of the blowing agent was assumed to leak from the foam at a constant rate of 4.5% of the original quantity per year (McCarthy et al., 1977). This accounted for both the losses in service
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and on disposal. Clearly it is an oversimplification; foam contained between impervious facings is unlikely to have the same loss rate as board open to the atmosphere and the range of service lifetimes is much broader than that indicated by a single value of 20 yr. Nevertheless, the algorithm survived re-examination in the 1980s (Gamlen et al., 1986) and early 1990s (Fisher and Midgley, 1994). One reason for the longevity of this emission function is that it matches well with the way that manufacturers collect data (AFEAS, 2000). Audited sales are subdivided for each compound into end uses and there is a single category for all closed cell foam applications. Whatever emissions functions are adopted in the future, the historic data cannot now be reconstructed into more specific categories. It is unlikely that the fluorocarbon manufacturers could supply audited information for use in specific types of foam, even from now on. Such information may reside in the records of foam manufacturers but the number of manufacturers is too large to expect to obtain complete audited data year by year. However, a single comprehensive survey of the foam manufacturers should give a better view of current practices and the expectations for future emissions than the rather elderly information now in use. 3.3. New functions for foam manufacturing sectors During 1997 and 1998, a comprehensive global survey of foam manufacturing was carried out by Caleb Management Services (Ashford, 1999). This centred around interviews with key foam producers (35 interviews were conducted), coupled with data from technical literature and trade associations. The manufacturing sectors covered were: Polyurethane (PU) also known as polyisocyanurate (PIRA) integral skin foam, PU rigid insulation foams, used in or manufactured as: continuous and discontinuous panels; appliances and other systems blown in situ; continuous and discontinuous block; spray; continuous flexibly faced laminate. Extruded polystyrene foams Polyethylene foams, as: board; pipe. Phenolic foams, as: continuous flexibly faced laminate; discontinuous block. Each of these potentially has its own emission pattern and may involve the use of one or more CFC, HCFC or HFC. The compounds that were considered comprised
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CFCs 11 and 12, HCFCs 22, 141b and 142b and HFC134a; only CFC-11 is discussed in detail here. From the results of the interviews within the relevant industry sectors, a lifecycle assessment for current practice for each foam type, production method and foaming agent was developed. These were refined by cycling through a peer review process with the original interviewees and the UNEP technical options committee for foams. The general model for the time series of emissions from the foam applications was shown to remain a robust representation. There is an ‘‘immediate’’ loss when the foam is manufactured, a slow emission from the foam itself during use and a loss on disposal of the artefact made with the foam. The survey showed a wide range of initial and service loss rates. The immediate release ranges from 95% down to 4%; similarly, the rate of loss during service varies from 0.5% to 5% yr1 and the service lifetimes of the artefacts made with the foams varies from 12 to 50 yr. Surprisingly in view of the physical process by which the blowing agent dissolves out of the foam, losses are relatively insensitive to the nature of the blowing agent; the properties of the plastic matrix and the mechanics of the foam forming process are much more important. The complete set of loss parameters, together with their 1s uncertainties, is shown in Table 2.
construction rubble is landfilled. Only if the plastic foam is thermally oxidised in a properly operated incinerator will the blowing agent be destroyed; casual uncontained burning is likely to disrupt the plastic matrix allowing the blowing agent to escape without being properly oxidised. Historically, very little of the CFC-11 blown foam was incinerated (Quinn, 1978) and so total and immediate loss on disposal has been assumed for all of the applications at the end of their service life. 3.5. Quantities in each end use and total emissions from foams The market survey (Ashford, 1999) provided an independent estimate of the quantities of CFC-11 used in closed cell foam that agreed with the AFEAS data to within 7%. The data also quantified the annual use of CFC-11 in each type of foam, as shown in Table 3, and were used to distribute the total annual CFC-11 use (shown in Table 1) between foam applications. Then the annual global totals of emissions of CFC-11 from closed cell foams were calculated using the emissions functions for individual foam applications shown in Table 2. This estimate implies that the emissions functions are globally applicable; that the pattern of emissions in time depends only on the foam application and is independent of the geographical region where the CFC-11 is used.
