TACKLING AIR POLLUTION FROM LAWNMOWERS TO JUMBO JETS
28 November 1996
Fourteenth session of the Executive Body for the UN/ECE Convention
on Long-range Transboundary Air Pollution (25-28 November 1996)
"The world's current fleet of 400,000 aircraft is responsible for 2 to 3% of our planet's air
pollution. This share may very well double or triple by the year 2015", says Mr. Lars Nordberg
of the United Nations Economic Commission for Europe (UN/ECE). The combustion of aviation
fuels gives off carbon dioxide (CO2), water (H2O) in the form of vapour, and sulphur dioxide
(SO2). It also generates a number of other pollutants, such as carbon monoxide (CO), volatile
organic compounds (VOCs) and particulates. Moreover, the high temperatures in the
combustion chamber lead to the formation of nitrogen oxides (NOx). The Executive Body for
the Convention on Long-range Transboundary Air Pollution addressed this growing problem, at
its fourteenth session from 25 to 28 November 1996.
The Protocols to the UN/ECE Convention on Long-range Transboundary Air Pollution already
recommend specific technologies to control the emissions from traffic, but until now these
recommendations have dealt almost exclusively with road vehicles, such as cars, mopeds, and
lorries.
Now the Executive Body for the Convention is increasingly turning its attention to other sources
of emissions, such as tractors, construction equipment, lawnmowers, ships and aircraft. And
consultations have been held with the International Civil Aviation Organization (ICAO) and the
International Maritime Organization (IMO). This has become necessary because the pollution
that these mobile sources cause is increasingly contributing to acidification, tropospheric ozone
formation and other environmental and health problems.
In the ECE region emissions from off-road vehicles and machines account for 10 to 20% of
total NOx emissions. Diesel-fuelled engines are the biggest culprit. But it is now technically
feasible to cut emissions from diesel engines at reasonable cost. Some of the new technical
options for diesel-fuelled engines are: better combustion chamber design, exhaust-gas
recirculation, electronic engine management and better injection systems. Emissions from off-road vehicles and machines also account for up to 10% of total emissions of volatile organic
compounds (VOCs) in the ECE region. Here, petrol-fuelled two-stroke engines are the biggest
polluters.
Estimates have shown that, for a 500-km journey, the emission of CO2 per passenger-kilometre
(pkm) is the lowest for buses (22 g/pkm) and the highest for planes (146 g/pkm), while high-speed trains and private cars emit 48 g/pkm and 86 g/pkm, respectively. Buses and planes are
the biggest emitters of NOx (479 mg/pkm and 440 mg/pkm); private cars and high-speed trains
emit much less NOx (between 145 and 270 mg/pkm and 87 mg/pkm).[Data transmitted by the
Government of the Netherlands.]
On average, the complete combustion of 1 kg of jet A1 aviation fuel has been estimated to
generate about 3.16 kg of CO2, 1.25 kg of H2O and 1 g of SO2. Estimates of fuel sales to
airlines suggest that this would amount to more than half a billion tons of CO2 and some 2
million tons of NOx emitted each year by aircraft worldwide. 94% of these emissions occur
in the northern hemisphere, mainly in North America (44%) and Europe (30%). Most occur at
an altitude of 9 to 13 km. It has been estimated that 44% of all fuel is consumed above the
tropopause - the limit between the troposphere and the stratosphere. Civil aviation is
responsible for most of this air pollution, but military aviation also plays a significant role. The
impact of light aviation is mainly local.
There are several options for reducing aircraft emissions. There are technical options, such as
measures to improve the engines; operational options, which concern the method of operating
the craft; and economic instruments, i.e. green taxes or other charges that encourage a more
environmentally friendly attitude. To cut emissions the Executive Body of the Convention on
Long-range Transboundary Air Pollution is proposing measures to make engines less polluting.
However, as engines have a long lifetime (almost 30 years for aircraft engines), new technology
penetrates slowly. So it is important to try and upgrade or "retrofit" old engines, as well as to
make new ones cleaner.
To this end, the Executive Body has decided to amend some technical annexes to its NOx and
VOC Protocols. These will in future recommend specific technical solutions to reduce emissions
from mobile sources such as off-road vehicles, ships and aircraft and give an idea of their cost.
"The amendments to the NOx Protocol will come into effect in a month's time; the amendment
to the VOC Protocol cannot come into force until the Protocol itself has been ratified by 16
Signatories", confirms Mr. L. Nordberg.