To measure field scale N2O and CO2 emissions a 3.2 m ´ 96 m aluminium liner structure of 0.8 m height is installed which is enclosed with a plastic cover to get an airtight measuring tunnel (triangular profile). Beneath the tunnel soil emissions are integrated over a 306 m2 area and during several hours. N2O, CO2, CH4 (and H2O) concentrations are continuously measured by path-averaged infrared spectroscopy (FTIR) through the whole measuring tunnel. The trace gas concentration measurement is performed as near as possible to the soil surface (about 10 – 20 cm) by the open path (K300 spectrometer; Haus et al., 1994) in the middle of the tunnel. The IR radiation source is located at the opposite edge of the measuring tunnel. The telescope of the spectrometer has a diameter of 15 cm and a visual angle of 3 mrad to secure not to interrupt the radiation path due too soil or plastic cover irregularities. The operation of the FTIR spectrometer requires a weather protected surrounding.
Around the measuring tunnel a small trench of about 10 cm depth was excavated in order to fix the plastic cover at the soil and not at the grass. Sand-filled tubes are used to fix the plastic cover at the soil and at the liner structure. The plastic cover is of 8 m width and 50 m length. In order to get a closed system the two parts of the cover have been overlapped folded by one meter.
The detections limits and measurement accuracies of the FTIR spectrometry are appropriate to detect concentration increases of more than 1 % within the tunnel during up to 10 hours.
Contact: , Carsten Jahn