3.4. Loss on disposal 4. Emissions from all categories When the appliance or building using the insulating foam becomes surplus to requirements the foam represents only a small part of the total disposal problem. Most commonly, the foamed plastic is not separated from the rest of the scrap and the residual blowing agent is released when appliances are crushed or
The AFEAS compendium (AFEAS, 2000) contains separate estimates for the emissions from aerosol propulsion (50% released immediately and 50% in the following year), open cell foam (83% released immediately and 17% in the following year) and refrigeration,
Table 2 Contemporary emission patterns from plastic foams
Application a
PU integral skin PU continuous panel PU discontinuous panel PU appliance PU blown in situ PU continuous block PU discontinuous block PU continuous laminate PU spray Phenolic laminate Phenolic block a
PU signifies polyurethane.
Fraction released
Fraction released
Service life of equipment
Initially
Uncertainty
Annually
Uncertainty
Years
Uncertainty
0.95 0.075 0.0125 0.04 0.06 0.35 0.4 0.1 0.25 0.1 0.4
0.0125 0.0125 0.0125 0.005 0.005 0.005 0.005 0.025 0.025 0.025 0.05
0.025 0.005 0.005 0.0025 0.0025 0.0075 0.0075 0.015 0.015 0.015 0.0075
0.00675 0.00125 0.00125 0.001 0.001 0.0015 0.0015 0.0025 0.0025 0.0025 0.0015
25 25 15 15 15 15 60 50 60 15
2.5 2.5 2.5 2.5 2.5 2.5 10 10 10 2.5
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A. McCulloch et al. / Atmospheric Environment 35 (2001) 4387–4397 Table 3 Distribution of CFC-11 consumption in closed cell foam blowing between foam types, expressed as percent of the total Year Polyurethane
1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Phenolic
Integral Continuous Discontinuous Appliance Blown Continuous Discontinuous Laminate Spray skin panel panel in situ block block
Laminate Block
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 2 4 6 8 10 11 12 12 12 12 12 12 12 12 12 11 9 6 5 3 2 1 1 1 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 3 5 6 7 7 7 8 7 7 7 6 6 6 7 8 9 9 9 9 9 10 8 9 10 10
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 10 12 17 17 16 15 14 13 12 11 10 9 8 8 8 8 8 8 8 7 7 6 7 7 8 8 8 8 8 9 13 18 24 31
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 6 11 17 20 20 20 20 19 19 19 19 19 19 20 21 23 24 25 26 26 27 28 29 30 32 37 44 40 35 30
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 12 13 16 16 14 12 11 10 9 8 8 7 7 6 6 6 6 6 5 5 5 5 5 6 7 8 10 12 13 13 10 8 7 5
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 3 3 2 3 3 4 3 3 3 3 3 3 3 3 3 2 2 2 3 3 3 3 2 2 2 1 0 0 0
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 82 62 42 27 19 11 8 7 6 5 5 4 4 4 4 4 4 3 3 3 3 3 2 2 3 3 3 3 2 2 2 1 1 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 16 33 39 46 47 47 43 41 39 37 35 33 33 33 33 33 32 33 33 33 34 33 32 30 27 26 25 23 20 12 6 4 2 2
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 2 3 5 6 7 8 8 8 8 8 8 8 8 7 7 7 7 8 9 10 10 10 12 14 16 19 21 22
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0
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which for CFC-11 is classed as all being non-hermetic. The rate of release from non-hermetic refrigeration is distributed approximately normally about a mean of 4.5 yr. Thus emissions in the first year are small, grow to a maximum at 4.5 yr and subsequently all of the refrigerant is estimated to be released within 10 yr of being charged into the equipment. This pattern reflects the fact that releases during the operation of nonhermetic refrigeration systems are significant and inherent in the design of the equipment. These releases were augmented by emissions calculated from the additional production not included in the AFEAS data but comprising part of the UNEP database, which was treated as being used in refrigeration and closed cell foam only. The total calculated annual emissions and the contributions from refrigeration, other uses (aerosol and open cell foams), additional refrigeration and closed cell foam blowing are shown in Table 4. Characteristically, the emission of blowing agent from closed cell foams is dominated by releases, both during operation and at end-of-life, from the insulation now installed. In the case