Fast horizontal radial plume mapping of N₂O using open-path absorption spectroscopy with a quantum-cascade laser

We demonstrate record fast horizontal radial plume mapping (HRPM) of nitrous oxide (N₂O) emissions, enabled by a quantum-cascade laser (QCL) and an open-path direct absorption spectroscopy operating around the 4.5 μm wavelength. The high signal-to-noise ratio of the system yields an atmospheric N₂O sensor with a remarkable sensitivity of 25 ppt at 1 Hz update rate as assessed through Allan deviation analysis. The excellent sensitivity translates into significantly increased measurement rates (0.2−2 kHz) of column-integrated N₂O concentrations. This is complemented by swift horizontal beam-scanning to multiple reflectors positioned in a 4 × 4 grid over a 735 m² probed area. Consequently, we achieve HRPM over the probed area with scan times as short as 9 s, marking a substantial 60-fold improvement compared to a recent benchmark in the field. The exceptional data update rate of our QCL based sensor, coupled with the rapid beam-scanning capabilities, lays the foundation for real-time generation of HRPM tomographic maps of gas concentration with scan cycles on the order of 1 s. This presents a powerful tool for expedited gas leak source localization, as well as understanding the spatial dynamics of area source emissions.