Measurements of CO 2 , its stable isotopes, O 2 /N 2 , and 222 Rn 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 29 N 2 , δ 34 O 2 and δ 36 Ar were measured periodically during a one year period. Additionally, the 222 Rn activity was measured during three months in the winter 2004. Using the correlation from short-term fluctuations of CO 2 and 222 Rn we estimated a mean CO 2 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 δ 13 C and δ 18 O 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 .