of CFC-11 this is accentuated by the rapid decline in sales for closed cell foam in recent years, shown in Table 1. With little or no further addition to the bank and no change in the social factors acting on emissive practices, for example, legislation on recovery or destruction of blowing agent at end-of-life, the rate of emission should tend towards a constant fraction of the bank. Fig. 2 shows that the annual fraction of the bank in foams that is calculated to be emitted tended towards a constant value for the mature market. Over 28 yr, the rate of emission calculated in this way is approximately represented by the relationship in Eq. (1)
of 2 yr (Gamlen et al., 1986). Monte Carlo combination of the uncertainties for each of these end uses, assuming normal distributions and typical standard deviations, gave values for the coefficients of variation of each end use in each year. These were combined, weighted by the annual mean emissions, with the coefficients of variation in short term emissions (fugitive, aerosol and open cell foams) and additional production. For the short term emissions the uncertainty is 0.5%, which is essentially the uncertainty in the absolute quantity falling into this category, the rate of release having been shown to have no significant effect when emissions are accounted annually (Gamlen et al., 1986; Fisher and Midgley, 1994). The additional production is subject to several sources of uncertainty: a variance of 0.5% arises from uncertainty in the product mix, as described in Section 2.2 above, a variance of 0.3% arises from uncertainty in the calculation of the fraction used in closed cell foam and a further 1% accounts for the difference between the UNEP and AFEAS databases. Based on the contemporary emission functions, the emissions and combined annual uncertainties at 2s are shown in Table 4.
R ¼ 0 0613 0 000534T;
Cy ¼ ST þ ðCy1 STÞexpð1=TÞ;
ð1Þ
where R is the annual fraction of the bank released and T is the year number, with zero in 1950 in this case. The coefficient of variance (R2 ) for this line is only 35%, suggesting that the slope cannot be considered significant and the mean value over this period (0.04370.008) is a valid description of the calculated release rate. Nevertheless, the better description of the more recent emission function, over the last 10 years of the data record, is somewhat lower at 0.036670.0008.
5. Uncertainty Uncertainty in the calculated emissions from foams arises from uncertainties in the quantity lost initially, in the annual losses and in the lifetime over which the losses occur, as shown in Table 2. Losses from refrigeration are calculated as described in Section 4 above using a normal distribution about a mean lifetime of the equipment; in this case, 4.5 yr, with an uncertainty
6. Calculated atmospheric concentrations Fig. 3 shows the average tropospheric concentrations of CFC-11 calculated from the new emissions over the whole database for atmospheric lifetimes of 52, 40 and 76 yr; representing, respectively, the mean and the extremes of the optimal estimation of lifetime as described in Prinn et al. (2000). The concentrations were estimated at yearly intervals using the formula in Eq. (2) (SORG, 1990). ð2Þ
where Cy and Cy1 are the average atmospheric concentrations in a year and in the previous year, S is the emission during the year and T is the average atmospheric lifetime in years. According to the Scientific Assessment of Ozone Depletion, 1998 (Prinn and Zander, 1999; Prinn et al., 2000), the atmospheric concentration of CFC-11 levelled off in the mid-1990s and has begun to decrease. The shapes of the curves in Fig. 3 agree in a general sense with that observation, but the rate of decline in measured tropospheric concentrations is greater than that calculated (even at the shortest lifetime) and the measurements up to 1990 are matched only by calculations using the longest lifetime. The shape of the observed concentration curve cannot be matched by changing only the lifetime. The recommended atmospheric lifetime for CFC-11, based on calculations using a number of modelling techniques that go beyond the mass balance described in Prinn et al. (2000), is 4577 yr (Prinn and Zander, 1999).
