Fourier-Transform Infrared Differential Photoacoustic Spectroscopy (FTIR-DPAS) for Simultaneous Monitoring of Multiple Air Contaminants/Trace Gases

Abstract

Air pollutants have severe impact on the global environment and the health of human beings. There is an urgent need for cost-effective devices for trace gas monitoring in ambient conditions. However, water vapor in ambient air is still an obstacle in the trace gas absorption detection field due to its complex and strong infrared absorbing characteristics. In this work, a step-scan Fourier-transform infrared differential photoacoustic spectroscopy (FTIR-DPAS) methodology developed in our laboratory through the introduction of two identical T-resonators for enhancing and resolving the DPA signal from two potentially pollutant gases is extended to multiple ambient gas components: carbon dioxide (CO₂) and acetylene (C₂H₂). A key feature of this technique is the ability to resolve hidden target spectral components in ambient air: Despite the fact that the acetylene absorption peaks lie within the strong water vapor absorption band, the infrared PA absorption spectra of acetylene and carbon dioxide are detected with high sensitivity and selectivity in the presence of significant interference of water vapor in the laboratory ambient air, thereby confirming the superiority and capability of step-scan FTIR-DPAS configuration to effectively and totally suppress often dominant background water signals and simultaneously detect multiple trace gases.