Abstract
Increasing awareness of the adverse health effects of air pollution leads to a demand of low-cost sensors for the measurement of pollutants such as NO2. However, commercially available low-cost sensors lack accuracy and long-term stability, and suffer from cross-sensitivity to other gases. These drawbacks can be overcome by the method of quartz-enhanced photoacoustic spectroscopy (QEPAS). In QEPAS modulated light is absorbed by the NO2 molecules, which results in the production of a sound wave. The sound wave is detected by resonance of a quartz tuning fork, which results in a measurable electric signal. Due to the small size of the tuning forks, the gas sensing element can be smaller than 1 cm3. We present the first bare fork QEPAS setup for the ppb-level detection of NO2, which is ideally suited for environmental trace gas detection without the need of using micro-resonators. Micro-resonators are commonly used to amplify photoacoustic signals. However, micro-resonators have different dependencies on environmental conditions than tuning forks, which makes them difficult to operate in changing conditions. In contrast, our bare fork QEPAS setup is more robust and easily adopted by the use of a low-cost temperature and humidity sensor. By using acoustic filters the integration time could be increased to offer higher sensitivity at a continuous flow rate of 200 std cm3 min−1. The 1σ noise equivalent concentration is determined to 21 ppb NO2 in synthetic air for 120 s measurement time, allowing detection which satisfies international health and safety standards thresholds.
Highlights
Despite adverse health effects, premature deaths and high costs of air pollution, citizens even in the EU are still exposed to pollutant concentrations exceeding the EU and WHO reference concentrations [1]
Our approach for sensing NO2 is based on quartz-enhanced photoacoustic spectroscopy (QEPAS) [5] to overcome the aforementioned drawbacks
In contrast to ob-QEPAS, where production tolerances of micro-resonators would make calibration in a wide parameter space, spanned by temperature, humidity and NO2 concentration necessary, one linearity curve is sufficient in bf-QEPAS
Summary
Premature deaths and high costs of air pollution, citizens even in the EU are still exposed to pollutant concentrations exceeding the EU and WHO reference concentrations [1]. Among the pollutants of highest interest is nitrogen dioxide (NO2). Air pollution monitoring is carried out at low spatial resolution due to high costs of highly accurate measurement equipment [3]. To achieve higher spatial resolution, a denser sensor network of low-cost sensors is required. The detection of NO2 in sensor networks is usually done by electrochemical-based sensors. These sensors are lowcost but lack long-term stability and suffer from cross sensitivity to other gases [4]. Our approach for sensing NO2 is based on quartz-enhanced photoacoustic spectroscopy (QEPAS) [5] to overcome the aforementioned drawbacks
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
