Download Impact of transport emissions on the lower atmosphere

16 July 2009
Impact of transport emissions on the lower atmosphere
Traffic emissions cause a number of damaging chemical changes in the atmosphere. A recent
study has estimated the impact of road, aircraft and ship emissions on the atmosphere’s
chemical make-up in terms of ozone and the hydroxyl radical OH.
Traffic emissions form a large part of EU air pollution and are the subject of climate change policy1. Ozone pollution in
the troposphere adversely affects human health and damages vegetation including crops, but it also behaves as a potent
greenhouse gas (GHG). It occurs naturally but is also formed by the interaction of sunlight with pollutants emitted by
transport and industry.
This recent study was conducted as part of the EU Integrated Project QUANTIFY 2. Six different atmospheric chemistry
models were applied in order to estimate the impact of emissions from road transport, aviation and shipping on ozone.
The impact on the hydroxyl radical OH was also estimated. OH is a natural constituent of the atmosphere which has been
referred to as the “detergent” of the troposphere because it removes pollutants and GHGs such as methane and carbon
monoxide.
The results indicate that, the largest impact from total traffic emissions on total ozone occurs in the summer in the
northern hemisphere. The greatest impact extends from the eastern US over the Atlantic to western Europe. In the
southern hemisphere, changes are about 50 per cent lower than in the northern hemisphere.
Ship emissions have the greatest effect on the lower troposphere, causing over half of transport-induced changes in
ozone in some regions. Notably, the effect of aircraft emissions does not dominate globally at the upper troposphere, but
dominates the effect of traffic on ozone in the tropopause region (the boundary between the troposphere and the
stratosphere) north of 30°N. Road traffic also strongly affects the northern upper troposphere, especially during the
northern summer. During northern winter, the relative contributions from each traffic sector are all about the same.
Ship emissions have the largest impact on global OH at the lower troposphere and, therefore, the largest impact on
reducing methane lifetime as they are released in relatively clean regions over the sub-tropical and tropical oceans where
OH is highly sensitive to traffic emissions.
The study also considered the possible impact of ozone and methane on climate change by quantifying the associated
radiative forcing (RF). RF is a measure of the imbalance between incoming radiation and outgoing radiation caused by a
disruption of the atmosphere’s composition. Positive RF leads to a warming and negative RF causes a cooling.
Road emissions and aircraft emissions both caused positive forcing overall, with road emissions having the largest
impact. Shipping’s effect on OH and methane caused negative RF, indicating that its climate forcing impact through
additional ozone formation was more than compensated for by its impact on OH and the resulting destruction of
atmospheric methane. However shipping emissions have several adverse effects such as the impact of NOx, NO2 and
SO2 emissions on eutrophication, health and acidification. The EU strategy to reduce emissions from ships3 sets out
actions to reduce these negative impacts.
1. See http://ec.europa.eu/environment/air/transport/sustainable.htm
2. QUANTIFY (Quantifying the Climate Impact of Global and European Transport Systems) was supported by the European Commission under the
Sixth Framework Programme. See www.pa.op.dlr.de/quantify
3 See http://ec.europa.eu/environment/air/transport/ships.htm
Source: Hoor, P., Borken-Kleefeld, J. Caro, D. et al. (2009). The impact of traffic emissions on atmospheric ozone and OH: results from QUANTIFY.
Atmospheric Chemistry and Physics. 9: 3113-3136.
Contact: [email protected]
Theme(s): Air pollution, Climate change and energy
Additional information: Information on successful LIFE projects that have contributed to reduce traffic emissions can be found in the urban transport
section of the LIFE website: http://ec.europa.eu/environment/life/themes/urban/documents/urban_transport.pdf
Opinions expressed in this News Alert do not necessarily reflect those of the European Commission
To cite this article/service: "Science for Environment Policy": European Commission DG Environment News Alert Service, edited by
SCU, The University of the West of England, Bristol.
European Commission DG ENV
News Alert Issue 160
July 2009
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