Dr. Peter F.J. van Velthoven
Atmospheric effects of aircraft emissions
Fresh contrail affected by aircraft vortices, observed
12 May 2001, 15h55 UT over Bilthoven.
Impacts on atmospheric composition
Present-day commercial jet aircraft have cruise altitudes of 8-13 km.
The emissions from these aircraft change the atmospheric composition:
- Directly: by emitting carbon dioxide (CO2), nitrogen oxides (NOx = NO +
NO2), water vapour, unburnt hydrocarbons, soot, and sulfate particles.
- Indirectly: by a chemical reaction chain similar to smog-formation the
greenhouse gas ozone
(O3) can be formed. In this reaction chain nitrogen oxides act as a catalyst
under the influence of sunlight. The formed ozone has a lifetime of several weeks up to months in the troposphere.
As a result of these chemical reations also
the concentration of methane (CH4), another greenhouse gas, decreases.
This methane decrease is relatively longer lived (about 10 years) and leads to a (small) ozone decrease on the same time scale.
Impacts on UV at ground level
increase in the tropospheric ozone column due to subsonic aviation leads to a reduction in the
amount of ultraviolet radiation (UV) reaching the surface.
Impacts on acidification and eutrophication
The emitted sulphur and nitrogen compounds are removed from the atmosphere through
scavenging by precipitation (acid rain) and by dry deposition at the earth's surface.
This constitutes a small, but non-negligible, contribution to
acidification and eutropication.
Impacts on climate
- Ozone, CO2, and water vapour are greenhouse gases and their increase
has a warming effect.
- Methane is also a greenhouse gas and its decrease
has a cooling effect.
- Aerosols (sulfate particles, soot) could have a cooling effect.
- Contrails formed due to the emission of water vapour increase
the cloud cover in the upper troposphere. Contails lead
to a reduction of the solar radiation reaching the surface (surface cooling) but
they also enhance the greenhouse effect (surface warming) by absorbing longwave radiation
welling up from the earth and atmosphere below.
This might result in net cooling or
heating depending on the size and optical depth of the ice crystals of which
the contrails consist. Contrails thus lead to surface warming at night and generally to
surface cooling at daytime.
Presently it is estimated that contrails lead to a net warming effect over the full day.
- There may be changes in (non-contrail) upper level clouds:
Most contrails decay after minutes to hours, but some continue
to exist and are then not distinguishable anymore from natural
cirrus clouds (thin upper level ice clouds) for the human eye.
The climate effect of changes in cirrus cloud cover due to aviation are very uncertain.
Note on metrics for climate change
The subject of metrics is much debated recently.
Traditionally, the climate impact of emissions is expressed in terms of radiative forcing and
Global Warming Potentials (GWPs),
see e.g. the IPCC assessments
GWP corresponds to radiative forcing integrated over a certain
time interval. The chosen time horizon for GWPs is somewhat arbitrary, but usually set to 100 years.
An alternative metric is for instance the Global Temperature Potential (GTP).
Some scientists are now starting to realize that the metric to be chosen depends on the
target that has to be achieved.
This is where policymakers come into play. A target
canot be chosen without consulting policymakers.
GTP would be a metric suitable for the target that the global temperature
increase should not exceed 2 degrees.
However, depending on the chosen target many other metrics are possible.
Some scientists have suggested to include the rate of temperature change in the metric;
others, living in coastal areas, may be interested to include sea level rise
in the metric.
One might even want to formulate a metric in terms of the financial costs of
climate change damages, mitigation and adaptation.
Another important discussion point is whether a discount rate should be applied.
Note that the 4th assessment report of IPCC (AR4) recommends that Radiative Forcing Index
(RFI, the ratio between radiative forcings of different emissions)
should not be used as a metric, since it does not account for the different lifetimes of
the different emitted species
(see P. Forster, K. Shine and N. Stuber (2006) "It is premature to include non-CO2 effects of aviation in emission trading schemes", Atmospheric Environment 40(6), p. 1117,
Hence, the use of the RFI factor of 2.7 as a multiplier to quantify the full
(apart from changes in upper level clouds)
climate impact of aviation emissions
to the climate impact of only aircraft CO2
emissions is not valid.
observed over De Bilt in a high pressure situation.
Research done at KNMI
- Aircraft effects upon the atmosphere are studied by KNMI in narrow cooperation with other international, mainly European, research groups, and funded by the European Union (EU):
- In the framework
EU Environment and Climate Programme project Aeronox first estimates of the effects of emissions of nitrogen
oxides by aircraft upon the global atmospheric composition have been made in the first half of the 1990s.
- Within the EU projects POLINAT 1 and 2 (1994-1997) model calculations were confronted with measurements
made by the research aircraft Falcon in the North Atlantic Flight Corridor.
Further studies, evaluations and intercomparisons of global atmospheric chemistry models, such as our TM-model,
were performed in the EU projects AEROCHEM-2 (Modelling of the impact on ozone and other chemical compounds in the atmosphere from airplane emissions, 1998-2000).
- In the EU TRADEOFF (Aircraft emissions: Contributions of Various Climate Compounds to Changes in Composition and Radiative Forcing- Tradeoff to Reduce Atmospheric Impact, 2000-2003)
project an update on the radiative forcing estimates of the IPCC special report was calculated.
In the most recent EU project QUANTIFY
the impacts of aviation, shipping and road traffic on climate have been quantified and compared.
- At the
national level we have contributed to the bill Air Pollution and Aviation
(Nota Luchtverontreiniging en Luchtvaart - Lulu, 1995).
This bill is now somewhat outdated and nnot available on the internet anymore.
The most recent document describing the national policy of the Netherlands is the
"Luchtvaartnota" of april 2009.
