Methoden voor de berekening van de emissies door mobiele ... - CBS

classification due to the large sample size. After 2000 the specific consumption figures have been
extrapolated based on expert judgement.
The fuel consumption per road type is calculated from the average consumption by using model
calculations for the variations in fuel consumption between travelling on various road types, and is
therefore more uncertain than the average consumption.
The fuel consumption by road vehicles concerns calculated figures (resulting from specific fuel
consumption and vehicle kilometres) and is more uncertain than both elements separately.
Fuel sales to road traffic are determined based on a survey among fuel suppliers (oil companies) and
is relatively accurate (A). These figures are used to calculate the IPCC-emissions.
1.9.2 Uncertainties in emission factors (Appendix 1B)
Regarding the uncertainty in the emission factors of road vehicles, a distinction can be made
according to 1) fuel-related emission factors, 2) regulated combustion and emission factors 3) nonregulated
combustion and emission factors, 4) evaporative emission factors and 5) wear emission
factors.
Note to 1: Fuel-related emission factors are used when calculating CO2, SO2 and heavy metals. These
emissions are calculated by multiplying the fuel consumption with fuel-related emission factors
(grams/kg of fuel). Of these emission factors, CO2 is the most certain because this depends only on
the carbon content of the fuel, and this carbon content is relatively certain. SO2 depends on the
sulphur content, and since in recent years this has not been structurally measured, the sulphur
content, especially of petrol, is very uncertain. Although the emission factors for heavy metals are
based on a recent study, they are still uncertain because the content of heavy metals depends on the
composition of the refined crude oil and the fuel additives. Both can vary strongly.
Note to 2: Regulated combustion and emission factors are used for CO, VOC, NOx and in the case of
diesel vehicles, for PM10 as well. Road vehicles have been subjected to emission norms for more than
a decade; consequently, a relatively large number of measurement results are available. One example
is the annual in-use compliance programme of the TNO, during which several dozen of vehicles are
measured per year. The reliability of these emission factors is increased since using VERSIT+, but
uncertainties still exist regarding the correction factors for the cold start, ageing and the use of air
conditioners.
Note to 3: Non-regulated combustion emission factors are used among other things for N2O and VOC
components such as aromatics (including benzene) and PAHs. Because the profiles are from the mid-
1980s and both the fuel composition and the engine technology have changed since then, the
reliability of these profiles has declined sharply. In 2002, as expected, a large-scale measurement
programme was conducted to update the VOC profiles. The N2O emission factors of passenger cars
have recently been ascertained as part of a comprehensive measurement study and are therefore
relatively reliable (B).
Note to 4: Evaporative emission factors express the quantity of evaporated petrol per vehicle per day.
This depends on the age of the vehicle, because new vehicles must comply to stricter demands for the
maximum evaporative emissions than older vehicles. Moreover, the evaporative emission depends on
vehicle usage, because many short trips lead to more evaporative emissions than fewer long trips. In
addition, the outdoor temperature is important. The evaporative emissions of road vehicles are
scarcely measured in the Netherlands, and emission factors are therefore based on the emission
norms and the measurement results in other European countries.
Note to 5: Wear emission factors are derived from a mass balance and assumptions about the content
of particulate matter in the total wear mass. This assumption is very uncertain. The zinc content of
tyres, which was modified by the traffic task group, has been recently confirmed in research conducted
by BLIC, a central organization of tyre manufacturers.
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