Open-Path Dual-Comb Spectroscopy for Multispecies Trace Gas Detection in the 4.5-5 μm Spectral Region

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 mu m atmospheric window, enabling atmospheric concentration retrievals of the primary greenhouse gases, N2O, CO2, and H2O, as well as the criteria air pollutants O-3 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.

Automated summary

Open-path dual-comb spectroscopy has been extended to the mid-infrared 5 µm atmospheric window, enabling high precision measurements of multispecies atmospheric gas concentrations, including primary greenhouse gases and criteria air pollutants. The retrieved ratios of excess CO versus CO2 and N2O versus CO2 show variations and discrepancies with previous studies and emission inventories.