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A. McCulloch et al. / Atmospheric Environment 35 (2001) 4387–4397 Table 4 Calculated global emissions of CFC-11 based on a combination of contemporary and historic emission functions Global emissions of CFC-11 Year
1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Sectorial emission (from AFEAS data)
Additional emission (this work)
Refrigeration (106 kg)
Other (106 kg)
Refrigeration (106 kg)
CC foam (106 kg)
0.22 0.24 0.31 0.43 0.59 0.79 1.02 1.32 1.69 2.11 2.64 3.24 3.86 4.53 5.18 5.81 6.49 7.17 7.89 8.72 9.61 10.6 11.7 13.1 14.5 15.8 17.6 19.0 20.6 22.5 24.3 25.9 26.8 27.4 27.1 26.7 26.1 25.9 26.2 26.5 26.7 26.5 25.5 23.7 21.4 19.0 16.5 14.0 11.6 9.2
5.25 7.37 10.6 14.5 17.9 22.1 27.6 30.7 28.3 28.5 37.4 48.2 60.3 73.6 87.1 99.0 110 125 141 164 186 202 227 258 283 269 271 253 228 201 183 172 159 167 180 185 194 200 197 141 89.2 56.3 37.6 27.2 17.8 10.4 10.6 7.6 4.6 4.0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.04 0.14 0.32 0.56 1.02 1.57 2.25 3.08 3.99 5.01 6.12 7.25 8.45 10.3 12.4 15.0 17.9 20.6 22.9 24.7 26.1 27.1 27.8 27.9 27.4 26.6 25.3 23.9 22.9 22.0 21.1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.08 0.15 0.22 0.29 0.36 0.60 0.96 1.37 1.48 1.89 2.37 2.93 3.26 5.65 5.84 6.03 6.39 6.43 6.72 7.31 7.90 8.12 7.00 5.81 6.36 16.3 28.1 39.0 37.7 38.4 38.1
AFEAS CC foam emission 6 (10 kg)
Using AFEAS emission function (106 kg)
Using new emission function throughout (106 kg)
Recommended value (106 kg)
0.01 0.02 0.04 0.05 0.07 0.10 0.13 0.17 0.20 0.28 0.49 0.68 1.24 1.87 2.68 3.50 4.62 5.79 7.54 9.58 11.4 14.2 17.4 21.3 24.0 25.8 27.7 32.1 35.0 40.1 44.0 49.9 53.3 57.9 63.5 69.0 75.1 84.7 91.4 97.5 100 106 108 107 98.3 94.4 91.1 89.0 86.0 83.1
5.49 7.63 11.0 15.0 18.6 23.0 28.7 32.2 30.2 30.9 40.5 52.1 65.4 80.0 95.0 108 121 138 157 182 207 227 257 294 324 314 321 309 291 272 261 260 255 271 292 305 322 340 347 299 251 223 205 192 181 178 182 172 164 156
5.44 7.74 11.0 15.0 18.6 23.2 28.7 32.2 30.3 31.0 41.0 52.6 66.5 81.5 97.0 110 122 137 154 178 202 221 248 284 312 301 308 296 277 258 246 243 236 248 267 278 292 312 316 264 208 173 149 134 112 100 95.6 88.3 81.3 76.4
5.5 7.6 11.0 15.0 18.6 23.0 28.7 32.2 30.2 30.9 40.5 52.1 65.4 80.0 95.0 108.3 121.3 137.6 156.8 182.0 206.9 227.5 256.6 293.8 323.6 314.1 321.1 309.4 290.5 272.1 261.0 259.9 255.4 271.0 292.1 305.1 322.1 340.3 346.5 299.2 251.3 223.2 205.0 191.9 111.9 100.3 95.6 88.3 81.3 76.4
Using the mean mass balance lifetime of 52 yr and the new emissions functions, concentrations calculated for the whole of the time that CFC-11 has been emitted into the atmosphere seriously understate
Uncertainties (106 kg) +2s
2s
6.0 8.2 11.5 15.5 19.2 23.8 29.6 33.2 31.5 32.4 42.3 54.2 67.6 82.5 97.6 111.0 124.2 140.7 160.0 185.6 210.9 231.9 261.7 299.8 330.2 320.1 328.7 317.2 299.0 281.3 269.9 268.0 263.8 279.3 300.8 313.7 331.3 351.5 360.8 313.3 263.8 235.9 219.6 208.9 125.7 116.4 113.3 106.6 100.4 98.4
5.0 7.1 10.5 14.4 17.9 22.3 27.9 31.1 28.8 29.4 38.8 50.1 63.1 77.6 92.4 105.6 118.3 134.5 153.6 178.4 202.9 223.1 251.5 287.8 317.0 308.2 313.6 301.6 282.0 263.0 252.2 251.9 247.1 262.8 283.4 296.5 312.9 329.0 332.2 285.1 238.9 210.5 190.5 174.9 98.1 84.3 78.0 69.9 62.3 54.5
the observed values. A difference of only 2 pmol mol1 in 1980, rises through 10 in 1985 to reach 20 pmol mol1 in 1990. These differences are statistically significant at 2s:
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Fig. 2. Calculated fraction of the bank of CFC-11 retained in foams that is released annually. The trend from 1970 onwards quantified in Eq. (1) is shown as the dotted line.
Fig. 4. Atmospheric concentrations of CFC-11 calculated using the AFEAS emission functions throughout (dashed line) and the AFEAS functions for foam emissions to 1993 and the new function thereafter (solid line). The dotted lines show uncertainties at 2s and measured concentrations are shown as filled squares.
the new emissions function for foams is used from 1993 onwards in conjunction with the original emission functions for all other uses, the fit becomes better.
