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E-1A3b - Road Transportation

This category can be further broken down for reporting purposes into emissions from:

  • 1A3b.i - Cars
    • 1A3b.i1 - Passenger cars with 3-way catalysts
    • 1A3b.i2 - Passenger cars without 3-way catalysts
  • 1A3b.ii - Light duty trucks
    • 1A3b.ii1 - Light duty trucks with 3-way catalysts
    • 1A3b.ii2 - Light duty trucks without 3-way catalysts
  • 1A3b.iii - Heavy duty trucks and buses
  • 1A3b.iv - Motorcycles (including mopeds, scooters, and three-wheelers)
  • 1A3b.v - Evaporative emissions from vehicles
  • 1A3bv.i - Urea-based catalysts

Emissions

Emissions for road transportation are defined by the IPCC in section 3.2 of Volume 2 of (Eggleston H.S. et al. 2006)1.

Emission reporting for road transport can be further broken down into:

  • \(\ce{CO2}\) emissions (from combustion)
  • \(\ce{CO2}\) emissions from urea-based catalysts
  • \(\ce{CH4}\) and \(\ce{N2O}\) emissions

They can be estimated from either:

  • Fuel consumption (tiers 1 and 2); or
  • Vehicle kilometers travelled (tier 3)

\(\ce{CO2}\) emissions

Tier 1

Emissions are calculated per fuel type (\(a\)) based on the parameter \(Fuel_a\) = quantity of fuel sold, measured in \(TJ\).

\[Emission = \sum_{a}[Fuel_a * EF_a] \]

Where:

\[ \begin{array}{rll} Emission &=& \text{Emissions of} \; CO_2 \; &\; (kg) \\ Fuel_a &=& \text{fuel sold} &\; (TJ) \\ EF_a &=& \text{emission factor} &\; (kg/TJ) \\ a &=& \text{type of fuel} \end{array} \]

Emission factors calculated as the carbon content of the fuel multiplied by \(44/12\) and are summarised in table 3.2.1 of (Eggleston H.S. et al. 2006)1:

Fuel Type \(\ce{CO2}\) Emission Factors \((kg/TJ)\)
Motor Gasoline 69 300
Gas / Diesel Oil 74 100
Liquefied Petroleum Gases 63 100
Kerosene 71 900
Lubricants 73 300
Compressed Natural Gas 56 100
Liquefied Natural Gas 56 100

Tier 2

Tier 2 calculations use the same equation as for tier 1, however country-specific carbon content per fuel type are used to determine emission factors, instead of relying on the global average values as used in tier 1.

Tier 3

The IPCC does not provide a tier 3 approach for estimating emissions of \(\ce{CO2}\) for road transport. This is because, for reporting purposes, it is difficult to improve on the tier 2 equations that use direct fuel consumption data.

A tier 3 approach of estimating emissions from Vehicle Kilometers Travelled (VKT) would be less accurate than the tier 1 and 2 approaches. However, when considering mitigation methods, then estimating VKT may be considered an improvement over tier 1 and 2.

\(\ce{CO2}\) emissions from urea-based catalysts

Emissions from the use of urea-based additives are not described with the tier approach, the IPCC present only the following consumption based equation:

\[Emission = Activity \cdot \frac{12}{60} \cdot Purity \cdot \frac{44}{12} \]

Where:

\[ \begin{array}{rll} Emission &=& \text{emissions of} \; \ce{CO2} &\; (kg) \\ Activity &=& \text{amount of additive consumed} &\; (Gg) \\ Purity &=& \text{perctantage purity of additive} &\; \\ \end{array} \]

\(\ce{CH4}\) and \(\ce{N2O}\) emissions

\(\ce{CH4}\) and \(\ce{N2O}\) emissions are harder to estimate and depend largely on factors such as the distribution of emission control technology in the fleet. For this reason, tier 2 and 3 methods address variations in the fleet as well as driving conditions.

Note: while \(\ce{CO2}\) emissions from biofuels are not required by the IPCC for reporting national totals (as they are biogenic), \(\ce{CH4}\) and \(\ce{N2O}\) emissions from biofuels are considered anthropogenic and should be reported.

Tier 1

This approach follows the tier 1 approach for \(\ce{CO2}\) emissions and is base on fuel consumption data, broken down by fuel type:

\[Emission = \sum_{a}[Fuel_a * EF_a] \]

Where:

\[ \begin{array}{rll} Emission &=& \text{emissions} &\; (kg) \\ Fuel_a &=& \text{fuel sold} &\; (TJ) \\ EF_a &=& \text{emission factor} &\; (kg/TJ) \\ a &=& \text{type of fuel} &\; \end{array} \]

Tier 2

Tier 2 further breaks down fuel consumption by vehicle type and emission control technology:

\[Emission = \sum_{a,b,c}[Fuel_{a,b,c} * EF_{a,b,c}] \]

Where:

\[ \begin{array}{rll} Emission &=& \text{emissions} &\; (kg) \\ Fuel_a &=& \text{fuel sold} &\; (TJ) \\ EF_a &=& \text{emission factor} &\; (kg/TJ) \\ a &=& \text{type of fuel}\\ b &=& \text{type of vehicle}\\ c &=& \text{type of emission control technology} \end{array} \]

Tier 3

Tier 3 improves on the lower tiers by using Vehicle Kilometers Travelled, as well as roughly accounting for the cold-start phase:

\[Emission = \sum_{a,b,c,d}[Distance_{a,b,c,d} \cdot EF_{a,b,c,d}] + \sum_{a,b,c,d}C\]

Where:

\[ \begin{array}{rll} Emission &=& \text{emissions} &\; (kg) \\ Distance_{a,b,c,d} &=& \text{distance travelled (VKT)} &\; (km) \\ EF_{a,b,c,d} &=& \text{emission factor} &\; (kg/km) \\ C_{a,b,c,d} &=& \text{cold start emissions} &\; (kg) \\ a &=& \text{type of fuel}\\ b &=& \text{type of vehicle}\\ c &=& \text{type of emission control technology}\\ d &=& \text{type of operating conditions} \end{array} \]

The cold-start phase is roughly estimated to the first 3km travelled per journey and takes into account the fact that catalysts only start to operate when engine temperatures reach 300 C.

Mitigation

For mitigation strategies see M-1A - Land-based Transport.

  1. Eggleston H.S., Buendia L., Miwa K., Ngara T., and Tanabe K. 2006. “2006 IPCC Guidelines for National Greenhouse Gas Inventories.” IGES, Japan. https://www.ipcc-nggip.iges.or.jp/public/2006gl/index.html. ↩↩