The previous sections have defined the fuels and source categories used in the NAEI. The aim of this section is to describe in detail the methodology used to estimate the emissions for each source category.

It would be impossible to measure every emission source in the UK directly; therefore, the majority of emissions are estimated from other information such as fuel consumption, distance travelled or some other statistical data related to the emissions. Estimates are calculated by applying an emission factor to an appropriate statistic. That is:

Emission = Factor × Statistic

The emission factors have been derived from measurements on a number of installations representative of the source and the resulting factor is assumed to apply to all installations in that source.

For certain sectors, emission data are available for individual sites from databases such as the Environment Agency’s Pollution Inventory (PI). Hence the emission for a particular sector can be calculated as the sum of the emissions from these point sources. That is:

Emission = S Point Source Emissions

However it is necessary to make an estimate of the fuel consumption associated with these point sources, so that the emissions from non-point sources can be estimated from fuel consumption data without double counting.

Section 2.2 discusses the base combustion module which corresponds to the more straight forward combustion emissions. Subsequent sections discuss the other modules which are based on more complex models or require further explanation.