7. Conclusions
Fig. 3. Atmospheric concentrations of CFC-11 calculated with the new emission functions using atmospheric lifetimes of 40, 52 and 76 yr. The dotted lines show uncertainties at 2s and the filled squares are the observed concentrations.
Not surprisingly, the concentrations calculated from the AFEAS emission function using the mean mass balance lifetime are in much better agreement with measurements up to 1990. Fig. 4 shows the global average of the measured concentrations as reported by Prinn et al. (2000) and the concentrations calculated from the original AFEAS data (AFEAS, 2000) (with allowance for emissions from additional production) using the original emission functions (Gamlen et al., 1986) and the mean lifetime of 52 yr. Up to the early 1990s, the fit is good but thenceforth these emissions seriously overpredict the atmospheric concentration. If
With the change in use pattern of CFC-11: declining quantities in aerosols and other uses that result in short term emissions, and increasing importance of the bank of blowing agent contained in closed cell foams, the preexisting emission functions have now become inadequate. The dominance by prompt sources, until recently, accounts for the acceptable fit up to the 1980s. However, this does not explain why the previous emission function from foam blowing gave such a good fit until the early 1990s and such a poor fit thereafter. The only difference between the calculated concentrations is in the treatment of the foam emissions; all other emissions, including the prompt and short term releases from refrigeration, are treated the same way in both calculations. This implies that the emission functions for prompt and short term releases are as valid now as they were during the 1970s and 1980s; an important result because of the implications for the newer refrigerants used in similar applications and equipment. Several changes to the way that fluorocarbon blowing agents are emitted from foams occurred in recent years and the emission functions developed from the market survey (Ashford, 1999) reflect such developments in
A. McCulloch et al. / Atmospheric Environment 35 (2001) 4387–4397
improving the containment of blowing agents. It is not clear how long these changes have been effective; the earlier studies (McCarthy et al., 1977; Gamlen et al., 1986; Fisher and Midgley, 1994) indicated that there had been no identifiable change in emissions functions up to the late 1980s while Ashford (1999) shows a clear change by the mid-1990s. Within these spans of time, each set of emissions functions, coupled with a constant atmospheric lifetime, gives calculated atmospheric concentrations that match the observations. In reality the transition from the old practices to better containment occurred over several years and the effect of this on emissions would extend for even longer. However, the new emission function from foams is consistent with recent atmospheric measurements, suggesting that the transition to new practices is effectively complete. Changing from old to new emissions functions in 1993 gives a good fit to the observations. Undoubtedly this oversimplifies the situation but it affects the calculations for less than 10 yr within the late 1980/early 1990 timeframe and the effect is much less than the uncertainty estimate. The recommended emissions (based on the best fit, as described here) and their 2s uncertainties are shown in Table 4. It is recommended that the new function is used to calculate emissions of CFC-11 and other fluorocarbon foam blowing agents from the early 1990s onwards. For the newer agents that would mean that the new function should be used for the whole of their product lifetimes. No change to the emission functions for prompt and short term releases is justified. Acknowledgements The market survey and the development of revised emission functions were commissioned and financially supported by the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS).
