A. McCulloch

Emission Functions

CFC-12 (CCl₂F₂, dichlorodifluoromethane) is now used primarily within refrigeration and air conditioning systems as the working fluid. Some material is released into the atmosphere when these systems are first filled but the bulk of the losses occur subsequently during maintenance, or as the result of accidental damage or when the equipment is finally removed from service and scrapped. There are other minor uses in foam blowing 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. (2002).

Releases from hermetic refrigeration are normally distributed about an average of 10 years, so that complete emission occurs within 20 years. The emission function for non-hermetic refrigeration is faster, with an approximately normal distribution about a 4.5 year mean and complete emission within 10 years. Due to the nature of the plastic foam matrices, half of the material used in closed cell foam is emitted in the year of manufacture and half in the following year. 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.

These data sets have been amalgamated to provide global consumption values with defined quality and uncertainty and the distributed emissions described here were based on McCulloch et al. (1994).

Geographical Distribution of Emissions

The calculated global emissions of CFC-12 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 (CFC12EM) by the gridsquare percentages in Table 2 (CFC1286yr1.1a). 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

Taken from McCulloch et al., 2002 (itself compiled from AFEAS, 2001 and UNEP, 2002), the time series (1930 to 2000) of CFC-12 emissions and their uncertainties is shown in Table 1 .

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-12 was described in Madronich and Velders (1999). This scenario has been updated and will be published in Fraser and Montzka (2003).

Table

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).

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.

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.M. Midgley and P. Ashford, Releases of Refrigerant Gases (CFC-12, HCFC-22 and HFC-134a) to the Atmosphere, submitted to Atmospheric Environment, 2002.

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).