Introduction

A new database of vehicle emission factors for NOx, PM10, CO, HC (VOCs, including methane), benzene, 1,3-butadiene, CO2 and fuel consumption has been prepared from a review and assessment of the new set of speed-emission coefficients reported by TRL from their analysis of new emission test results on vehicles meeting mainly Euro I and II standards. Details of the vehicles tested and the results obtained are provided in the TRL Report by Barlow, Hickman and Boulter which went out for consultation in October 2001.

This spreadsheet provides the complete set of speed-emission factor coefficients for NOx, PM10, CO, HC, benzene, 1,3-butadiene, CO2 and fuel consumption in its most disaggregated form. Coefficients are provided for functions relating emission factor in grammes per kilometre to average speed, for all the different types and sizes of vehicles in the UK fleet, in all the categories of European emission standards from pre-Euro I (<1993) right through to Euro IV (2005). Modellers may require these raw speed-emission coefficients for all the many individual categories of vehicles for use with their own information on the age composition (proportion by Euro standard) within the fleet mix for the area they are covering. Emission factors for CO2 refer to 'ultimate CO2', referring to all the carbon in the fuel emitted at the tailpipe as CO2, CO, unburned hydrocarbons and particulate matter which ultimately have the potential in forming CO2. Units of emission factors calculated from these coefficients are given as both g CO2/km and as g C/km.

The spreadsheet shows in a column to the right of the tables of coefficients an example of how the coefficients are used in the equation to calculate an emission factor at an average speed of 40 kph. The emission coefficients themselves are locked to prevent accidental changes, but the speeds may be altered to derive the emission factors from the equations.

Other users may require more aggregated factors for the main types of vehicles (e.g. car, van, HGV), weighted by the composition of the national fleet in different years. Fleet-weighted emission factors derived from these coefficients for average speeds on urban, rural and highway roads are also available on the NAEI Emission Factor Database, but at the moment only the fleet-weighted factors for NOx and PM10 are based on these new speed-emission coefficients. Fleet-weighted factors for CO, NMVOCs, benzene, 1,3-butadiene and CO2 based on the new speed-emission coefficients will be included shortly. The fleet-weighted factors are in the form previously available on the RSK website, but supplied by the NAEI, and are weighted by the composition of the national vehicle fleet, as forecast by the NAEI road transport fleet projections taking account of the base assumptions in fleet turnover predicted by DfT. The UK fleet composition data used for this are available on this website. Further details on the base assumptions were given in the Technical Annexe Section 1 (A51-A56) of the consultation document of the Air Quality Strategy for England, Scotland, Wales and Northern Ireland published in September 2001 by DEFRA in partnership with the Scottish Executive, the National Assembly for Wales and the Department of the Environment for Northern Ireland.

The new database of emission factors and the same default NAEI fleet projections (by Euro standard) are the basis of the emission factor spreadsheet modelling tool available from Stanger Science & Environment through the Air Quality Modelling Helpdesk. Local Authorities are advised to use this modelling tool to calculate an overall NOx and PM10 emission factor from their own fleet mix for a traffic flow.

Basis of the New Emission Factors

The new database was prepared by NETCEN working in the National Atmospheric Emissions Inventory Programme in consultation with TRL. The finalised set of emission factors is based on:

· Existing factors used up until now in the NAEI for pre-Euro I vehicles, provided by TRL in 1998. Some modifications were made following further consideration of a) the speed dependence of factors for pre-1988 HGVs and buses; b) the factors for pre-Euro I LGVs; c) the speed-dependence of PM10 emissions from petrol vehicles.

· Adoption of the new TRL factors for Euro I and II vehicles. Previously, with exception of some Euro I factors for petrol cars available from TRL in 1998, these had been based on estimates from the European MEET and COPERT group of experts. The use of estimates for Euro I and II vehicles was necessary because no, or very few, measurements of emissions from in-service vehicles of these classes had been made.

· A reconsideration of the reduction in emissions anticipated for Euro III and IV vehicles, in light of what the new factors for Euro II vehicles suggest vehicle and engine manufacturers will have to achieve in order to meet the emission limits for these classes of vehicles.

Justification for adopting these emission factors and the various assumptions made for Euro III and IV vehicles will be given in a later report.

Use of the New Emission Factors

These emission factors are now being used in the NAEI, although emissions calculated for the 2000 version of the NAEI before these factors were finalised are still based on the old emission factors.

This database of emission factors has been incorporated into the 2002 version of the Stanger Emission Factor Toolkit. available through the Modelling Helpdesk, available at http://www.stanger.co.uk/JointProjects/DEFRA-Home.asp?jointprojectid=7

Using these coefficients, the NAEI has generate a revised set of fleet-weighted road-type emission factors for NOx and PM10 on the new Emission Factor Database on this NAEI website, replacing the old RSK EFDb factors. These are weighted by the proportion of kilometres travelled by each Euro standard in the national fleet. Factors for other pollutants are also available there, but the factors for CO, NMVOCs, benzene, 1,3-butadiene and CO2 are not yet updated with these revised set of speed-emission equations. This will be undertaken shortly.

The fleet composition data are available on the same page of this website. These data also include a set of emission scaling factors for each pollutant, reflecting improvements in the quality of fuel since the emission factors were measured and some degree of retrofitting and technology conversions in the national fleet. The emission factors calculated by these speed-emission equations should be multiplied by the appropriate scaling factor for the year in question and then combined with the fleet composition data to derive ultimate emission factors for a particular traffic mix.

Illustrative examples of factors for each Euro standard within each group of vehicle types aggregated by vehicle size are shown in this spreadsheet. Factors are shown for typical speeds for each class of vehicle on urban, rural and highway roads.

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