Open-path Dual-comb Spectroscopy for Multispecies Trace Gas Detection in the 4.5 μm to 5 μm Spectral Region
Abstract
Open-path dual-comb spectroscopy provides multi-species atmospheric gas concentration measurements with high precision. Here, we extend open-path dual comb spectroscopy 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 criterion air pollutants O3 and CO across 600 m and 2 km round-trip paths. We demonstrate measurements over a five-day period at two-minute 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 co-located point sensor. In addition, the retrieved ratio of excess CO vs CO2 agrees with similar urban studies but disagrees with the US National Emission Inventory by a factor of 3. Our retrieved ratio of excess N2O vs CO2 exhibits a plume-dependent value, indicating the variability of sources of the greenhouse gas N2O.