2021
Fu, L., Yang, M., Niu, J., Ren, W.*, You, R.* 2021. Transient tracer gas measurements: development and evaluation of a fast-response SF6 measuring system based on quartz-enhanced photoacoustic spectroscopy. Indoor Air, 32 (1), e12952.
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Abstract: This study aims to develop a fast-response sulfur hexafluoride (SF6) measuring system, and evaluate its performance in tracer gas measurements for studying transient airborne contaminant transport. The new system is based on a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor using a quantum cascade laser. Transient SF6 tracer gas measurements were carried out in an environmental chamber with an instantaneous source using both the QEPAS system and a traditional commercial instrument. Real-time SF6 concentrations, peak SF6 concentrations and average SF6 concentrations for one room time constant under two air change rates obtained by the two instruments were compared. The results show that the QEPAS system, which features a 0.4 s data-acquisition interval, can provide detailed real-time SF6 concentrations even when the concentration is changing rapidly. The QEPAS system successfully captured the peak SF6 concentrations for all the studies cases, while commercial instrument failed in most studied cases. In most of the cases, the two instruments obtained similar average SF6 concentrations for one room time constant. However, when the concentration was in rapid change, the two systems would report significantly different results. The QEPAS system can be potentially applied in transient tracer gas measurements under complex scenarios.
2019
Wang, Z., Yang, M., Fu, L., Chen, C., You, R.*, Ren, W*. 2020. Rapid field measurement of ventilation rate using a quartz-enhanced photoacoustic SF6 gas sensor. Measurement Science and Technology, 31: 085105.
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Abstract: We reported the development of a quartz-enhanced photoacoustic sulfur hexafluoride (SF6) sensor for ventilation studies using a continuous-wave distributed-feedback quantum cascade laser (QCL) at 10.5 µm. The SF6 sensor was developed by detecting the gas-absorption induced acoustic wave using a tiny quartz tuning fork that is enclosed in a gas cell with a sample volume of 2.5 mL. By locking the QCL wavelength at the absorption peak of SF6, we obtained a recording time interval of 0.4 s and a detection limit of 4.6 ppb. The sensor response time (t90) was found to be 2.8 s at a flow rate of 550 mL/min. The sensor was then implemented in measuring air exchange rates (AERs) in a laboratory room using the standard tracer gas concentration decay method. Our measurements are in good agreement with a commercial analyzer when studying two typical passive ventilation scenarios of infiltration and natural ventilation. Additionally, the developed photoacoustic gas sensor is fast enough to capture the transient variations of the SF6 concentration during natural ventilation. This study provides a promising method of studying transient contaminant transport that remains a major challenge in air quality research.
