Review of Methyl chloroform Distributed Emissions from the Global Emissions Inventory Activity (GEIA)

Methyl chloroform (CCl3CH3, 1,1,1-trichloroethane) was primarily used as a
solvent in a wide range of industrial and commercial processes from which
emissions occur much more promptly than from, for example, refrigeration
systems. Because most purchases were made to replace material that had already
been emitted, emissions are an effectively invariant function of sales.
Incorporating delays in the supply chain and the average delay between purchase
of the material by the user and its emission, 75% of the material is emitted in
the year of purchase and 25% in the following year (Midgley and McCulloch,
1995). Similar functions were applied to the relatively small quantities of
methyl chloroform that were recently stockpiled. Simple delays, of one and two
years, were used to account for the stock holding times.

Audited production and sales of methyl chloroform are subdivided into
geographical regions in the industrial database. This enabled sales to be
assigned to countries on the basis of each national share of the total regional
Gross Domestic Product, as described in Midgley and McCulloch (1995). This use
of relative GDP as a distribution function was shown to be valid for
fluorocarbon solvents in McCulloch et al. (1994). Within each country,
emissions were assigned to gridsquares using the population distribution in Li
(1996).

Results are presented here as the percentage distribution among gridsquares.
Absolute emission from each gridsquare in 1990 should be calculated by
multiplying global emission for 1990 in Table 1 by the gridsquare percentages
in Table 2(Keene et al., 1999). For other years, the distribution in Table 2
(download
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 1985 to 1995 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.
Based on McCulloch and Midgley (2001) the time series (1951 to 2000) of methyl
chloroform emissions and their uncertainties is shown in Table 1
(http://geiacenter.org/ reviews/mcfTabl1.html).

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 to take account of the significant reduction in productive
capacity that has occurred in recent years and will be published in Fraser and
Montzka (2003).