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

International audienceA one-year time series of continuous atmospheric CO2 measurements from Bern, Switzerland is presented. O2/N2 and Ar/N2 ratios as well as stable carbon and oxygen isotopes of CO2 and ?29N2, ?34O2 and ?36Ar were measured periodically in a continuous way 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 CO2 and 222Rn 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 ?13C and ?18O of source CO2 throughout the year, however, with generally lower values in winter compared to summertime. The O2:CO2 oxidation ratio during the nighttime build-up of CO2 varies between ?0.96 and ?1.69 mol O2/mol CO2. Furthermore, Ar/N2 measurements showed that artifacts like thermal fractionation at the air intake are relevant for high precision measurements of atmospheric O2