Air Quality Guidelines Global Update 2005 - World Health ...

SOURCES OF AIR POLLUTION
the above examples, the emission factor for nitrogen oxides from domestic gas
consumption would be expressed as grams of nitrogen oxides per cubic metre of
gas consumed. In the case of cement manufacture, it would be as grams of PM
per tonne of cement produced. Such emission factors are widely published by
national and international agencies and are often specific to particular processes
and applied technologies, including abatement. Thus emissions per tonne of cement
manufactured would be different for a dry than for a wet manufacturing
process, and different for an electrostatic precipitator than for a baghouse filter.
In the case of road vehicles, the vehicle fleet will need to be subdivided according
to the type of vehicle, the fuel it uses, and its age or any abatement technology
fitted. Emission factors are developed specifically for each of these elements.
In conducting calculations for an inventory, it will be necessary not only
to know the type of vehicle in each category but also the annual mileage of that
type of vehicle or the proportion of the total mileage that it represents on a given
road link. Inventories are becoming increasingly sophisticated in disaggregating
vehicles according to their age and mileage, and also in allowing for high-emission
vehicles with faulty abatement devices. It is not feasible to take data directly
from type approval testing and assume that a vehicle that has been operating for,
say, 100 000 km produces the same emissions as a new vehicle on a dynamometer
test. Test cycles, although aiming to reflect the real world, do not always do
so very well.
In compiling emissions inventories it is usual first to define a domain or spatial
resolution, and second to define categories of activity into which emissions will
be subdivided. The largest domain for most emissions inventories is the nation
state, with many countries actively maintaining their own inventories of national
emissions. Such data are valuable in setting targets for reducing emissions and
in monitoring compliance with the requirements of international protocols such
as the EU’s National Emissions Ceilings Directive. International organizations
and programmes such as the European Environment Agency and the European
Monitoring and Evaluation Programme (EMEP) also maintain emissions inventories,
in this case resolved into 50 × 50-km grid squares both at national and international
levels. Many national inventories are more highly resolved; the United
Kingdom initially developed urban inventories on a 1 × 1-km scale, but now has
inventories at this resolution for many pollutants over the entire country.
There are different conventions for subdividing emissions, according to the
activity responsible for them. One example is the SNAP 97 activity system used
within the CORINAIR database by the European Environment Agency. The main
categories used in the SNAP 97 system are listed in Box 1. Within these are numerous
subcategories allowing the inventory user to investigate in greater depth
the relative importance of different source types. Such inventories have many
uses and are critical to the operation of global, regional and mesoscale (1–100
km) air quality models that require spatially disaggregated source input data.
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