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From
•>>July 2005
Andreas Stohl answers
a few questions about this month's fast moving front in the
field of Geosciences.
Field: Geosciences
Article: A textbook example of long-range transport: Simultaneous observation of ozone maxima of stratospheric and North American origin in the free troposphere over Europe
Authors: Stohl,
A;Trickl, T
Journal: J GEOPHYS RES-ATMOS, 104: (D23) 30445-30462, DEC 20 1999
Addresses:
Univ Munich, Lehrstuhl Bioklimatol & Immiss Forsch, Hochanger 13, D-85354 Freising, Germany.
Univ Munich, Lehrstuhl Bioklimatol & Immiss Forsch, D-85354 Freising, Germany.
Fraunhofer Inst Atmosphar Umweltforsch, IFU, D-82467 Garmisch
Partenkirchen, Germany.
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Why do you think your
paper is highly cited?
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“Interest in intercontinental transport has since then risen dramatically because emission controls taken at one place can be rendered relatively ineffective if emissions in other parts of the world are increasing.”
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The paper presents the first clear attribution of ozone that
was measured over Europe to photochemical production over North
America and, thus, to intercontinental air pollution transport. At
the same time, the transport mechanism that was described turned
out to be typical for intercontinental air pollution transport,
not only from North America to Europe but also from Asia to North
America. In the meantime, many such cases have been discovered,
thus yielding a relatively high citation rate for our paper.
Does it describe a new discovery or new methodology that's
useful to others?
It was discovered that ozone concentrations of the order of 100
ppb over Europe can be entirely due to photochemical production
over North America. If measured at the surface, this ozone
concentration would have led to the exceedance of European air
quality standards.
Could you summarize the significance of your paper in
layman's terms?
The significance lies in its first clear detection of pollution
ozone from North America over Europe. Furthermore, it turned out
later that the transport mechanism responsible in the
intercontinental transport of ozone was typical, not only for
pollution transport from North America to Europe but also from
Asia to North America. Interest in intercontinental transport has
since then risen dramatically because emission controls taken at
one place can be rendered relatively ineffective if emissions in
other parts of the world are increasing. Thus, ozone
concentrations (but also other pollutant concentrations, such as
those of particulates) can be increasing even though precursor
emissions are being reduced. Ozone concentrations are still
increasing in many parts of the world and it seems that
intercontinental transport from Asia and other regions where
emissions are still growing could be the reason for this
still-debated trend.
How did you become involved in this research?
We were studying the transport of ozone from the stratosphere
(thus, natural ozone) to the lower troposphere. Thomas Trickl
turned on his lidar (LIght Detection And Ranging) to measure such
an event and we indeed found high ozone concentrations in the
lidar data. However, it turned out that only some of the ozone
(ironically the ozone at low altitudes) was of stratospheric
origin. Other pockets with high ozone concentrations could not be
explained by a stratospheric source but instead were found to be
coming from North America. Co-incidental measurements taken
onboard a commercial aircraft over the North Atlantic, and ozone
monitoring at the North American east coast confirmed our
findings.
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Andreas Stohl
Norwegian Institute for Air Research (NILU)
Department of Regional and Global Pollution Issues
Kjeller, Norway
Thomas Trickl
Forschungszentrum Karlsruhe, IMK-IFU
Garmisch-Partenkirchen
Germany
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