Measurements of CO2, its stable isotopes, O2/N2, and 222Rn at Bern, Switzerland

A one-year time series of atmospheric CO2 measurements from Bern, Switzerland, is presented. O-2/N-2 and Ar/N-2 ratios as well as stable carbon and oxygen isotopes of CO2 and delta N-29(2), delta O-34(2) and delta Ar-36 were measured periodically during a one year period. Additionally, the Rn-222 activity was measured during three months in the winter 2004. Using the correlation from short-term fluctuations of CO2 and Rn-222 we estimated a mean CO2 flux density between February 2004 and April 2004 in the region of Bern of 95 +/- 39 tC km(-2) month(-1). The continuous observations of carbon dioxide and associated tracers shed light on diurnal and seasonal patterns of the carbon cycle in an urban atmosphere. There is considerable variance in nighttime delta C-13 and delta O-18 of source CO2 throughout the year, however, with generally lower values in winter compared to summertime. The O-2:CO2 oxidation ratio during the nighttime build-up of CO2 varies between -0.96 and -1.69 mol O-2/mol CO2. Furthermore, Ar/N-2 measurements showed that artifacts like thermal fractionation at the air intake are relevant for high precision measurements of atmospheric O-2.