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

Abstract

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.

Characterization of H2S QEPAS detection in methane-based gas leaks dispersed into environment

“…The use of QTFs avoids the need for a photodetector, which is mandatory for multipass cells and cavity-based spectroscopy [19] . Reduced dimensions, high sensitivity and fast response time make QEPAS a perfect candidate for realization of compact and portable sensors to be employed for on-site measurements [20] , [21] , [22] . Recently, PAS and QEPAS sensors were developed both for hydrocarbon detection at high concentration or at trace-level [23] , [24] , biomedical applications [25] and detection of dangerous and toxic gases [26] , [27] .…”

Ultra-sensitive ppb-level methane detection based on NIR all-optical photoacoustic spectroscopy by using differential fiber-optic microphones with gold-chromium composite nanomembrane

“…Beyond conventional methods such as electro-chemistry and gas chromatography [5] , [6] , optical methods allow improved selectivity and sensitivity as well as fast response. Optical methods using laser absorption spectroscopy (LAS) based on the ‘finger-print’ absorption lines of molecules, such as tunable diode laser absorption spectroscopy (TDLAS), cavity ring-down spectroscopy (CRDS) and photoacoustic spectroscopy (PAS) [7] , [8] , [9] , [10] , have been widely investigated for trace gas detection. TDLAS-based sensors have been widely commercialized [11] , and it fundamentally relies on the long optical path and superior photodetectors to achieve favorable sensing performance.…”

Parts-per-billion-level detection of hydrogen sulfide based on doubly resonant photoacoustic spectroscopy with line-locking

“…Photoacoustic spectroscopy serves as an alternative option with wide dynamic range, excitation wavelength independence, and no need for photodetectors, which has been demonstrated for the detection of numerous inorganic and organic trace gases [20] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] . Particularly, exploiting a tiny quartz tuning fork (QTF) [42] , [43] , [44] , [45] as the acoustic transducer provides practical attraction with high sensitivity, good immunity to environmental acoustic noise, tiny size, low cost, and ultra-low gas consumption [46] . The acoustic signal scales linearly with laser power, rather than a long absorption path.…”