Mid-infrared IPDA lidar for probing atmospheric toluene concentration

Aiming at the real-time detection of toluene concentration in the atmosphere, an integrated-path differential absorption (IPDA) lidar is proposed based on inter-band cascade lasers. Since the C-H bond of toluene has a slowly-changing absorption spectrum in the mid-infrared band, this IPDA lidar is designed using 2935.5cm^-1 and 3192.0cm^-1 as the operating wavelength by considering the influence of the main interfering gases such as H₂O, CH₄, and HCl. A spectroscopic system with a mid-infrared diffraction grating is configured to realize synchronous detection of dual-wavelength received signals. A retrieval algorithm and its error analysis model for atmospheric toluene concentration are presented. And then the performance of lidar is analyzed and discussed under the conditions of different visibilities, path lengths, and water vapor concentrations by combining with the mid-latitude standard atmospheric model. These results show that the relative error of toluene concentration is less than 10% within the concentration range of 20ppb to 10ppm under the condition of atmospheric visibility of 5km, path length of 1.6km, and the water vapor concentration of less than 0.4%. This IPDA lidar can provide an effective scheme for real-time detection of atmospheric toluene concentration.