Methodological issues 7221 Choice of method

Historically, emissions from solvent applications generally have been considered prompt emissions because 100 percent of the chemical is typically emitted within two years of initial use. (IPCC, 2000). In order to estimate emissions in such cases, it is necessary to know the total amount of each HFC or PFC chemical sold in solvent products each year. Emissions of HFCs and PFCs from solvent use in year t can be calculated as follows.

Equation 7.5 Emission estimation method for solvent uses

Where:

Emissionst = emissions in year t, tonnes St = quantity of solvents sold in year t, tonnes St-1 = quantity of solvents sold in year t-1, tonnes

EF = emission factor (= fraction of chemical emitted from solvents in the year of initial use), fraction

Dt-1 = quantity of solvents destroyed in year t-1, tonnes

Table 7.1 indicates the known HFCs and PFCs used in solvent applications, although good practice is to research the country-specific situation in case any previously unidentified applications have arisen. The scope of

8 Emissions of aerosol solvents are included as an aerosol (see Section 7.3).

the search is aided by the fact that the inventory compiler is only looking for applications where ODSs were previously used.

The approach set out in Equation 7.5 can be applied as either a Tier 1a or a Tier 2a method, based as it is on Approach A (emission-factor approach). Whether the approach qualifies as a Tier 1 or Tier 2 method will depend on whether there are identifiable sub-applications within the solvent usages in the reporting country (e.g., the four main areas identified above). As trends have developed towards more controlled solvent environments, the need for a Tier 2 approach has increased. In some cases, there may be highly controlled sub-applications (e.g., in the precision electronics industry) where specific emission factors are fully characterised. These would be treated differently from more general solvent applications which may remain based on the default emission factor. It should be noted that Equation 7.5 assumes total release of solvent within two years regardless of the emission factor applied in year t. Additionally, there is no consideration of recovery and recycling, which may be a factor in some situations. However, it would be assumed that recovery and recycling would, in general, be reflected in reduced sales of virgin materials. Solvent recovered and subsequently destroyed is considered, but is an unlikely course in practice bearing in mind the cost of the chemicals involved.

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