An automated time-integrating chamber system with offline gas analysis to monitor N2O fluxes and isotopic composition in agricultural ecosystems

Static chambers are the predominating method for measuring N₂O emissions from agricultural ecosystems and thus provide the basis for deriving corresponding emission factors. In order to obtain representative N₂O emission values, long-term measurements (one to several years) are necessary that cover relevant short-term variations including pulse-like emissions after fertilizer application or rainfalls. This is often a problem for the widely used manual chamber measurements that are typically applied in weekly or fortnightly intervals. Fully automated chamber systems, on the other hand, can provide continuous measurements over longer time periods, but are cost-extensive as they require online (on-site) gas analysis.

To overcome this problem, we constructed an (non-steady-state) automated time integrating chamber system (ATIC) that can sample at intervals of a few hours but accumulates the flux signal over many chamber closure cycles. During each 15-min chamber closure phase, small air samples are collected every 3.5 min and accumulated in four different gas bags. After typically one week the gas bags are brought to the lab for analysis. The accumulated samples in the four bags represent a time-averaged concentration increase that is used to calculate weekly time-integrated gas emission fluxes. In addition, the system can be used for analyzing the isotopic composition of the emitted N₂O in order to determine the underlying source process.

The ATIC systems, that can run on battery power, were successfully applied in two long-term field experiments (> 2 years) for N₂O emission monitoring on grassland, as well as studying changes in emission fluxes and isotopic composition of urine patches over a few months. We will show the setup of the system, the quality control of the data and discuss the resulting N₂O emission data and major contributing processes.