3.2 Non-CO₂ Emissions

The methods (i.e., tiers) for estimating non-CO₂ emissions require different levels of activity and technology detail.

Tier 1. Emissions from all combustion categories are estimated by multiplying the quantity of fuel consumed by an average emission factor. Tier 1 methods do not require detailed activity data.

Tier 2/3. Emissions are estimated by multiplying the quantity of fuel consumed by detailed fuel type and technology-specific emission factors.

Tier 1 methods rely on widely available fuel supply data that assume an average combustion technology is used.

The difference between Tiers 2 and 3 is mainly an increase in the degree of detail in the method. In general, Tier 2 methods use fuel consumption data that are disaggregated according to technology types that are sufficiently homogenous to permit the use of representative emission factors. Tier 3 methods generally estimate emissions according to activity types (km traveled or t-km carried) and specific fuel efficiency or fuel rates or an emission factor or factors expressed directly in terms of a unit of activity.

The general approach to estimate emissions from fuel combustion for each greenhouse gas and sub-source category is Equation 2.3.