A Dual-gas Sensor for Simultaneous and Fast Optical Sensing of HONO and CH4 in Ambient Air Based on a Quantum Cascade Laser

A new dual-gas sensor has been developed using a quantum cascade laser (QCL) that operates at 1255 cm
⁻¹
for fast and simultaneous measurements of nitrous acid (HONO) and methane (CH
4
). The sensor uses direct absorption spectroscopy to detect HONO and CH
4
in the air, with a multi-pass absorption cell that has a path length of 173m. The sensor can detect HONO and CH
4
with minimum detection limits (1σ) of 198ppt and 2.95ppb, respectively, with an integration time of 1s. These detection limits can be improved to 39ppt and 0.31ppb, respectively, with an optimum integration time of 100s. The sensor can be used to monitor variations in the mixing ratios of HONO and CH
4
in the atmosphere, as well as basic meteorological parameters, to study the sources and sinks of HONO and monitor CH
4
pollution in the air.