TRL was commissioned by the Department for Transport to review the approach used in the National Atmospheric Emissions Inventory (NAEI) for estimating emissions from road vehicles, and to propose new methodologies. This Report describes the development of new exhaust emission factors. Emission data for light-duty vehicles (LDVs) and heavy-duty vehicles (HDVs) from various European test programmes were collected. The methods used for determining emission factors are described in detail. Separate databases were compiled for LDVs and HDVs, and in each case for regulated and unregulated pollutants. For LDVs, the emission factors for regulated pollutants were developed from the relevant databases for vehicles complying with pre-Euro 1 to Euro 6 emission standards. For HDVs, the emission factors for regulated pollutants were not calculated from the corresponding database; in order to provide greater flexibility they were based upon the average-speed functions from the European ARTEMIS project. The emission factors for HDVs covered the pre-Euro I to Euro VI emission standards. For petrol and diesel cars the CO2 emission functions were derived from the type approval data for new cars. The emission factors for mopeds were taken from the COPERT 4 model, and those for motorcycles were taken from ARTEMIS. The unregulated pollutants considered were methane, 1,3-butadiene, benzene, nitrous oxide, ammonia, polycyclic aromatic hydrocarbons, nitrogen dioxide and particle size fractions. The emission factors for these pollutants were based upon a combination of the relevant databases and the literature.

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