References AFEAS (Alternative Fluorocarbons Environmental Acceptability Study), 2000. Production, sales and atmospheric release of fluorocarbons through 1998, published at www.afeas.org by AFEAS, Rand ES&P Centre, 1200 South Hayes St., Arlington VA, USA.
4397
Ashford, P., 1999. Development of a global emission function for blowing agents used in closed cell foam. Final Report to AFEAS (as above), by Caleb Management Services. Baker, J.A., 1999. Mobile air conditioning: HFC-134a emissions and emission reduction strategies. Proceedings of the Joint IPCC/TEAP Expert Meeting, Petten, The Netherlands, 26–28 May 1999. Fisher, D.A., Midgley, P.M., 1994. Uncertainties in the calculation of atmospheric releases of chlorofluorocarbons. Journal of Geophysical Research 99 (D8), 16643–16650. Gamlen, P.H., Lane, B.C., Midgley, P.M., Steed, J.M., 1986. The production and release to the atmosphere of CCl3F and CCl2F2 (Chlorofluorocarbons CFC-11 and CFC-12). Atmospheric Environment 20 (6), 1077–1085. March, 1992. CFCs in the UK refrigeration and air conditioning industries. UK Department of the Environment, March Consulting Group, October 1992. McCarthy, R.L., Bower, F.A., Jesson, J.P., 1977. The fluorocarbon–ozone theory I. Production and releaseF world production and release of CCl3F and CCl2F2 (fluorocarbons 11 and 12) through 1975. Atmospheric Environment 11, 491–497. Norton, F.J., 1967. Thermal conductivity and life of polymer foams. Journal of Cellular Plastics 23–37. Prinn, R.G., Weiss, R.F., Fraser, P.J., Simmonds, P.G., Cunnold, D.M., Alyea, F.N., O’Doherty, S., Salameh, P., Miller, B.R., Huang, J., Wang, R.H.J., Hartley, D.E., Harth, C., Steele, L.P., Sturrock, G., Midgley, P.M., McCulloch, A., 2000. A history of chemically and radiatively important gases in air deduced from ALE/GAGE/ AGAGE. Journal of Geophysical Reseach 105 (D14), 17751–17792. Prinn, R.G., Zander, R., 1999. Long-lived ozone-related compounds. Scientific Assessment of Ozone Depletion: 1998, World Meteorological Organization Global Ozone Research and Monitoring Project Report No. 44, WMO, Geneva, Switzerland (Chapter 1). Quinn, T., 1978. The use and emissions of chlorofluorocarbons in closed-cell plastic foams. Rand Corporation Report No. Rand/WN-10273-EPA. SORG (Stratospheric Ozone Review Group), 1990. Stratospheric ozone 1990. Third Report of the UK SORG, Department of the Environment, London, UK. UNEP (United Nations Environment Programme), 1999. Production and consumption of ozone depleting substances, 1986–1998. Published at www.unep.org/ozone/reports2.htm by the Ozone Secretariat, UNEP. UNEP, 2000. Indian CFC production projects verification mission. United Nations Environment Programme, Nairobi, Kenya, March 2000. Yu Bingfeng, Wu Yezheng, Wang Zhigang, 2000. Phase out and replacement of CFCs in China. International Institute of Refrigeration Bulletin (1), 3–11.