EGU25-18041, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-18041
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Real time monitoring of N2O and CO emissions from vehicles using a quartz-enhanced photoacoustic sensor
Mariagrazia Olivieri1, Andrea Zifarelli2, Angelo Sampaolo1, Vincenzo Spagnolo1, and Pietro Patimisco2
Mariagrazia Olivieri et al.
  • 1Politecnico di Bari, Fisica, Italy
  • 2Università degli studi di Bari,Fisica, Italy

Greenhouse gases represent a crucial component of Earth's atmospheric system, playing a fundamental role in maintaining the planet's heat balance through their ability to absorb and emit infrared radiation. Anthropogenic activities have increased the atmospheric concentration of these gases, leading to enhanced global warming effects. The primary greenhouse gases include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and water vapor (H₂O). Among the other pollutants, carbon monoxide (CO) stands out as one of the most hazardous for human health. In urban areas, vehicle emissions represent the primary source of CO, produced through incomplete fuel combustion, with concentrations significantly higher than in unpolluted areas (∼50 ppb). Furthermore, vehicles emissions, particularly from those equipped with catalytic converters, partially contribute to the global atmospheric N2O budget, whose atmospheric concentration is ~300 ppb. The deployment of portable and reliable sensors to monitor these emissions is crucial for understanding their sources, assessing their impact, and developing effective mitigation strategies. 
Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) sensors offer an effective solution for monitoring air pollutants, providing high selectivity and sensitivity, compact dimensions, and rapid response times. Photoacoustic (PAS) basic principle consists in detecting sound waves induced by gas non-radiative energy relaxation as consequence of infrared modulated light absorption. QEPAS represents an evolution of the PAS approach and exploits a quartz tuning fork (QTF) to transduce the acoustic wave into an electric signal. Mid-IR Quantum Cascade Lasers (QCLs) have been employed as light source in QEPAS-based sensor to target the absorption bands of both N2O and CO.
Here we report on the realization of a QEPAS-based system employing a QCL with a central emission wavelength at 4.61 μm and a T-shaped QTF coupled with a pair of acoustic resonator tubes to amplify the sound wave. A ~1 min ramp was added to the fast laser modulation to scan the 2190.6-2188.7 cm-1 spectral range, where well-resolved absorption features of N2O and CO were selected. Laboratory calibrations with certified gas cylinders demonstrated the sensor's ability to detect N₂O and CO at hundreds and tens of ppb level, respectively, at a working pressure of 300 Torr and an integration time of 100 ms. We demonstrated the sensor capability to continuously monitor the QEPAS signal of the two gases both in indoor and outdoor environments. Indoor measurements were carried out over several days by sampling air inside the laboratory, while outdoor measurements took place in a university parking area in Bari to continuously monitor vehicle emissions. During spectral scans, the laser power, the sample temperature and its water vapor content was continuously measured, to eventually compensate for their influence on QEPAS signal. The resulting performances demonstrated its applicability for the realization of a compact and portable sensor for emission monitoring in urban areas.

How to cite: Olivieri, M., Zifarelli, A., Sampaolo, A., Spagnolo, V., and Patimisco, P.: Real time monitoring of N2O and CO emissions from vehicles using a quartz-enhanced photoacoustic sensor, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18041, https://doi.org/10.5194/egusphere-egu25-18041, 2025.