- We have contributed to the environmental and climate modules of the integrated assessment model AERO
(Aviation Emissions and evaluation of Reduction Options), see e.g. S. Vlek and M. Vogels in
Air & Space Europe, Volume 2, Issue 3, p. 41-44, May-June 2000
"Interim report on the KNMI contributions to the second phase of the AERO-project",
by Wauben et al., 1995,
"Environmental and climatic consequences of aviation : final report of the KNMI contributions to the AERO-project" by Wauben et al. (1997).
- Ernst Meijer has performed a
Ph.D. study on the impact of aviation on the atmosphere. Amongst others, he incorporated a
parametrization of subgrid aircraft plume processes in our
global atmospheric chemistry model TM.
This resultied in a reduction by about 20-30 percent of the ozone perturbation due to aircraft NOx-emissions relative to the case
where the NOx-emissions are directly emitted into grid cells of the global TM model.
His Ph.D. thesis (defended 21 november 2001 at Eindhoven University of Technology) can be
downloaded from KNMI publications.
Zie ook het persbericht.
KNMI co-organized the first international presentation of the "IPCC special report
on Aviation and the Global Atmosphere" in Amsterdam in 1999 (together with NLR)
the second International Conference on Transport, Atmosphere and Climate TAC-2 in 2009 (together with DLR).
- Some first statements about the effects of
aircraft emissions on the atmosphere can be found in the excecutive summary of "The scientific assessment of ozone depletion : 1994"
- Brasseur et al. (1998) published a "European scientific assessment of the atmospheric effects of aircraft emissions"
in Atmospheric Environment, Vol. 32, No. 13, p. 2329-2418, 1998.
This was intended to serve as input to:
- The IPCC special report
on Aviation and the Global Atmosphere (1999)
- SPM (Summary for PolicyMakers).
- The IPCC 1999 input Technical reports on supersonic scenarios should be available from NASA ...
- Press release (in Dutch) about a symposium
held in Amsterdam on 23/24 June 1999 to present the IPCC special report to
the aviation sector and policy makers.
on the results from the EU Tradeoff project, Sausen et al., provided an update for 2000 of the radiative forcing estimates
from IPCC 1999, published
in Meteorologische Zeitschrift (Vol. 14, No. 4, 555-561, August 2005) .
- Most recently, the 4th assessment report of IPCC
summarized the present state of knowledge about
Contrails and Aircraft-Induced Cloudiness in section 2.6 and about radiative forcing
in section 2.9.
- The EU project ATTICA has produced a
published in Atmospheric Environment (Lee et al., 2009).
Further reading in Dutch / Meer lezen in het Nederlands
- Grootschalige verspreiding van vliegtuigemissies in de troposfeer en stratosfeer
- relevante fysische processen, Van Velthoven e.a., Tijdschrift Lucht, 12e
jaargang, nr. 4, December 1995, p. 129-133 (pdf).
- Klimaat- en milieueffecten van mondiaal vliegverkeer, Van Velthoven
e.a., Nederlands Tijdschrift
voor Natuurkunde 62/5,
p. 71-75, 19 maart 1996 (pdf, samenvatting).
- Zelf rekenen aan strepen in de lucht, D. Olivie, Natuur en Techniek,
Juli/Augustus 2000, 58-62.
- Ministerie van Verkeer en Waterstaat over
Milieu en geluid luchtvaart. Hier staat ook de laatste luchtvaartnota
d.d. 17 april 2009.
- Milieucentraal adviseert over klimaatvriendelijk
Further reading in English
- See the assessments listed above.
- The impact of NOx emissions from aircraft upon the atmosphere at flight
altitudes 8-15 km, AERONOX, ed. U. Schumann.
Office for Publications of the European Commission, Brussels (1995), pp. 471.
- Pollution from Aircraft Emissions in the North Atlantic Flight
Corridor (POLINAT), ed. U. Schumann.
Air Pollution Research Report 58, Report EUR 16978 EN, Luxembourg:
Office for Official Publication of the European Communities (1997)
- Pollution from Aircraft Emissions in the North Atlantic Flight Corridor
(POLINAT 2), edited by U. Schumann, Air Pollution Research Report 68,
Report EUR 18877 EN, Luxembourg: Office for Official Publication of the
European Communities, ISBN 92-828-6197-X (1999) pp. 312.
- Also of interest are the proceedings of the international scientific conferences
on Aviation, Atmosphere and Climate (AAC) and on Transport, Atmosphere and Climate (TAC-1 and TAC-2) organized by DLR and partners:
- AAC (30 June-3 July 2003, Friedrichshafen at Lake Constance,
Germany): R. Sausen, C. Fichter and G. Amanatidis (Eds.), 2004:
European Conference on: Aviation, Atmosphere and Climate
(AAC): Proceedings of an International Conference.
Air pollution research report 83, European Commission,
See also Meteorologische Zeitschrift, Volume 14, Number 4, August 2005 (contents).
- TAC-1 (26-29 June 2006, Oxford):
Sausen, R., A. Blum, D.S. Lee and C. Bruning, (Eds.) 2007: Proceedings of an International Conference on
Transport, Atmosphere and Climate (TAC). Luxembourg, Office for Official Publications of the European Communities, ISBN 92-79-04583-0, 320pp.
- TAC-2 (22-25 June 2009; Aachen, Germany, and Maastricht, the Netherlands): proceedings are in preparation
- An overview of measurements and modelling of the impact of aviation
emissions on the atmosphere was given by Van Weele et al. in the KNMI Climate Research Department's Biennal Review (1999).
Other websites with information about the effects of aircraft emissions:
Other websites with information about contrails: