Site selective real-time measurements of atmospheric N2O isotopomers by laser spectroscopy

[摘要] We describe the first high precision real-time analysis of the N₂Osite-specific isotopic composition at ambient mixing ratios. Our techniqueis based on mid-infrared quantum cascade laser absorption spectroscopy(QCLAS) combined with an automated preconcentration unit. The QCLAS allowsfor simultaneous and specific analysis of the three main stable N₂Oisotopic species, ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O,¹⁴N¹⁴N¹⁶O, and the respective site-specific relative isotoperatio differences δ¹⁵N^α and δ¹⁵N^β. Continuous, stand-alone operation is achieved by usingliquid nitrogen free N₂O preconcentration, a quasi-room-temperaturequantum cascade laser (QCL), quantitative sample transfer to the QCLAS andan optimized calibration algorithm. The N₂O site-specific isotopiccomposition (δ¹⁵N^α and δ¹⁵N^β)can be analysed with a long-term precision of 0.2‰. The potential of thisanalytical tool is illustrated by continuous N₂O isotopomermeasurements above a grassland plot over a three week period, which allowedidentification of microbial source and sink processes.

[学科分类] 几何与拓扑