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 summarises the work conducted on the project. The Report covers three different types of source: hot exhaust emissions, cold-start emissions and evaporative emissions, with most of the work focussing on hot exhaust emissions. Aspects of hot exhaust emissions which are covered include driving cycles and test parameters, modelling approaches, the effects of fuel properties, the development of emission factors for UK vehicles, and the development of new scaling factors to take account of the effects of emission degradation and changes to fuels. For cold-start emissions the main conclusion is that the current NAEI model ought to be updated to reflect the COPERT 4 methodology. However, other new cold-start models ought to be available in 2009, and when these are published they should be considered for inclusion in the NAEI. The main conclusion of the work on evaporative emissions was that, given that considerable effort has be put into developing the new method in COPERT 4 and the flexibility it offers, there would be sufficient justification for changing the NAEI to include this method.

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