Background
The final result is given in CO2 equivalent (CO2e) which is the complete mix of different gaseous pollutants coming out of the combustion of fuel in the engine, for which additional conversion factors should be considered.
The CO2e emissions calculation considers:
1/10 Each part (leg) of the trip. For example: From the warehouse of shipper to the port of origin (road - truck), then from the port of origin to the port of destination (sea - vessel), then from the port of destination to the city of destination (rail - train), then from the Railway terminal to the warehouse of consignee (road - truck).
2/10 Load factor for each leg. For example, In the road transit, if the container is a 40', then it is only one container per truck, but if the container is a 20' then, 2 containers may be loaded in a single truck. In this case, the emissions of the truck should be allocated as per load factor. This is 50% of the emissions go to one container and the other 50% to the other
The same happens in the vessel and the rail, where the total emissions should be allocated to the containers on board. This allocation can be done in a simple manner using the capacity used (for example in a vessel carrying 100 containers, the emissions are divided by 100). Another way of allocating (more complex) is based on the actual mass of the container. Then a lighter container will require less energy (fuel) for moving. This way of calculation is more accurate but requires precise data.
3/10 Distance travelled in each leg
4/10 Conditions during the transit. For example, if the truck has to go up the hill, the speed will decrease, but the amount of emissions will increase. The same if a vessel is encountering bad weather or adverse sea conditions, the vessel's engine will need to work harder to keep the vessel moving, reducing average speed but increasing emissions.
5/10 Traveling speed. If the transit conditions are good, the higher the speed, the more emissions.
6/10 Type of vehicle utilized in each leg. For example, if we use a 10,000 TEU vessel for moving 100 containers the emissions will not be the same as if we use a 1,000 TEU vessel for moving the same 100 containers. For inland transport, the emissions attributable to a container are much less for railway than for trucking.
7/10 Vehicle size (mass). The emissions are not only related to the container or its mass, but also the energy required to move the vehicle empty. The size of the vehicle must also be considered. A relatively small vessel with a capacity of 1000 TEU, will produce considerably different emissions when compared to a larger vessel with a capacity of 10,000 TEU. The same applies for trucks and trains.
8/10 Amount of fuel utilized in each leg
9/10 Type of fuel. There are “cleaner” and “dirtier” fuels. For example, a vessel sailing using fuel oil will emit much more CO2e than the same vessel steaming using diesel oil.
10/10 Exhaust emission control device. If the vehicle has installed, for example a catalytic converter, a scrubber or any other exhaust emission control device that may change the composition of the exhaust gasses being vented to the atmosphere.
Current calculation methods are statistically based. So far, no direct measurement is done at the exhaust of the vessels or other vehicles for a particular CO2 calculation. The emissions are estimated based on statistics:
- Vehicle average fuel consumption
- Known / theoretical emissions for the type of vehicle / engine
- CO2 content per kg of fuel
- CO2 emissions per litre or kg of fuel per km
- CO2 emissions per unit of energy contained in the fuel.