The Intergovernmental Panel on Climate Change (IPCC) road default for diesel methane and nitrous oxide assumes 5 km per litre. Does that matter for an Indian truck doing 3.5?

Barely. IPCC 2006 Table 3.2.2 gives diesel 3.9 kilograms each of methane and nitrous oxide per terajoule, from a European heavy truck at an assumed 5 km per litre. Those gases are only about 1.5 percent of the carbon dioxide (CO2), so even a large error moves the total by well under 1.5 percent.

Where the default comes from

Table 3.2.2 gives gas or diesel oil a default of 3.9 kilograms of methane (CH4) per terajoule, range 1.6 to 9.5, and 3.9 of nitrous oxide (N2O), range 1.3 to 12. Note (e) says the value is based on a European heavy duty diesel truck. Note (a) says the per-terajoule values were derived with assumed fuel consumption of 5 km per litre for diesel vehicles.

What the guide tells you to do

It says CH4 and N2O depend largely on combustion and emission control technology, so default fuel-based factors that do not specify vehicle technology are highly uncertain. If actual representative fuel economy values are available, it recommends using them with total fuel use to estimate distance travelled, and encourages higher-tier factors. The chapter does print per-kilometre figures in Table 3.2.3, from United States data: for a heavy duty diesel vehicle, all technologies, running emissions of 3 milligrams of N2O and 4 milligrams of CH4 per kilometre (cold start adds -2 and -11 milligrams per start), and 1 milligram of each per kilometre for a light duty diesel vehicle. But its per-terajoule default in Table 3.2.2 is the one meant for fuel-based use, and the two differ.

How big can the 5 against 3.5 gap be

Our arithmetic. If the same grams per kilometre held for a truck at 3.5 km per litre, it burns more fuel per kilometre, so the grams per terajoule would be 3.5 / 5 = 0.7 of the default, 30 percent lower. If instead CH4 and N2O rose with the fuel burnt, the default per terajoule would stand. We cannot tell which is closer for an Indian truck. The guide's own diesel range is wide, 1.6 to 9.5 kilograms of CH4 and 1.3 to 12 of N2O per terajoule, and the Table 3.2.3 heavy duty figures (4 milligrams of CH4 and 3 of N2O per kilometre) at 3.5 km per litre work out, by our arithmetic, to roughly 0.4 kilograms of CH4 and 0.3 of N2O per terajoule, about ten times below 3.9. So the 0.7 is one worked case, not a limit.

Size matters. The methane page here puts CH4 and N2O for road diesel at about 1.5 percent of the CO2. That share is small enough that the safe conclusion does not need the 0.7: CH4 plus N2O are about 1.5 percent of the CO2, so even a large error in the default moves the total by well under 1.5 percent.

Same split in the Greenhouse Gas (GHG) Protocol's Scope 3 guide

Its Category 4 guide says its transport calculation tool combines the fuel-based and distance-based methods because CO2 is better estimated from fuel use, and CH4 and N2O are better estimated from distance travelled. It also says the tool was built for Scope 1, so for Scope 3 you should put in life cycle factors. The IPCC chapter is more cautious: it says distance data and fuel split by type may be considerably less certain than overall fuel sold.

What to do

• Keep litres and kilometres per truck. The litres give CO2, the kilometres are the base for any per-kilometre factor you later get from a vehicle maker or a study.
• Use the 3.9 and 3.9 defaults if you want CH4 and N2O, say they are IPCC 2006 defaults, and name the 5 km per litre assumption in your notes.
• If a buyer asks for CO2 only, say so and say the CH4 and N2O share is about 1.5 percent.

One truck, 10,000 km a year at 3.5 km per litre

• Diesel: 10,000 / 3.5 = 2,857 litres
• CO2: 2,857 x 2.645 = 7,557 kilograms
• Energy: 7,557 / 74,100 kilograms per terajoule = 0.102 terajoules
• Default CH4: 0.102 x 3.9 = 0.40 kilograms. Default N2O: 0.102 x 3.9 = 0.40 kilograms
• If the per-kilometre value held instead: 0.40 x 0.7 = 0.28 kilograms each
• Gap: 0.12 kilograms each. In CO2 equivalent (AR5 warming potentials, 28 for CH4 and 265 for N2O): 0.12 x 28 = about 3 kilograms plus 0.12 x 265 = about 32 kilograms, about 35 kilograms, or 0.5 percent of 7,557 kilograms of CO2

Diesel at 2.645 kg CO2 per litre is Senseible's combustion factor; 74,100 kg per terajoule is the IPCC road default. The 3.5 km per litre is an example. Other warming potentials (for example AR6) give a different CO2e figure.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so a truck's diesel litres are in one place. Kilometres come from your own logbook or odometer record. It does not choose between IPCC and vehicle-specific methane factors for you.

• Methane and nitrous oxide from diesel combustion
• Indian truck diesel mileage by size
• Methane from CNG and LNG vehicles per kilometre
• Transport fuel spend to litres

Sources: IPCC 2006 Guidelines, Volume 2, Chapter 3 Mobile Combustion, GHG Protocol Technical Guidance for Calculating Scope 3 Emissions, Category 4 (transport calculation tool)

Last reviewed 2026-11-05. Table values and notes are from IPCC 2006 Volume 2 Chapter 3; the tool description is from the GHG Protocol Category 4 guide. The 0.7 ratio and the per-terajoule conversion of Table 3.2.3 are our arithmetic, and we do not know which side an Indian truck sits.