Toward an Event-Based and Quality-Assured Air Sampling: A Portable System for Sensing and Sampling Volatile Organic Compounds

Abstract

Sensors for monitoring volatile organic compounds are commonly employed for air quality control in indoor and outdoor environment. They provide data with high temporal and spatial resolution. Although these sensors can detect possible concentration changes very quickly, they do not provide any information about the composition of air pollutants. Furthermore, the measurements are strongly influenced by gaseous interfering compounds and meteorological conditions. It is necessary to carry out measurements in the laboratory for reliable and credible data. The adsorptive enrichment of air samples on solid adsorbents is the most commonly used method for taking air samples. We wanted to combine the advantages of both approaches. Therefore, a portable modular sensor and multitube sequential sampling system has been developed. It combines real-time online monitoring of ambient air using a gas sensor array and quality-assured active sampling. The sensor module consists of an optimized 3D-printed sensor chamber where up to 4 gas sensors can be integrated. The sampler module was equipped with up to 32 commercially available sorbent tubes. The inlet pressure of the mass flow controller and temperature are permanently recorded, allowing the detection of a leakage or tube clogging during the sampling procedure. The remote access to the data from both the sensors and the sampler parameters allows the identification of possible malfunctions, which limits the necessary presence of an operator during long-term measurements. The power supply is realized with a lightweight battery, which can be charged by solar panels.

1

Streamlines through the sensor chamber with and without swirl plates.

2

Process diagram of the sampling module.

3

Enrichment unit in the sampling module.

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Calibrations of the O₃ sensor in dependence on (A) temperature and (B) relative humidity (rH).

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Calibrations of α-pinene using the PID sensor in dependence on relative humidity (rH).

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Settings for the start options of the sampler module using the web interface.

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Signal intensities in GC–MS depending on the concentration of ambient air.

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Long-term stability of loaded sorbent tubes in the sampler module.

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Comparison of chromatograms of two air samples taken in an urban area.