A. McCulloch

Emission Functions

CFC-11 (CCl₃F, trichlorofluoromethane) is now used primarily within rigid plastic insulating foams ("closed cell foams"). Some material is released into the atmosphere when the foam is first blown but most of the losses occur in the long term due to gradual migration of the insulating gas through the cell walls, with total loss when the equipment is finally removed from service and scrapped. There are other minor uses in refrigeration and historical use in aerosol propellant formulations.

As a consequence of the delay between first use and release, it is necessary to calculate emissions from time series of data on production and sales into various end-use categories having different release functions. The calculation method is described in McCulloch et al. (2001).

The rate of emission from closed cell foams varies with the nature of the plastic matrix. However, for most of the period over which emissions have occurred, the release has been parameterised by a single function covering all matrices: some 10% of the CFC-11 used was lost during the blowing process and the remainder was released linearly over 20 years (at 4.5%/year) (Gamlen et al., 1986). Since the early 1990s, it has become apparent that this is now overstating the release rate and a constant rate of loss (3.66%/yr) from the accumulated bank in such foams (with no additional initial loss) has been used since 1994 (Ashford, 2000 and McCulloch et al., 2001)

The emission function for refrigeration has an approximately normal distribution about a 4.5 year mean and complete emission within 10 years. The emission function for aerosols and others provides for 50% release in the year of manufacture and the rest in the year following and the corresponding value for open cell foam is 83% in the year of manufacture. Emissions do not depend on the season of the year.

Basic Data on Sales

There is no single data set for global sales of any of the fluorocarbons. That compiled by industry (AFEAS, 2001) is compound specific and audited to ensure quality control, but has incomplete geographical coverage; production in China, India, Korea and Russia is not included. The data on production and consumption (the latter equating to sales) compiled by the United Nations Environment Programme to verify the application of the Montreal Protocol are neither compound specific nor audited although they do cover all parties to the Protocol (UNEP, 2002). UNEP data are reported as the aggregate total of all CFCs in ODPtonnes (Ozone Depletion Potential multiplied by metric tonnes). Submissions by individual countries are incorporated into the UNEP database with no further checks and reported values have been revised, without explanation, several years after they were first submitted. Such changes have had a small effect on the CFC-11 data set, resulting in minor changes from the values published in McCulloch et al. (2001). Nevertheless, amalgamation of the data sets to provide global consumption values with defined quality and uncertainty was accomplished substantially as described in that work.

Geographical Distribution of Emissions

The calculated global emissions of CFC-11 were distributed among countries using the distribution of individual national fractions of the world total Gross Domestic Product, as described in McCulloch et al. (1994). Within each country, emissions were distributed to individual gridsquares using a population distribution from Harvard University (Jennifer Logan, personal communication).

Results are presented here as the percentage distribution among gridsquares. Absolute emission from each gridsquare in 1986 should be calculated by multiplying global emission for 1986 in Table 1 (CFC11EM) by the gridsquare percentages in Table 2 (CFC1186yr1.1a). For other years, the distribution in Table 2 should be applied to the global emission for the appropriate year. While global emissions change relatively rapidly, distribution is affected only by relative economic activity and population dynamics, which have slower rates of change with time. It is expected that the distribution can be applied to the years 1980 to 1990 without significantly increasing uncertainty but this has not been tested. It can be applied to years beyond this range only with caution and new distributions for more recent years are under development.

Time Series of Global Emissions

Based on McCulloch et al. (2001) the time series (1933 to 2000) of CFC-11 emissions and their uncertainties is shown in Table 1 . From the years 1986 to 2000, the values are slightly different from those reported in the literature. This is due to an unexplained change in the UNEP database between successive publications in 1996 and 2002 which altered the quantities not included in the AFEAS database. The maximum annual difference between the published data and that recorded here is 5% and the two data sets are not significantly different at the 95% confidence level.

Future emissions will be governed by the controls required by the Montreal Protocol and by the quantity of material currently in the "bank" (that is: material which is in use but has not yet been emitted). A scenario for future releases of CFC-11 was described in Madronich and Velders (1999). This scenario has been updated and will be published in Fraser and Montzka (2003).

Development

In view of the changes brought about by the Montreal Protocol, it is proposed to revise the distribution functions to provide gridded data for the year 2000.

A. McCulloch
University of Bristol, UK
mailing address:
Barrymore, Marbury Road, Comberbach, Northwich, CW9 6AU, UK
phone/fax: +44-1606-891604e-mail: archie@marbury.u-net.com

References

AFEAS (Alternative Fluorocarbons Environmental Acceptability Study) Production, Sales and Atmospheric Releases of Fluorocarbons through 2000, AFEAS, Arlington, VA, USA, 2001 (see www.afeas.org).

Ashford P., 2000, Development of a global emission function for blowing agents used in closed cell foam, Final Report to AFEAS (as above), Arlington, VA, USA, 2000.

Fraser P. and S. Montzka, Controlled Substances and Other Source Gases, Ch. 1 of Scientific Assessment of Ozone Depletion: 2002, in preparation, WMO, Geneva, 2003.

Gamlen P.H., B.C. Lane, P.M. Midgley and J.M. Steed, The production and release to the atmosphere of CCl3F and CCl2F2 (Chlorofluorocarbons CFC-11 and CFC-12), Atmos. Environ., 20(6), 1077-1085, 1986.

Madronich S. and G.J.M. Velders, Halocarbon Scenarios for the Future Ozone Layer and Related Consequences, Ch. 11 of Scientific Assessment of Ozone Depletion: 1998, World Meteorological Organization Ozone Research and Monitoring Project Report No 44, WMO, Geneva, 1999.

McCulloch A., P.M. Midgley and D.A. Fisher, Distribution of emissions of chlorofluorocarbons (CFCs) 11, 12, 113, 114 and 115 among reporting and non-reporting countries in 1986, Atmos. Environ., 28(16), 2567-2582, 1994.

McCulloch A., P. Ashford and P.M. Midgley, Historic Emissions of fluorotrichloromethane (CFC-11) based on a market survey, Atmos. Environ., 35, 4387-4397, 2001.

UNEP (United Nations Environment Programme), Production and Consumption of Ozone Depleting Substances, 1986-2000, Secretariat to the Montreal Protocol, UNEP, Nairobi, Kenya, 2002 (see www.unep.org/ozone).