Mid-infrared dual-comb spectroscopy of volatile organic compounds across long open-air paths

Open-path measurements of atmospheric gas species in the air, including volatile organic compounds, are essential to quantify emissions from sources like oil and gas, forest fires, and industry. Here, we extend open-path dual-comb spectroscopy to probe the fundamental mid-infrared C-H stretch modes of volatile organic compounds over up to 1 km long open-air paths. The spectrometer’s high resolution and accuracy facilitates suppression of strong spectral clutter from atmospheric water and methane, allowing quantitative measurements of released acetone and isopropanol with a 1−σ sensitivity of 5.7  ppm·m and 2.4  ppm·m, respectively, and of ambient atmospheric ethane with a 1−σ sensitivity of 0.4 ppb, measured with 1 min time resolution over hours. These results underline the potential of dual-comb spectroscopy for quantifying emissions.