Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
Table of contents | Previous page | Next page
1.5. Mitigation
Other reports in this collection
Environmental issues regarding emissions from aircraft were originally related to their contribution to local air quality in the vicinity of airports. These considerations led
to the introduction of legislation in the United States resulting in domestic regulatory standards. Subsequently, ICAO developed international standards and
recommended practices for the control of fuel venting and emissions of carbon moNO x ide, hydrocarbons, nitrogen oxides, and smoke from aircraft engines over a
prescribed landing/take-off (LTO) cycle below 915 m (3,000 feet) (ICAO, 1981). Although the global environmental effects of aircraft emissions have been a matter of
much debate at a scientific and technical level, there are no specific standards for the control of emissions from aircraft during cruise. However, the LTO standards in
place do indirectly limit emissions from an engine during climb and cruise.
The UNFCCC seeks to stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate
system. Its coverage includes emissions from all sources and all sectors, although it does not specifically refer to aviation. However, the Kyoto Protocol to the
Convention, which was agreed in December 1997, includes two elements that are particularly relevant to aviation. First, the Kyoto Protocol requires developed
countries to reduce their total national emissions from all sources by an average of about 5% for the years 2008-2012 compared with 1990 (with differences for
individual countries). It contains a provision for so called "flexible mechanisms"-including emissions trading, "joint implementation," and a "clean development
mechanism." Secondly, the Kyoto Protocol contains a provision (Article 2) that calls on developed countries to pursue policies and measures for the limitation or
reduction of greenhouse gases from "aviation bunker fuels," working through ICAO. These issues are discussed in Chapter 10.
Future mitigation options and strategies will need to consider the motivation for increasing operational efficiencies and reducing fuel use in light of other environmental
effects of aviation, such as noise. The availability and cost of fuel in the overall budget of aircraft operators will continue to exert strong pressure for fuel efficiency. A
number of technological improvements (e.g., to airframe aerodynamics, aircraft weight, and engine cycle performance) over the years have improved the fuel efficiency
of subsonic aircraft and engines. These innovations have had a direct impact on the amount of CO2 and H2O emitted by aircraft (the less fuel consumed, the less CO2 and H2O emitted) and have reduced CO and hydrocarbon emissions. The effect on emissions of NOx and particles is not as simple, however. The drive to improve fuel
efficiency and reduce aircraft noise has resulted in a general trend to higher operating pressures and temperatures in engines and increased production of NO x for a
given type of combustor technology. Combustor design changes can offset this problem to some extent but may result in increased complexity and weight. Different
considerations may apply to the potential second generation of civil supersonic aircraft. The current status and potential changes in the technology of engines and
http://www.ipcc.ch/ipccreports/sres/aviation/018.htm (1 von 2)08.05.2008 02:41:32