Measurements of CO2, its stable isotopes, O2/N 2, and222Rn at Bern, Switzerland

Abstract

A one-year time series of atmospheric CO2 measurements from Bern, Switzerland, is presented. O2/N2 and Ar/N 2 ratios as well as stable carbon and oxygen isotopes of CO 2 and δ29N2, δ34O 2 and δ36 Ar 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 CO2 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-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 O 2:CO2 oxidation ratio during the nighttime build-up of CO2 varies between -0.96 and -1.69 mol O2/mol CO 2. Furthermore, Ar/N2 measurements showed that artifacts like thermal fractionation at the air intake are relevant for high precision measurements of atmospheric O2.