Tunable laser-based detection of benzene using spectrally narrow absorption features

A mid-infrared laser-based sensor for the detection of gas-phase benzene (C6H6) in ambient air is presented. It is based on the principle of tunable laser absorption spectroscopy utilizing unique fine spectral features of benzene near 3.4 µm, along with the robust design of an optical multi-pass cell. The sensor is capable of providing real-time measurement of benzene as low as 200 ppb (12 ppm m) at 2 Hz, while still being portable enough to fit in the trunk of a small car. A demonstration measurement in a moving vehicle is presented based on the data collected along Highway 101, El Camino Real, and around Stanford University campus in California, showing elevated benzene emission in several spatial regions.