levels (national socioeconomic statistics, for example) to allow indirect
calculations/estimations of the emission sources (Ponche 2002). Two main types of
approaches are again distinguished:
• The top-down approach: used when, for a given area, there is lack of detailed
data and to obtain the required emission resolution (scale) it is necessary to
disaggregate the emissions calculated for a larger area. This approach computes
the total amount of aggregated emission using for example data like total fuel
consumption for the whole city or the whole country during a full year. This
total is then distributed in time and space using the distribution of parameters
linked with the activity responsible of the emissions (like population, road
network, etc.).
• The bottom-up approach: used when for a given area numerous data at small
scales can be collected and must be aggregated to higher sales. In the bottom-up
approach, the emissions are directly computed from activity values in time and
space.
The level of aggregation of the input data needed to apply these two types of
methods is different. Usually, the bottom-up approach is preferred and also recommended to develop spatialized emission inventories (SEIs) and can reduce
uncertainties. Nevertheless, the top-down approach is also generally used to control
and correct the emission estimates. Applications show that in most cases the
top-down and bottom-up approaches do not give the same results.
In order to harmonize European emission inventories, EMEP/EEA (2009a, b)
proposed a guidebook with basic principles on how to construct an emissions
inventory, the specific estimation methods and emission factors. In this guidebook,
one key issue is the classification of the emission sources.
Classification of Emission Sources
The emission sources are usually at first classified in two classes depending on the
emission process: natural sources and anthropogenic sources. They are also classified in three categories depending on their geographic characteristics, location and
type:
– point sources, that are precisely located and often concern industrial sites, where
large amount of atmospheric pollutant are emitted from very a small area
(compared to the space resolution of the emission inventory);
– line sources, that correspond to main transportation infrastructures. If the traffic
(road, air, railway, ship) on these routes is dense enough (relatively to the time
and space resolutions of the emission inventory), they can be considered as
continuous emission lines;
– area sources, that include all other sources as residential areas, industrial areas,
etc., where numerous small emitters are spread/diffused.
In order to categorize the anthropogenic sources, several classifications in terms
of activity, sectors and fuel use were proposed. At European level, SNAP97
(Selected Nomenclature for Air Pollution) is a reference classification proposed by
2 A Framework for Integrated Assessment Modelling
21
calculations/estimations of the emission sources (Ponche 2002). Two main types of
approaches are again distinguished:
• The top-down approach: used when, for a given area, there is lack of detailed
data and to obtain the required emission resolution (scale) it is necessary to
disaggregate the emissions calculated for a larger area. This approach computes
the total amount of aggregated emission using for example data like total fuel
consumption for the whole city or the whole country during a full year. This
total is then distributed in time and space using the distribution of parameters
linked with the activity responsible of the emissions (like population, road
network, etc.).
• The bottom-up approach: used when for a given area numerous data at small
scales can be collected and must be aggregated to higher sales. In the bottom-up
approach, the emissions are directly computed from activity values in time and
space.
The level of aggregation of the input data needed to apply these two types of
methods is different. Usually, the bottom-up approach is preferred and also recommended to develop spatialized emission inventories (SEIs) and can reduce
uncertainties. Nevertheless, the top-down approach is also generally used to control
and correct the emission estimates. Applications show that in most cases the
top-down and bottom-up approaches do not give the same results.
In order to harmonize European emission inventories, EMEP/EEA (2009a, b)
proposed a guidebook with basic principles on how to construct an emissions
inventory, the specific estimation methods and emission factors. In this guidebook,
one key issue is the classification of the emission sources.
Classification of Emission Sources
The emission sources are usually at first classified in two classes depending on the
emission process: natural sources and anthropogenic sources. They are also classified in three categories depending on their geographic characteristics, location and
type:
– point sources, that are precisely located and often concern industrial sites, where
large amount of atmospheric pollutant are emitted from very a small area
(compared to the space resolution of the emission inventory);
– line sources, that correspond to main transportation infrastructures. If the traffic
(road, air, railway, ship) on these routes is dense enough (relatively to the time
and space resolutions of the emission inventory), they can be considered as
continuous emission lines;
– area sources, that include all other sources as residential areas, industrial areas,
etc., where numerous small emitters are spread/diffused.
In order to categorize the anthropogenic sources, several classifications in terms
of activity, sectors and fuel use were proposed. At European level, SNAP97
(Selected Nomenclature for Air Pollution) is a reference classification proposed by
2 A Framework for Integrated Assessment Modelling
21