Open-path dual-comb spectroscopy for multispecies trace gas detection in the 4.5-5 µm spectral region Laser & Photonics Reviews

Open-path dual-comb spectroscopy provides multispecies atmospheric gas concentration measurements with high precision. Here, open-path dual-comb spectroscopy is extended to the mid-infrared 5 µm atmospheric window, enabling atmospheric concentration retrievals of the primary greenhouse gases, N2O, CO2, and H2O, as well as the criteria air pollutants O3 and CO across 600 m and 2 km round-trip paths. Measurements are demonstrated over a five-day period at 2 min temporal resolution with 80% uptime. The achieved precision is sufficient to resolve the atmospheric concentration variations of the multiple gas species; retrieved dry mixing ratios of CO and N2O are in good agreement with a colocated point sensor. In addition, the retrieved ratio of excess CO versus CO2 agrees with similar urban studies but disagrees with the US National Emission Inventory by a factor of 3. The retrieved ratio of excess N2O versus CO2 exhibits a plume-dependent value, indicating the variability of sources of the greenhouse gas N2O.