Acetylene-enhanced methane-QEPAS sensing
Jin Sun, Ying He, Shunda Qiao, Chu Zhang, Yufei Ma
Abstract
Methane (CH 4 ), as a critical greenhouse gas and explosive hazard, demands highly sensitive detection for environmental monitoring and industrial safety. To address the limitation of its slow relaxation in quartz-enhanced photoacoustic spectroscopy (QEPAS), this paper reported a novel acetylene (C 2 H 2 )-enhanced QEPAS technique for CH 4 sensing for the first time to our knowledge. Unlike the commonly used catalyst of water vapor (H 2 O), whose concentration in the air frequently changes and causes fluctuations in both the QEPAS signal level and the characteristics of the quartz tuning fork (QTF), C 2 H 2 accelerates CH 4 relaxation without inducing significant shifts in the QTF frequency. Firstly, the catalytic effect of C 2 H 2 molecules on the CH 4 relaxation process was analyzed. Systematic investigations revealed that increasing C 2 H 2 concentration enhances CH 4 -QEPAS signal intensity in three distinct phases: rapid growth, gradual saturation, and eventual stabilization. At 6000 ppm C 2 H 2 , the CH 4 -QEPAS signal amplitude increased by 2.53-fold compared to the situation without C 2 H 2 . The C 2 H 2 -enhanced CH 4 -QEPAS system maintained excellent linearity (R 2 = 0.9999) across 1000–12,000 ppm CH 4 . Allan deviation analysis confirmed a minimum detection limit (MDL) of 540 ppb at 1000 s average time, demonstrating excellent long-term stability. This work not only provides a robust strategy for CH 4 detection but also expands the application of QEPAS in gas relaxation dynamics modulation, highlighting C 2 H 2 as a superior relaxation promoter for other molecules with a slow relaxation rate.