This Report summarises a research project in which the scientific understanding of ‘instantaneous’ emission models for road vehicles was assessed. Instantaneous emission models aim to provide a precise description of vehicle emission behaviour by relating emission rates to vehicle operation during a series of short time steps (often one second).
The overall aims of this project were to review and evaluate instantaneous emission data and models, and to show how improvements in modelling could lead to improvements in the prediction and control of local air quality. The project was divided into four main Tasks:
• Task 1: A review of existing instantaneous emission models for road vehicles.
• Task 2: A model evaluation and inter-comparison exercise.
• Task 3: An examination of the links between instantaneous emission models, microsimulation traffic models and air pollution models.
• Task 4: Summary and recommendations for model development and future research.

This Report (Task 4) summarises the work conducted on Tasks 1 to 3. The Report concludes that the instantaneous emission models PHEM and MODEM are equally good at predicting estimation from light-duty vehicles over a trip, even though MODEM is older than PHEM, uses assumptions for Euro III and Euro IV vehicles rather than measurements, and includes no adjustment for the distortion of the emission signal during measurement.
A further conclusions was that one of the main challenges in micro-scale model integration is the matching of the different vehicle types defined in the traffic simulation and emissions components. The systems of vehicle classification required for emission models are generally more complex than those used in traffic models. Ideally, the aim would be to link the most detailed and up-to-date instantaneous emission model to the most appropriate traffic model.
The links between instantaneous emissions and air pollution dispersion modelling tools remain largely untested.
The report provides recommendations and a draft specification for the development of a new instantaneous emission model.

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