The applicability of cantilever-enhanced photoacoustic spectroscopy (CEPAS), which exploits the unique properties of a micromechanical lever sensor (cantilever) in combination with tunable quantum cascade lasers (QCLs), is evaluated for the monitoring of several species produced by biomass burning. The detection limits of the selected molecules (HCOOH, CH3CN, CH3OH, CH3COCH3, CO2, and N2O) for a commercial CEPAS unit (GASERA) used together with QCLs were estimated under laboratory conditions. The normalized noise equivalent absorption (NNEA) coefficients for these molecules were determined experimentally, and the theoretical detection limits for the relevant biomass-burning products, accessed in the spectral ranges of available commercial QCLs in the mid-infrared region, were extrapolated using the determined NNEA values and the spectra simulated with the SpectraPlot software.

Photoacoustic spectroscopy is a detection method in which the light source energy is converted to sound [1], subsequently the sound captured by microphone. This method can be used for quantitative chemical analysis at ultra-low concentrations of gaseous species or samples with low absorption coefficient. Quartz enhanced photoacoustic spectroscopy replaces the classical conventional microphone and enables rapid and highly sensitive detection of trace gas concentrations, when using quartz tuning fork with a high quality factor [2]. Tunable quantum cascade laser partly covering acetonitrile infrared spectra [3] was employed in this study as an excitation source for quartz enhanced photoacoustic spectroscopy. Vapor of acetonitrile was used as measuring gas. From the practical point of view this gas is of importance as a marker of explosive compounds such as trinitrotoluene and hexogen [4], or it can be released into the atmosphere during combustion of biomass [5]. Case specific design of the photoacoustic cell and experimental setup for the purposes of quantum cascade laser -quartz enhanced photoacoustic spectroscopy detection is finally reported within this work.