Compact and portable quartz-enhanced photoacoustic spectroscopy sensor for carbon monoxide environmental monitoring in urban areas

• Published in: Photoacoustics (Munich) 2022-03, Vol.25, p.100318-100318, Article 100318
• Main Authors: Sgobba, Fabrizio, Sampaolo, Angelo, Patimisco, Pietro, Giglio, Marilena, Menduni, Giansergio, Ranieri, Ada Cristina, Hoelzl, Christine, Rossmadl, Hubert, Brehm, Christian, Mackowiak, Verena, Assante, Dario, Ranieri, Ezio, Spagnolo, Vincenzo
• Format: Article
• Language: English
• Subjects: Carbon monoxide; Energy relaxation processes; Environmental monitoring; Gas sensing; Quartz enhanced photoacoustic spectroscopy
• ISSN: 2213-5979; 2213-5979
• DOI: 10.1016/j.pacs.2021.100318

We report on the realization, calibration, and test outdoor of a 19-inches rack 3-units sized Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) trace gas sensor designed for real-time carbon monoxide monitoring in ambient air. Since CO acts as a slow energy relaxer when excited in the mid-infrared spectral region, its QEPAS signal is affected by the presence of relaxation promoters, such as water vapor, or quenchers like molecular oxygen. We analyzed in detail all the CO relaxation processes with typical collisional partners in an ambient air matrix and used this information to evaluate oxygen and humidity-related effects, allowing the real CO concentration to be retrieved. The sensor was tested outdoor in a trafficked urban area for several hours providing results comparable with the daily averages reported by the local air inspection agency, with spikes in CO concentration correlated to the passages of heavy-duty vehicles.