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for urban and industrial applications
Mobile sources of emissions: air 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.
Aviaton activities can be grouped into:
Aircraft operations are usually divided into two main parts:
- Category 1 - Civil instrument flight rule (IFR) flights; this includes the majority of commercial air transport;
- Category 2 - Civil visual flight rule (VFR) flights, general aviation; contains small aircraft used for leisure, agriculture, taxi flights, etc.
- Category 3 - Civil helicopters;
- Category 4 - Operational military flights.
In general there are two types of engines: reciprocating piston engines and gas
- The Landing/Take-off (LTO) cycle which includes all activities near the
airport that take place below the altitude of 3000 feet (1000 m).
- Cruise which here is defined as all activities that take place at altitudes
above 3000 feet (1000 m).
The emissions produced by aviation come from the use of jet fuel (jet kerosene
and jet gasoline) and aviation gasoline (used to fuel small piston engine
aircraft only) that are used as fuel for the aircraft. Consequently, the
principal pollutants are those common to other combustion activities, i.e. CO2,
CO, hydrocarbons and oxides of nitrogen, with SO2 emissions being dependent of
the level of sulphur in the fuel. Other important species, emitted at
relatively low concentrations include PM, N2O and CH4.
Tier 1 approach is based on an aggregate figure of fuel consumption for
aviation to be multiplied with average emission factors. The emission factors have been
averaged over all flying phases based on an assumption that 10 percent of the
fuel is used in the LTO (Landing and Take-Off cycle) phase of the flight. There
is currently little information available to estimate emissions from start up
of engines and taxiing and these are not included in the LTO cycle.
In the Tier 2 approach a distinction is made between emissions below and above 1000
m (3000 feet). The emissions in these two flying phases are estimated
separately. Emissions and fuel used in the LTO phase are estimated from
statistics on the number of LTOs and default emission factors or fuel use
factors per LTO.
Relevant European legislation can be found in:
Starting from 1 January 2012 all aircraft operators, performing flights
arriving at or departing from any airport in the territory of the EU will be
included in EU's Emissions Trading System.
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