Open-path Dual-comb Spectroscopy for Multispecies Trace Gas Detection in the 4.5 {\mu}m to 5 {\mu}m Spectral Region

TL;DR

This paper extends open-path dual-comb spectroscopy to the mid-infrared 5 μm region, enabling high-precision, multi-species atmospheric gas measurements over hundreds of meters to kilometers, with potential for environmental monitoring.

Contribution

The study demonstrates the first application of open-path dual-comb spectroscopy in the 5 μm spectral region for simultaneous detection of multiple greenhouse gases and pollutants over long distances.

Findings

Successful measurement of N₂O, CO₂, H₂O, O₃, and CO over 600 m to 2 km paths.

Achieved 80% uptime with two-minute resolution over five days.

Retrieved gas ratios agree with point sensors and urban studies, revealing source variability.

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 {\mu}m atmospheric window, enabling atmospheric concentration retrievals of the primary greenhouse gases, N$_2$O, CO$_2$, and H$_2$O as well as the criterion air pollutants O$_3$ 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 N$_2$O are in good agreement with a co-located point sensor. In addition, the retrieved ratio of excess CO vs CO$_2$ agrees with similar urban studies but disagrees with the US National Emission Inventory by a factor of 3. Our retrieved ratio of excess N$_2$O vs CO$_2$ exhibits a plume-dependent value, indicating the variability of sources of the greenhouse gas N$_2$O.