air quality management information system |
for urban and industrial applications
Mobile sources of emissions: rail transport
While the traditional image of air pollution is still associated with a large industrial stack belching black smoke,
the majority of urban air pollution comes from: transport, that is mobile emission sources.
Cars and their internal combustion engines, but also trains, ships and aircraft all burn considerable amounts of fuel
and do contribute significantly to air pollution both locally but also on a global scale.
Some of the complexities of addressing the transportation system include:
- Highly dynamic nature of these emissions: the sources move, even though along well defined paths;
- The transient nature: these movements usually exhibit well defined patterns in time
(the urban rush hour being an obvious example) with the resulting short-term maxima,
usually underestimated with any long-term average representation;
- A strong psychological element attached to individual freedom of movement (and private cars) that
makes any limitations for individual passenger cars usually rather controversial.
Diesel engines are the predominant form of power unit within the railways industry,
in particular for the long haul, over large distances where electrification would be costly.
The engines can be fitted into three distinct types of propulsion units:
- Shunting locomotives: equipped with diesel engines whose power output is
typically in the range 200 to 2 000 kW;
- Railcars: mainly used for short distance rail traction, e.g. urban/suburban traffic.
They are equipped with diesel engines having a power output of about 150 to 1 000 kW;
Line haul locomotives: used for long distance rail traction both for freight and
passengers. They are equipped with diesel engines having a power output of
around 400 to 4,000 kW
Typical fuel consumption for locomotives would be in the order of hundred to
250 kilo of fuel oil per hour, translating into emission values of 1-4 g NOx/s.
There are, of course fully electric locomotive and trains, taking their
power from an overhead wire, sometimes a third rail. They do not generate local,
mobile emissions, but contribute to the load of whatever power generating system
(thermoelectric based on coal, oil, or gas; nuclear; hydro, any other renewable)
feeds their grid. Light trains in urban areas will usually be electrified,
as are streetcar and subway systems as a major component of urban public transport.
| print page