Emission factors 2009 Report 1 A review of methods for determining hot exhaust emission factors for road vehicles

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 reviews the experimental methods used to determine emission factors, and provides recommendations for the future development of the emission factors in the UK. It includes two main elements: (i) an evaluation of the driving cycles used in emission tests and (ii) a review of the parameters recorded during emission tests. A distinction is also made between the improvement of the emission factors in the current database and the requirements with respect to future tests. The Report recommends that more representative driving cycles should be considered for future emission testing, that urban buses and coaches should be treated separately when deriving emission factors, and that when compiling an emission factor database adjustment factors should be applied in order to standardise the data for the gear-shift strategy, the vehicle mileage, the ambient temperature and the ambient humidity. In addition, emission measurements are required for a wider variety of two-wheel vehicles and their operation.