Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 5 2005 10.5194/acpd-5-8473-2005 http://www.atmos-chem-phys-discuss.net/5/8473/2005/ http://www.atmos-chem-phys-discuss.net/5/8473/2005/acpd-5-8473-2005.html http://www.atmos-chem-phys-discuss.net/5/8473/2005/acpd-5-8473-2005.pdf 8473 8506 2005-09-09 Measurements of CO₂, its stable isotopes, O₂/N₂, and ²²²Rn at Bern, Switzerland P. Sturm M. Leuenberger F. L. Valentino B. Lehmann B. Ihly Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland A 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 δ²⁹N₂, δ³⁴O₂ and δ³⁶Ar 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 δ¹³C and δ¹⁸O 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.