Open-path anti-pollution multi-pass cell-based TDLAS sensor for the online measurement of atmospheric H 2 O and CO 2 fluxes.

We report an open-path and anti-pollution multi-pass cell based tunable diode laser absorption spectroscopy (TDLAS) sensor, which was designed for online measurement of atmospheric HO and CO fluxes. It is mainly composed of two plano-convex mirrors coated on a convex surface, which makes it different from traditional multi-pass cells. This design does not allow a direct contact between the coating layer of the lens and air, thereby realizing the anti-pollution effect of the coating layer. Two DFB lasers operating at 1392 nm and 2004 nm were employed to target HO and CO absorption lines, respectively. Allan analysis of variance indicated that detection limits of HO and CO were 5.98 ppm and 0.68 ppm, respectively, at an average time of 0.1 s. The sensor performance was demonstrated by measuring CO and HO flux emissions at Jiangdu Agricultural Monitoring Station in Jiangsu Province. The results were compared with those obtained using the commercial instrument LI-7500, which is based on non-dispersive infrared technology. The developed gas analysis instrument exhibited good consistency with commercial instruments, and its accuracy was comparable; thus, it has strong application prospects for flux measurements in any ecosystem.