Climate and Environmental Protection - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 227

Fig. 15.4 Climate impact of
gases at different altitudes

100

CO 2

HO
2

75

NO X

50

20

0

0 2 4 6 8 10 12 14

altitude [km]

The purpose of optimizing flight routes is to avoid critical atmospheric zones by
changing the altitude or the route of the flight to minimize climate changing
emissions. New turboprop jet engines fly at altitudes between 7,000-8,000 m
(22,951-26,230 ft) and produce the least damage to the environment and the
climate. Despite its economic advantages, the very limited airspace limits the use
of this altitude, especially in Europe and North America [ 22 ].
The altitudes of flight influence fuel consumption and emissions. In flights, the
formation of condensation trails and of cirrus clouds can be avoided by flying at
altitudes in the troposphere. However, at such altitudes the aerodynamics of air-
planes and the efficiency of engines deteriorate due to the denser air, which
increases fuel consumption by about 4% and lengthens flight times. At lower
altitudes the takeoff and the approach time is shortened and the fuel consumption
is decreased in the ascent and in the descent [ 23 ].
The impact of exhaust gas on the climate is different at different altitudes. At
higher altitudes H 2 O and NO x emissions increasingly impact the climate, CO 2
emissions have a decreasing impact; see Fig. 15.4 [ 24 ].
The type of the fuel also determines the climate impact of airplanes. The
comparison of kerosene and hydrogen fuel shows different effects in the atmo-
sphere; see Fig. 15.5 .
Hydrogen significantly reduces negative climate impacts of combustion gases
in comparison to kerosene at all altitudes. However, hydrogen is more a solution
for the long term climate protection due to the technological and economical
difficulties.

15.4.1 Trading with CO 2 Emissions in Aviation

A trip from Europe to the east cost of the USA emits about 674 kg (1,485 lb) of
CO 2 per passenger (between Hamburg and New York). Aviation is responsible for
2.4% of the global CO 2 emissions, but consumption and CO 2 emissions will
increase to 3 or 4% in 2050, in spite of expected improvements in the SFC [ 25 ].
The accelerated introduction of more modern aircraft would reduce emissions
per passenger-kilometer. Other opportunities arise from the optimization of airline