Measurements of CO 2, its stable isotopes, O 2/N 2, and 222Rn at Bern, Switzerland
A one-year time series of atmospheric CO 2 measurements from Bern, Switzerland, is presented. O 2/N 2 and Ar/N 2 ratios as well as stable carbon and oxygen isotopes of CO 2 and δ 29N 2, δ 34O 2 and δ 36Ar were measured periodically during a one year period. Additionally, the 222Rn activity was measured during three months in the winter 2004. Using the correlation from short-term fluctuations of CO 2 and 222Rn we estimated a mean CO 2 flux density between February 2004 and April 2004 in the region of Bern of 95±39 tC km –2month –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 δ 13C and δ 18O of source CO 2 throughout the year, however, with generally lower values in winter compared to summertime. The O 2:CO 2 oxidation ratio during the nighttime build-up of CO 2 varies between –0.96 and –1.69 mol O 2/mol CO 2. 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.