In this work, we report on the implementation of a multi-quantum cascade laser (QCL) module as an innovative light source for quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing. The source is composed of three different QCLs coupled with a dichroitic beam combiner module that provides an overlapping collimated beam output for all three QCLs. The 3λ-QCL QEPAS sensor was tested for detection of NO₂, SO₂, and NH₃ in sequence in a laboratory environment. Sensitivities of 19.99 mV/ppm, 19.39 mV/ppm, and 73.99 mV/ppm were reached for NO₂, SO₂, and NH₃ gas detection, respectively, with ultimate detection limits of 9 ppb, 9.3 ppb, and 2.4 ppb for these three gases, respectively, at an integration time of 100 ms. The detection limits were well below the values of typical natural abundance of NO₂, SO₂, and NH₃ in air.

This study presents the performance of a multi-gas sensor for greenhouse detection based on quartz-enhanced photoacoustic spectroscopy (QEPAS). The QEPAS sensor exploits an innovative, compact three-wavelength laser module as excitation source. The module integrates three interband cascade laser chips with a beam combining system, all enclosed in a compact metallic package with sizes of 40 × 52 × 17 mm to generate a single output beam. The multi-gas QEPAS sensor was tested in a laboratory environment for the sequential detection of two greenhouse gases, methane (CH₄) and carbon dioxide (CO₂), and a precursor greenhouse gas, carbon monoxide (CO). At an integration time of 100 ms, minimum detection limits of 21 ppb, 363 ppb, and 156 ppb, were estimated for CH₄, CO_2, and CO detection, respectively, all well below their natural abundance in air.

This study presents a computational method to identify volatile organic compound (VOC) artifacts introduced by breath sampling hardware. To exclude endogenous biological variability, ambient air was collected using two sampling devices working in the same experimental conditions: the Mistral end-tidal breath sampler and the ACTI-VOC PLUS pump, a low-emission reference system. VOCs were pre-concentrated on sorbent-packed thermal desorption (TD) tubes and analyzed by TD–gas chromatography–mass spectrometry (TD–GC–MS). Differential chromatograms obtained by subtracting ACTI-VOC signals from Mistral traces were processed using stationary wavelet transform (SWT) to selectively enhance high-frequency features indicative of artifactual emissions. Four new compounds not previously associated with Mistral sampling hardware were consistently detected in Mistral samples and were absent in ACTI-VOC pump controls: 1,3,5-trioxane, 1,3,5,7-tetroxane, (Acetyloxy)acetic acid, and N,N-dimethylformamide. These molecules are indicative of polymer degradation, acetal resin breakdown, and material off-gassing specific to the breath sampler.