Measuring system for the long-term monitoring of biosphere/atmosphere exchange of carbon dioxide

We describe an ongoing program being carried out in Hungary to investigate the role of the temperate continental region ill the global carbon cycle. C arbon dioxide mixing ratios are continuously monitored at 10, 48, 82, and 1 15 rn above the ground on a television transmitter tower, and the atmospher e/surface exchange of CO2 is measured by eddy covariance at 82 m. The regio n surrounding the tower is typical of rural areas of central Europe, with a gricultural fields, forest patches, and small villages. We first describe t he layout and the operation of the measuring system designed for the contin uous, unattended monitoring: of the vertical distribution of CO2 mixing rat io in the lowest 115 m of the atmosphere based on a Li-Cor model 6251 infra red gas analyzer (IRGA). It provides vertical profile data with a temporal resolution of 8 min. Next, we discuss the measuring system for long-term, c ontinuous monitoring of the biosphere/atmosphere exchange of CO2. The eddy correlation system is based on a Li-Cor model 6262 fast-response IRGA and a Gill ultrasonic anemometer running at 4 Hz sampling frequency. Results are to illustrate the performance of the systems. Among others, they show the occasional accumulation of CO2 in the boundary layer in the Carpathian Basi n during winter and the diurnal variation of the vertical distribution of C O2 mixing ratio in summer. A simple method based on similarity theory to ca lculate vertical fluxes from vertical gradients is presented, which can be used to fill the data gaps that inevitably occur during long-term eddy corr elation measurements. The present study confirms the feasibility of the lon g-term tall-tower CO2 flux and mixing ratio measurements.