 |
| Titel |
Seasonal and annual variation of carbon dioxide surface fluxes in Helsinki, Finland, in 2006–2010 |
| VerfasserIn |
L. Järvi, A. Nordbo, H. Junninen, A. Riikonen, J. Moilanen, E. Nikinmaa, T. Vesala |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 18 ; Nr. 12, no. 18 (2012-09-21), S.8475-8489 |
| Datensatznummer |
250011458
|
| Publikation (Nr.) |
 copernicus.org/acp-12-8475-2012.pdf |
|
|
|
|
|
| Zusammenfassung |
Five years of carbon dioxide exchange measured with the eddy covariance
technique at the world's northernmost urban flux station SMEAR III located
in Helsinki, Finland, were analyzed. The long-term measurements and
high-latitude location enabled us to examine the seasonal and annual
variations of CO2 exchange, and to identify different factors
controlling the measured exchange. Online traffic counts and soil
respiration measurements were utilized in the study. Furthermore, the
advantage of the station is that the complex surrounding area enables us to
distinguish three different surface cover areas that can be evaluated
separately. We also tested different methods (artificial neural networks and
median diurnal cycles) to fill gaps in CO2 flux time series and
examined their effect on annual emission estimates.
The measured fluxes were highly dependent on the prevailing wind direction
with the highest fluxes downwind from a large road and lowest downwind from
the area of high fraction of vegetation cover. On an annual level, the area
of the road emitted 3500 g C m−2 whereas the area of high fraction of
vegetation cover emitted only 870 g C m−2 showing the effect of surface
cover to be large in urban areas. Seasonal differences in the CO2
exchange downwind from the road were mainly caused by reduced traffic rates
in summer, whereas in other directions seasonality was more determined by
vegetation activity. Differences between the gap filling methods were small,
but slightly better (0.6 μmol m−2 s−1 smaller RMSE) results
were obtained when the artificial neural network with traffic counts was
used instead of the one without traffic network and method based on median
diurnal cycles. The measurement site was a net carbon source with
average annual emissions of 1760 g C m−2, with a biased error of
6.1 g C m−2 caused by the gap filling. The annual value varied 16%
between the different years. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|