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| Titel |
Exchange of nitrous oxides and carbon dioxide measured using the eddy covariance technique in a high-latitude city |
| VerfasserIn |
Leena Järvi, Annika Nordbo, Üllar Rannik, Sami Haapanala, Mari Pihlatie, Ivan Mammarella, Anu Riikonen, Eero Nikinmaa, Timo Vesala |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094695
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| Publikation (Nr.) |
 EGU/EGU2014-10123.pdf |
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| Zusammenfassung |
| In Helsinki, Finland, carbon dioxide (CO2) fluxes have been measured continuously using the
eddy covariance (EC) technique since 2005. In summer 2012, the measurements were
supplemented with the fluxes of nitrous oxide (N2O) in order to examine how the exchanges
of these two important greenhouse gases behave in urban environment.
The EC measurements are made at the semi-urban measurement station SMEAR III
Kumpula site located four kilometres north-east from the Helsinki city centre. The
measurements are made on the top level of a 31 meters high lattice tower (60°12.17’N,
24°57.67’E) located on a hill, 26 m above sea level. The area around the tower can be divided
into three surface cover sectors: built, road and vegetation, each representing the typical
surface cover of the area. These areas allow us to examine the effect of different urban surface
covers to the exchange of CO2 and N2O. The measurement setup includes an ultrasonic
anemometer (USA-1, Metek GmbH) and a closed-path infrared gas analyzer (LI-7000,
LI-COR) to measure the CO2 flux. During the summer 2012 measurement campaign
lasting from 21 June till 27 November, the N2O flux was measured using a TDL
spectrometer. Commonly accepted procedures were used to post-process the raw 10 Hz
data.
Overall, the measurement surroundings act as a source for both CO2 and N2O. The
long-term measurements of the CO2 flux show a strong seasonal variation with clear effect
from vegetation. In summer in the direction of high fraction of vegetation cover, the CO2
uptake exceeds its emissions and a downward flux reaching on average 10 μmol m-2 s-1 is
observed. N2O on the other hand reaches its maxima values (campaign median 2.0 μmol m-2
h-1) in the same direction. This indicates that vegetation cannot be neglected in the
urban greenhouse exchange studies. Traffic had a clear role emitting both N2O
and CO2 with higher emissions during the rush hours than at other times. In the
direction of the heavily trafficked road, dependence between the two fluxes was
observed.
The annual CO2 emission calculated from five years are on average 1760 g C m-2. Most
of the emissions come from the road sector with an annual emission of 3500 g C m-2. Using
the measured emission ratio between N2O and CO2 as a proxy in this direction yielded an
annual N2O emission of 0.26 g N m-2. |
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