Development of a field-deployable method for simultaneous, real-time measurements of the four most abundant N_2O isotopocules

摘要

Understanding and quantifying the biogeochemical cycle of N2O is essential to develop effective N2O emission mitigation strategies. This study presents a novel, fully automated measurement technique that allows simultaneous, high-precision quantification of the four main N2O isotopocules ((NNO)-N-14-N-14-O-16, (NNO)-N-14-N-15-O-16, (NNO)-N-15-N-14-O-16 and (NNO)-N-14-N-14-O-18) in ambient air. The instrumentation consists of a trace gas extractor (TREX) coupled to a quantum cascade laser absorption spectrometer, designed for autonomous operation at remote measurement sites. The main advantages this system has over its predecessors are a compact spectrometer design with improved temperature control and a more compact and powerful TREX device. The adopted TREX device enhances the flexibility of the preconcentration technique for higher adsorption volumes to target rare isotope species and lower adsorption temperatures for highly volatile substances. All system components have been integrated into a standardized instrument rack to improve portability and accessibility for maintenance. With an average sampling frequency of approximately 1 h(-1), this instrumentation achieves a repeatability of 0.09, 0.13, 0.17 and 0.12 parts per thousand for N-15, N-15, O-18 and site preference of N2O, respectively, for pressurized ambient air. The repeatability for N2O mole fraction measurements is better than 1 ppb (parts per billion, 10(-9) moles per mole of dry air).