Choice of method

There are three methodological options for estimating CO2, CH4, and N2O emissions from combustion in off-road mobile sources: Tier 1, Tier 2, and Tier 3. Figure 3.3.1: Decision tree for estimating emissions from off-road vehicles provides the criteria for choosing the appropriate method. The preferred method of determining CO2 emissions is to use fuel consumption for each fuel type on a country-specific basis. However, there may be difficulties with activity data because of the number and diversity of equipment types, locations, and usage

12 Appendix B of this reference provides Source Classification Codes (SCC) and definitions for: (a) Recreational vehicles; (b) Construction equipment; (c) Industrial equipment; (d) Lawn and garden equipment; (e) Agricultural equipment; (f) Commercial equipment; (g) Logging; (h) GSE/underground mining/oil field equipment; (i) Recreational marine and; (j) Railway maintenance are provided in Appendix B.

patterns associated with off-road vehicles and machinery. Furthermore, statistical data on fuel consumption by off-road vehicles are not often collected and published. In this case higher tier methods will be needed for CO2 and they are necessary for non-CO2 gases because these are much more dependent on technology and operating conditions.

A single method is provided for estimating CO2 emissions from catalytic converters using urea. Many types of off-road vehicles will not have catalytic converters installed, but emission controls will probably increasingly be used for some categories of off-road vehicles, especially those operated in urban areas (e.g., airport or harbour ground support equipment) in developed countries. If catalytic converters using urea are used in off-road vehicles, the associated CO2 emissions should be estimated.

The general method for estimating greenhouse gas emissions from energy sources can be described as:

Equation 3.3.1 Tier 1 emissions estimate


Emissions = Emissions (kg)

Fuelj = fuel consumed (as represented by fuel sold) (TJ) EFj = emission factor (kg/TJ)

For Tier 1, emissions are estimated using fuel-specific default emission factors as listed in Table 3.3.1, assuming that for each fuel type, the total fuel is consumed by a single off-road source category.

For Tier 2, emissions are estimated using country-specific and fuel-specific emission factors which, if available, are specific to broad type of vehicle or machinery. There is little or no advantage in going beyond Tier 2 for CO2 emissions estimates, provided reliable fuel consumption data are available.

Equation 3.3.2 Tier 2 emissions estimate


Emissions =emissions (kg)

Fueli,j = fuel consumed (as represented by fuel sold) (TJ)

EFi,j = emission factor (kg/TJ)

i = vehicle/equipment type j = fuel type

For Tier 3, if data are available, the emissions can be estimated from annual hours of use and equipment-specific parameters, such as rated power, load factor, and emission factors based on power usage. For off-road vehicles, these data may not be systematically collected, published, or available in sufficient detail, and may have to be estimated using a combination of data and assumptions.

Figure 3.3.1 Decision tree for estimating emissions from off-road vehicles

Figure 3.3.1 Decision tree for estimating emissions from off-road vehicles

Note: See Volume 1 Chapter 4, "Methodological Choice and Key Categories" (noting section 4.1.2 on limited resources) for discussion of key categories and use of decision trees.

Note: See Volume 1 Chapter 4, "Methodological Choice and Key Categories" (noting section 4.1.2 on limited resources) for discussion of key categories and use of decision trees.

Equation 3.3.3 represents the Tier 3 methodology, where the following basic equation is applied to calculate emissions (in Gg):

Equation 3.3.3 Tier 3 emissions estimate


Emission = emission in kg. NiJ = source population


= annual hours of use of vehicle i (h)


= average rated power of vehicle i (kW)


= typical load factor of vehicle i (fraction between 0 and 1)


= average emission factor for use of fuel j in vehicle i (kg/kWh)


= off-road vehicle type


= fuel type

Equation 3.3.3 may be stratified by factors such as age, technological vintage or usage pattern, and this will increase the accuracy of the estimates provided self-consistent sets of parameters H, P, LF and EF are available to support the stratification, (EEA 2005). Other detailed modelling tools are available for estimating off-road emissions using Tier 3 methodology (e.g., NONROAD (USEPA 2005a) and COPERT (Ntziachristos 2000)).

For estimating CO2 emissions from use of urea-based additives in catalytic converters (non-combustive emissions), Equation 3.3.4 is used:

Equation 3.3.4 Emissions from urea-based catalytic converters

Emissions = Activity • I — I • Purity Factor • I —


Emission = Emission of CO2 (kg)

Activity = Mass (kg) of urea-based additive consumed for use in catalytic converters

Purity factor = Fraction of urea in the urea-based additive (if percent, divide by 100)

The factor (12/60) captures the stochiometric conversion from urea ((CO(NH2)2)) to carbon, while factor (44/12) converts carbon to CO2.

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