European Geosciences Union, Atmospheric Measurement Techniques, 2(3), p. 407-427, 2010
European Geosciences Union, Atmospheric Measurement Techniques Discussions, 5(2), p. 2587-2637
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Quasi-continuous, in-situ measurements of atmospheric CO 2 , O 2 /N 2 , CH 4 , CO, N 2 O, and SF 6 have been performed since August 2005 at the tall tower station near Bialystok, in Eastern Poland, from five heights up to 300 m. Besides the in-situ measurements, flask samples are filled approximately weekly and measured at Max-Planck Institute for Biogeochemistry for the same species and, in addition, for H 2 , Ar/N 2 and the stable isotopes 13 C and 18 O in CO 2 . The in-situ measurement system was built based on commercially available analysers: a LiCor 7000 for CO 2 , a Sable Systems "Oxzilla" FC-2 for O 2 , and an Agilent 6890 gas chromatograph for CH 4 , CO, N 2 O and SF 6 . The system was optimized to run continuously with very little maintenance and to fulfill the precision requirements of the CHIOTTO project. The O 2 /N 2 measurements in particular required special attention in terms of technical setup and quality assurance. The evaluation of the performance after more than three years of operation gave overall satisfactory results, proving that this setup is suitable for long term remote operation with little maintenance. The precision achieved for all species is within or close to the project requirements. The comparison between the in-situ and flask sample results, used to verify the accuracy of the in-situ measurements, showed no significant difference for CO 2 , O 2 /N 2 , CH 4 and N 2 O, and a very small difference for SF 6 . The same comparison however revealed a statistically significant difference for CO, of about 6.5 ppb, for which the cause could not be fully explained. From more than three years of data, the main features at Bialystok have been characterized in terms of variability, trends, and seasonal and diurnal variations. CO 2 and O 2 /N 2 show large short term variability, and large diurnal signals during the warm seasons, which attenuate with the increase of sampling height. The trends calculated from this dataset, over the period August 2005 to December 2008, are 2.02±0.46 ppm/year for CO 2 and −23.2±2.5 per meg/year for O 2 /N 2 . CH 4 , CO and N 2 O show also higher variability at the lower sampling levels, which in the case of CO is strongly seasonal. Diurnal variations in CH 4 , CO and N 2 O mole fractions can be observed during the warm season, due to the periodicity of vertical mixing combined with the diurnal cycle of anthropogenic emissions. We calculated increase rates of 10.1±4.4 ppb/year for CH 4 , (−8.3)±5.3 ppb/year for CO and 0.67±0.08 ppb/year for N 2 O. SF 6 shows only few events, and generally no vertical gradients, which suggests that there are no significant local sources. A weak SF 6 seasonal cycle has been detected, which most probably is due to the seasonality of atmospheric circulation. SF 6 increased during the time of our measurement at an average rate of 0.29±0.01 ppt/year.