Carbon dioxide flux in the centre of ?ód?, Poland-analysis of a 2-year eddy covariance measurement data set

摘要

Continuous measurements of carbon dioxide turbulent flux FCO2 carried out with the eddy covariance method have been made in ?ód? since FCO2 July 2006. The measurement point (Lipowa Station) is located in the west part of the densely built-up city centre, where artificial surfaces clearly prevail over natural terrain. The measurement system includes a Kipp and Zonen's (Delft, Holland) CNR1 net radiometer, RMYoung (Traverse City, Michigamn, USA) 81000 sonic anemometer and Li-cor (Lincoln, Nebraska, USA) 7500 open path H2O/CO2 infrared gas analyser. Sensors are installed on the high tower 20 m above the roof of the building and 37 m above the ground, so the measurement height exceeded the urban canopy layer more than twice. The diurnal and annual variability of carbon dioxide flux for the period July 2006 to August 2008 is analysed in the article. The results show the characteristic features in diurnal and annual courses of FCO2. Independently from the season, positive (upward) fluxes of the order of 0-15 μmol m-2 s-1 prevail in the data. During the cold season, an increase in turbulent CO2 exchange is observed (FCO2 quite often exceeded 30 μmol m-2 s-1). This can be attributed to anthropogenic CO2 emissions, which are particularly strong in winter due to, among other things, mineral fuel combustion during domestic heating. The average monthly fluxes are positive in all seasons, which means that emission of CO2 in the surroundings of the measurement point prevails over its uptake. Apart from the season, the maximum flux occurred during the day and the minimum during the second part of the night. Wintertime monthly averaged fluxes are much higher than summertime ones. The observed increase in CO2 exchange during weekdays in comparison with weekends can be caused by the weekly rhythm of traffic in the surroundings of Lipowa Station.